what are the components of a viral envelope
viral glycoproteins phospholipids proteins
7404513
Viral envelope Some viruses (e.g. HIV and many animal viruses) have viral envelopes covering their protective protein capsids. The envelopes are typically derived from portions of the host cell membranes (phospholipids and proteins), but include some viral glycoproteins. They may help viruses avoid the host immune system. Glycoproteins on the surface of the envelope serve to identify and bind to receptor sites on the host's membrane. The viral envelope then fuses with the host's membrane, allowing the capsid and viral genome to enter and infect the host. The cell from which the virus itself buds will often die or be
Viral envelope
17613232
and contain viral envelope, matrix, and nucleocapsid components. The overall cylinders are generally approximately 80 nm in diameter, and have a virally encoded glycoprotein (GP) projecting as 7-10 nm long spikes from its lipid bilayer surface. The cylinders are of variable length, typically 800 nm, but sometimes up to 1000 nm long. The outer viral envelope of the virion is derived by budding from domains of host cell membrane into which the GP spikes have been inserted during their biosynthesis. Individual GP molecules appear with spacings of about 10 nm. Viral proteins VP40 and VP24 are located between the envelope
Ebola virus
4505669
structural proteins are components for the capsid and the envelope of the virus. The genetic material of a virus is stored within a viral protein structure called the capsid. The capsid is a "shield" that protects the viral nucleic acids from getting degraded by host enzymes or other types of pesticides or pestilences. It also functions to attach the virion to its host, and enable the virion to penetrate the host cell membrane. Many copies of a single viral protein or a number of different viral proteins make up the capsid, and each of these viral proteins are coded for
Viral protein
7404513
Viral envelope Some viruses (e.g. HIV and many animal viruses) have viral envelopes covering their protective protein capsids. The envelopes are typically derived from portions of the host cell membranes (phospholipids and proteins), but include some viral glycoproteins. They may help viruses avoid the host immune system. Glycoproteins on the surface of the envelope serve to identify and bind to receptor sites on the host's membrane. The viral envelope then fuses with the host's membrane, allowing the capsid and viral genome to enter and infect the host. The cell from which the virus itself buds will often die or be
Viral envelope
15684288
retroviruses. Retroviral matrix protein Retroviral matrix proteins are components of envelope-associated capsids of retroviruses. These proteins line the inner surface of viral envelopes and are associated with viral membranes. Matrix proteins are produced as N-terminal domains of Gag precursor polyproteins. The Gag polyprotein directs the assembly and release of virus particles from infected cells. The Gag polyprotein has three domains required for activity: an N-terminal membrane-binding (M) domain (which corresponds to the matrix protein) that directs Gag to the plasma membrane, an interaction (I) domain involved in Gag aggregation, and a late assembly (L) domain that mediates the budding process
Retroviral matrix protein
15684285
Retroviral matrix protein Retroviral matrix proteins are components of envelope-associated capsids of retroviruses. These proteins line the inner surface of viral envelopes and are associated with viral membranes. Matrix proteins are produced as N-terminal domains of Gag precursor polyproteins. The Gag polyprotein directs the assembly and release of virus particles from infected cells. The Gag polyprotein has three domains required for activity: an N-terminal membrane-binding (M) domain (which corresponds to the matrix protein) that directs Gag to the plasma membrane, an interaction (I) domain involved in Gag aggregation, and a late assembly (L) domain that mediates the budding process .
Retroviral matrix protein
4812396
Virus-like particle Virus-like particles resemble viruses, but are non-infectious because they contain no viral genetic material. The expression of viral structural proteins, such as envelope or capsid proteins, can result in the self-assembly of virus like particles (VLPs). VLPs derived from the Hepatitis B virus and composed of the small HBV derived surface antigen (HBsAg) were described in 1968 from patient sera. VLPs have been produced from components of a wide variety of virus families including Parvoviridae (e.g. adeno-associated virus), Retroviridae (e.g. HIV), Flaviviridae (e.g. Hepatitis C virus) and bacteriophages (e.g. Qβ, AP205). VLPs can be produced in multiple cell
Virus-like particle
13587719
(VSV), short VSV-G. These envelope proteins transduce to all cell types. Pseudotyping Pseudotyping is the process of producing viruses or viral vectors in combination with foreign viral envelope proteins. The result is a pseudotyped virus particle. With this method, the foreign viral envelope proteins can be used to alter host tropism or an increased/decreased stability of the virus particles. Pseudotyped particles do not carry the genetic material to produce additional viral envelope proteins, so the phenotypic changes cannot be passed on to progeny viral particles. For example, pseudotyping allows one to specify the character of the envelope proteins. A frequently
Pseudotyping
7262439
in a protein layer called the tegument containing both viral proteins and viral mRNAs and a lipid bilayer membrane called the envelope. This whole particle is known as a virion. All herpesviruses are nuclear-replicating—the viral DNA is transcribed to mRNA within the infected cell's nucleus. Infection is initiated when a viral particle contacts a cell with specific types of receptor molecules on the cell surface. Following binding of viral envelope glycoproteins to cell membrane receptors, the virion is internalized and dismantled, allowing viral DNA to migrate to the cell nucleus. Within the nucleus, replication of viral DNA and transcription of
Herpesviridae
4505671
membrane called the viral envelope. In most cases, the viral envelope is obtained by the capsid from the host cell's plasma membrane when a virus leaves its host cell through a process called budding. The viral envelope is made up of a lipid bilayer embedded with viral proteins, including viral glycoproteins. These viral glycoproteins bind to specific receptors and coreceptors on the membrane of host cells, and they allow viruses to attach onto their target host cells. Some of these glycoproteins include: Viral glycoproteins play a critical role in virus-to-cell fusion. Virus-to-cell fusion is initiated when viral glycoproteins bind to
Viral protein
13587718
Pseudotyping Pseudotyping is the process of producing viruses or viral vectors in combination with foreign viral envelope proteins. The result is a pseudotyped virus particle. With this method, the foreign viral envelope proteins can be used to alter host tropism or an increased/decreased stability of the virus particles. Pseudotyped particles do not carry the genetic material to produce additional viral envelope proteins, so the phenotypic changes cannot be passed on to progeny viral particles. For example, pseudotyping allows one to specify the character of the envelope proteins. A frequently used protein is the glycoprotein G of the Vesicular stomatitis virus
Pseudotyping
4505672
cellular receptors. The fusion of the viral envelope with the cellular membrane requires high energy to occur. Viral membrane fusion proteins act as catalysts to overcome this high energy barrier. Following viral glycoprotein binding to cellular receptors, viral membrane fusion proteins undergo a change in structure conformation. This change in conformation then facilitates the destabilization and fusion of the viral envelope with the cellular membrane by allowing fusion loops (FLs) or hydrophobic fusion peptides (FPs) on the viral envelope to interact with the cell membrane. Most viral membrane fusion proteins would end up in a hairpin-like conformation after fusion, in
Viral protein
9156360
a layered structure: Virions consist of an envelope, a tegument, a nucleocapsid, and a core. Tegument is disordered; they do not display a structure and proteins in variable amounts are arranged sometimes in an asymmetric layer located between envelope and capsid. The viral capsid is contained within a spherical envelope which is 120–200 nm in diameter. Surface projections on envelope (viral receptors) are densely dispersed and contain small spikes that evenly dot the surface. The capsid/nucleocapsid is round with triangulation number T=16 and exhibits icosahedral symmetry. The capsid is isometric and has a diameter of 100–110 nm. The capsid consists
Varicellovirus
3668134
There is evidence for a p53-dependent mechanism. Group: ssRNA(+) The spherical virus particles (virions) of Togaviridae have a diameter of 50 to 70 nm and are covered by a lipid membrane (viral envelope), derived from the host cell membrane. There are prominent "spikes" (projections) of 6 nm composed of the viral envelope proteins E1 and E2 embedded in the membrane. Inside the lipid envelope is a capsid of 40 nm in diameter. The E1 glycoprotein is considered immunodominant in the humoral response induced against the structural proteins and contains both neutralizing and hemagglutinating determinants. The genome has 9,762 nucleotides and
Rubella virus
14961999
Herpesvirus glycoprotein B Herpesvirus glycoprotein B is a viral glycoprotein that is involved in the viral cell entry of Herpes simplex virus (HSV). Herpesviruses have an envelope and an outer lipid bilayer which contains twelve surface glycoproteins. For infectivity to be attained, the double stranded DNA genome of HSV must enter the host cell through means of fusion of its envelope with the cellular membrane or via endocytosis. Other viral glycoproteins involved in the process of viral cell entry include gC, gB, gD, gH, and gL, but only gC, gB, gD, and gH are required for the fusion of the
Herpesvirus glycoprotein B
1307586
in the control of other viral diseases - priming the adaptive immunity to recognize the viral envelope proteins - have failed to work against HIV. Many factors make the development of an HIV vaccine different to other classic vaccines: The epitopes of the viral envelope are more variable than those of many other viruses. Furthermore, the functionally important epitopes of the gp120 protein are masked by glycosylation, trimerisation and receptor-induced conformational changes making it difficult to block with neutralizing antibodies. The ineffectiveness of previously developed vaccines primarily stems from two related factors: The difficulties in stimulating a reliable antibody response
HIV vaccine
12530305
known that virions converge to the microtubule organizing center, interact with acidic endosomes and finally enter the target endosomes for genome release. Once inside the cell, the acidic conditions in the endosome cause two events to happen: First, part of the hemagglutinin protein fuses the viral envelope with the vacuole's membrane, then the M2 ion channel allows protons to move through the viral envelope and acidify the core of the virus, which causes the core to disassemble and release the viral RNA and core proteins. The viral RNA (vRNA) molecules, accessory proteins and RNA-dependent RNA polymerase are then released into
Influenza
8341894
to viruses that do not contain an envelope. Well studied examples are the viruses that infect bacteria, known as bacteriophages (or simply phages). Typical phages have long tails used to attach to receptors on the bacterial surface. Prior to entry, a virus must attach to a host cell. Attachment is achieved when specific proteins on the viral capsid or viral envelope bind to specific proteins called receptor proteins on the cell membrane of the target cell. A virus must now enter the cell, which is covered by a phospholipid bilayer, a cell's natural barrier to the outside world. The process
Viral entry
15914788
230 nm and width of about 75 nm at the broad end. The narrow end projects beyond the viral envelope and is likely used to inject the viral DNA into host cells. The broad end possesses about 20 thin filaments, each that are regularly distributed in a ring. Inside the envelope is a funnel-shaped protein coat that houses the viral DNA. The genome of ampullaviruses is linear, double-stranded DNA that is about 23.8 kilobases in length. The genome contains an estimated 56 or 57 open reading frames that encode for at least six structural proteins. Ampullaviridae Ampullaviridae is a family
Ampullaviridae
6078770
encephalitis virus have all been used to develop viral vectors for gene delivery. Of particular interest are the chimeric viruses that may be formed with alphaviral envelopes and retroviral capsids. Such chimeras are termed pseudotyped viruses. Alphaviral envelope pseudotypes of retroviruses or lentiviruses are able to integrate the genes that they carry into the expansive range of potential host cells that are recognized and infected by the alphaviral envelope proteins E2 and E1. The stable integration of viral genes is mediated by the retroviral interiors of these vectors. There are limitations to the use of alphaviruses in the field of
Alphavirus
13136968
of an outer lipid envelope and an icosahedral nucleocapsid core composed of protein. The nucleocapsid encloses the viral DNA and a DNA polymerase that has reverse transcriptase activity similar to retroviruses. The outer envelope contains embedded proteins which are involved in viral binding of, and entry into, susceptible cells. The virus is one of the smallest enveloped animal viruses with a virion diameter of 42 nm, but pleomorphic forms exist, including filamentous and spherical bodies lacking a core. These particles are not infectious and are composed of the lipid and protein that forms part of the surface of the virion,
Hepatitis B virus
16177382
gene therapy vector. To this end, many vectors have been developed in which the endogenous viral envelope proteins have been replaced by either envelope proteins from other viruses, or by chimeric proteins. Such chimera would consist of those parts of the viral protein necessary for incorporation into the virion as well as sequences meant to interact with specific host cell proteins. Viruses in which the envelope proteins have been replaced as described are referred to as pseudotyped viruses. For example, the most popular retroviral vector for use in gene therapy trials has been the lentivirus Simian immunodeficiency virus coated with
Vectors in gene therapy
188428
development of the virion such as reverse transcriptase, proteases, ribonuclease and integrase. A matrix composed of the viral protein p17 surrounds the capsid ensuring the integrity of the virion particle. This is, in turn, surrounded by the viral envelope, that is composed of the lipid bilayer taken from the membrane of a human host cell when the newly formed virus particle buds from the cell. The viral envelope contains proteins from the host cell and relatively few copies of the HIV Envelope protein, which consists of a cap made of three molecules known as glycoprotein (gp) 120, and a stem
HIV
7766398
ordered as UL-IRS-US-TRS. There are 78 predicted proteins encoded by the genome. DVE has similar morphology to other "Herpesvirales" viruses. Common elements of herpviruses include a “DNA core, icosahedral capsid, tegument, and envelope”. The nucleocapsid of HPV-1 is 75 micrometers wide and the envelope diameter is 181 micrometers. Three phases (immediate early (IE), early (E), and late (L)) of infection dictate the transcription of certain DEV genes. Immediate early begins after infection and before viral DNA replication. During this phase IE genes are transcribed without other proteins. The E genes are also transcribed before viral DNA replication, but are dependent
Duck plague
2415021
infects CD4+ T cells. The viral RNA is packed into the icosahedral capsid which is contained inside the protein inner envelope. The lipid outer envelope is of host cell origin but contains viral transmembrane and surface proteins. The virion is spherical in shape with a diameter of about 100 nm. Seven HTLV-1 genotypes are recognised—HTLV-1a through HTLV-1g. It is estimated that from 10 to 20 million people worldwide are infected; 3–8 million of them are in Africa. The most widespread genotype is type A. Types B, D, E, F and G have only been isolated from Central Africa. Type C
Human T-lymphotropic virus 1
7601741
in the cytoplasm. The late proteins form the capsid and the receptors on the surface of the virus. Packaging of the viral particles — including the genome, core and the capsid - occurs in the nucleus of the cell. Here, concatemers of the viral genome are separated by cleavage and are placed into formed capsids. HSV-1 undergoes a process of primary and secondary envelopment. The primary envelope is acquired by budding into the inner nuclear membrane of the cell. This then fuses with the outer nuclear membrane, releasing a naked capsid into the cytoplasm. The virus acquires its final envelope
Herpes simplex virus
4223545
uncharacterized. ORF2 – dihydrofolate reductase ORF8 – gB – envelope glycoprotein involved in viral entry ORF9 – Pol8 – DNA polymerase required for viral DNA replication ORF10 – regulates RNA export and responses to type I IFNs ORF16 – vBcl2 ORF18, ORF24, ORF30, ORF31, ORF34, ORF66 – viral transcription factors required for the expression of late genes ORF21 – vTK – thymidine kinase ORF22 – gH – envelope glycoprotein involved in viral entry ORF23 – uncharacterized ORF25, ORF26 and ORF65 – capsid proteins ORF33 – involved in viral particle formation ORF34 – unclear function ORF35 – unclear function, mutant does
Kaposi's sarcoma-associated herpesvirus
20416416
packing of the genome in the nucleocapsid. The structure of the envelope is characterized by the spike-like projections of two viral proteins, the fusion protein (F) and hemagglutinin-neuraminidase (Hn) protein. However, these protein projections may differ between the nine serotypes of avian paramyxoviruses. The matrix protein (M) is believed to form the inner layer of the envelope and interacts with the F and Hn proteins on the outside of the viral envelope during viral entry. Avian paramyxovirus 2 has a negative-sense RNA genome that upon entry into the cell, must be transcribed into a positive-sense mRNA in order to produce
Avian paramyxovirus 2
11172472
Viral tegument A viral tegument or tegument, more commonly known as a viral matrix, is a cluster of proteins that lines the space between the envelope and nucleocapsid of all herpesviruses. The tegument generally contains proteins that aid in viral DNA replication and evasion of the immune response, typically with inhibition of signalling in the immune system and activation of interferons. The tegument is usually released shortly after infection into the cytoplasm. These proteins are usually formed within the late phase of the viral infectious cycle, after viral genes have been replicated. Much information regarding viral teguments has been gathered
Viral tegument
11172474
released into the cytoplasm upon entrance into the cell upon which many tegumental proteins become active. The tegument may also aid in insertion of the viral genome into host cell cytoplasm or nucleus. Teguments are generally in enveloped viruses which have nucleocapsids, as tegument proteins cannot be stored in an efficient fashion in capsid-only viruses. The best studied examples are the Herpesvirus family, in which the tegument is most prominent. Viral tegument A viral tegument or tegument, more commonly known as a viral matrix, is a cluster of proteins that lines the space between the envelope and nucleocapsid of all
Viral tegument
5937012
length. Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment of the viral proteins to host glycosaminoglycans (GAGs), which mediate cellular endocytosis of the virus. Fusion of the viral envelope with the plasma membrane releases the viral core into the host cytoplasm. Expression of early-phase genes by viral RNA polymerase begins at 30 minutes after infection. The viral core is completely uncoated as early expression ends, releasing the viral genome into the cytoplasm. At this point, intermediate genes are expressed, triggering genomic DNA replication by the viral DNA polymerase about 100 minutes post-infection. Replication follows the
Orthopoxvirus
15928114
cancer. Integration to the retroviral genome is critical for gene expression and viral replication. The viral genome is reversely transcribed into the DNA of the infected cell by viral reverse transcriptase, the DNA is then integrated into the host-cell chromosomes with the aid of the viral integrase. RNA transcripts are produced from integrated viral DNA and serve both as mRNAs to direct the synthesis of viral proteins and later as RNA genomes of the new viral particles.Viral particles escape from the cell by budding from the plasma membrane, each enclosed in a membrane envelope. The HIV-1 integrase (IN) is a
Discovery and development of integrase inhibitors
7766400
host cell causes separation of the nucleocapsid from viral DNA and proteins. Multiple necessary viral proteins are located within the envelope. DNA and proteins enter the host cell nucleus and turn-off host cell synthesis of nucleic acids, proteins, and other macro molecules. There are two hypothesized origins of replication in the IRS and TRS regions of the genome. Immature capsids are formed from coiled DNA. L genes are transcribed “after the synthesis of DNA and viral protein onset”. Virion DNA maturation occurs as the nucleocapids “budd through nuclear membrane”. Completed viral replication occurs within 12 hours of infection. Vacuoles of
Duck plague
6177571
protease. A matrix composed of an association of the viral protein p17 surrounds the capsid, ensuring the integrity of the virion particle. This is in turn surrounded by an envelope of host-cell origin. The envelope is formed when the capsid buds from the host cell, taking some of the host-cell membrane with it. The envelope includes the glycoproteins gp120 and gp41, which are responsible for binding to and entering the host cell. As the only proteins on the surface of the virus, the envelope glycoproteins (gp120 and gp41) are the major targets for HIV vaccine efforts. Over half of the
Structure and genome of HIV
7493603
components such as replicase enzymes, virus genetic material, and host proteins required for replication concentrate, and thereby increase the efficiency of replication. At the same time, large amounts of ribosomes, protein-synthesis components, protein folding chaperones, and mitochondria are recruited. Some of the membrane components are used for viral replication while some others will be modified to produce viral envelopes, when the viruses are enveloped. The viral replication, protein synthesis and assembly require a considerable amount of energy, provided by large clusters of mitochondria at the periphery of viroplasms. The virus factory is often enclosed by a membrane derived from the
Viroplasm
2541328
reticulum during prometaphase and the targeting of inner nuclear membrane protein-containing ER vesicles to the chromatin occurs during telophase in a reversal of this process. Membrane-forming vesicles aggregate directly to the surface of chromatin, where they fuse laterally into a continuous membrane. Ran-GTP is required for early nuclear envelope assembly at the surface of the chromosomes: it releases envelope components sequestered by importin β during early mitosis. Ran-GTP localizes near chromosomes throughout mitosis, but does not trigger the dissociation of nuclear envelope proteins from importin β until M-Cdk targets are dephosphorylated in telophase. These envelope components include several nuclear pore
Telophase
12530301
these varied shapes, the viral particles of all influenza viruses are similar in composition. These are made of a viral envelope containing two main types of glycoproteins, wrapped around a central core. The central core contains the viral RNA genome and other viral proteins that package and protect this RNA. RNA tends to be single stranded but in special cases it is double. Unusually for a virus, its genome is not a single piece of nucleic acid; instead, it contains seven or eight pieces of segmented negative-sense RNA, each piece of RNA containing either one or two genes, which code
Influenza
17613112
with a virion attaching to specific cell-surface receptors such as C-type lectins, DC-SIGN, or integrins, which is followed by fusion of the viral envelope with cellular membranes. The virions taken up by the cell then travel to acidic endosomes and lysosomes where the viral envelope glycoprotein GP is cleaved. This processing appears to allow the virus to bind to cellular proteins enabling it to fuse with internal cellular membranes and release the viral nucleocapsid. The "Ebolavirus" structural glycoprotein (known as GP1,2) is responsible for the virus' ability to bind to and infect targeted cells. The viral RNA polymerase, encoded by
Ebola virus disease
19707159
SARS-CoV E protein, which forms a pore that integrates membrane lipids whose polar head groups influence ion selectivity. Loss of membrane polarization can promote viral yields through a variety of mechanisms that operate throughout the viral life cycle. In enveloped viruses, viroporins are not highly concentrated in the viral envelope, but nevertheless their presence may promote viral entry into the cell; the influenza A virus provides a well-studied example. Viroporins in the membranes of organelles such as the Golgi apparatus can influence those organelles' internal environments, which can modulate protein trafficking of viral proteins or protect the proteins from the
Viroporin
6196215
Viral matrix protein Structural proteins linking the viral envelope with the virus core. They play a crucial role in virus assembly, and interact with the RNP complex as well as with the viral membrane. They are found in many enveloped viruses including paramyxoviruses, orthomyxoviruses, herpesviruses, retroviruses, filoviruses and other groups. An example is the M1 protein of the influenza virus, showing affinity to the glycoproteins inserted in the host cell membrane on one side and affinity for the RNP complex molecules on the other side, which allows formation at the membrane of a complex made of the viral ribonucleoprotein at
Viral matrix protein
2556922
a host’s antibodies can bind and trigger an immune response. Influenza type A viruses are categorized into subtypes based on the type of these two proteins on the surface of the viral envelope. There are 16 subtypes of HA and 9 subtypes of NA known, but only H 1, 2 and 3, and N 1 and 2 are commonly found in humans. The central core of a virion contains the viral genome and other viral proteins that package and protect the genetic material. Unlike the genomes of most organisms (including humans, animals, plants, and bacteria) which are made up of
Influenza A virus
2915080
During infection, viral fusion proteins used by the virus to enter the cell are transported to the cell surface, where they can cause the host cell membrane to fuse with neighboring cells. Typically, the viral families that can cause syncytium are enveloped because viral envelope proteins on the surface of the host cell are needed to fuse with other cells. But, certain members of the Reoviridae family are notable exceptions due to a unique set of proteins known as fusion-associated small transmembrane (FAST) proteins. Reovirus induced syncytium formation is not found in humans, but is found in a number of
Syncytium
7842295
Virosome A virosome is a drug or vaccine delivery mechanism consisting of unilamellar phospholipid membrane (either a mono- or bi-layer) vesicle incorporating virus derived proteins to allow the virosomes to fuse with target cells. As a drug or vaccine delivery mechanism they are biologically compatible with many host organisms and are also biodegradable. The use of reconstituted virally derived proteins in the formation of the virosome allows for the utilization of what would otherwise be the immunogenic properties of a live-attenuated virus, but is instead a safely killed virus. In contrast to liposomes, virosomes contain functional viral envelope glycoproteins: influenza
Virosome
14962002
but they are required for viral entry into the cell and constitute the core fusion machinery. The claim that gB is involved in fusion comes from the notable syncytial phenotype caused by certain mutations within the cytoplasmic domain of glycoprotein B, as well as its structural homology to other viral fusion proteins. Herpesvirus glycoprotein B Herpesvirus glycoprotein B is a viral glycoprotein that is involved in the viral cell entry of Herpes simplex virus (HSV). Herpesviruses have an envelope and an outer lipid bilayer which contains twelve surface glycoproteins. For infectivity to be attained, the double stranded DNA genome of
Herpesvirus glycoprotein B
2556921
made up of a viral envelope containing two main types of proteins, wrapped around a central core. The two large proteins found on the outside of viral particles are hemagglutinin (HA) and neuraminidase (NA). HA is a protein that mediates binding of the virion to target cells and entry of the viral genome into the target cell. NA is involved in release from the abundant non-productive attachment sites present in mucus as well as the release of progeny virions from infected cells. These proteins are usually the targets for antiviral drugs. Furthermore, they are also the antigen proteins to which
Influenza A virus
6178347
has proven extremely difficult due to its high degree of variability and shielding. Fostemsavir (BMS-663068) is a methyl phosphate prodrug of the small molecule inhibitor BMS-626529, which prevents viral entry by binding to the viral envelope gp120 and interfering with virus attachment to the host CD4 receptor. The HIV viral protein gp120 induces apoptosis of neuronal cells by inhibiting levels of furin and tissue plasminogen activator, enzymes responsible for converting pBDNF to mBDNF. gp120 induces mitochondrial-death proteins like caspases which may influence the upregulation of the death receptor Fas leading to apoptosis of neuronal cells, gp120 induces oxidative stress in
Envelope glycoprotein GP120
13891844
In primate lentiviruses there is usually an ORF for nef (negative factor); this is not present in BIV. BIV has a structure like all retroviruses, and contains two copies of its positive sense single stranded RNA genome. It has two compartments: the envelope and the core. The envelope comes from the host cell plasma membrane, the virus takes the membrane as it buds and then inserts viral glycoproteins into its envelope. The core of the virus contains Gag and Gag-Pol polyproteins. These polyproteins are cleaved in the mature virus to their functional forms. As mentioned before, leukocytosis and lymphadenopathy are
Bovine immunodeficiency virus
12418738
the association of viral capsid proteins with viral nucleic acid is called a nucleocapsid. The capsid and entire virus structure can be mechanically (physically) probed through atomic force microscopy. In general, there are four main morphological virus types: The poxviruses are large, complex viruses that have an unusual morphology. The viral genome is associated with proteins within a central disc structure known as a nucleoid. The nucleoid is surrounded by a membrane and two lateral bodies of unknown function. The virus has an outer envelope with a thick layer of protein studded over its surface. The whole virion is slightly
Virus
2473434
all sequences at the 5' end is 37-51 nt. The 3' noncoding regions differ: L segment 38-43 nt; M segment 168-229 nt; and S segment 370-730 nt. The 3' end of the S segment is conserved between the genera suggesting a functional role. Hantavirus virions are about 120-160 nanometers (nm) in diameter. The lipid bilayer of the viral envelope is about five nm thick and is embedded with viral surface proteins to which sugar residues are attached. These glycoproteins, known as Gn and Gc, are encoded by the M segment of the viral genome. They tend to associate (heterodimerize) with
Orthohantavirus
17276882
vector, one has to consider the biology of the infection process. The lentivirus is a retrovirus, meaning it has a single stranded RNA genome with a reverse transcriptase enzyme. Lentiviruses also have a viral envelope with protruding glycoproteins that aid in attachment to the host cell's outer membrane. The virus contains a reverse transcriptase molecule found to perform transcription of the viral genetic material upon entering the cell. Within the viral genome are RNA sequences that code for specific proteins that facilitate the incorporation of the viral sequences into the host cell genome. The "gag" domain codes for the structural
Lentiviral vector in gene therapy
6177574
presented on the native virus. Recombinant trimeric viral spikes are promising vaccine candidates as they display less non-neutralising epitopes than recombinant monomeric gp120 which act to suppress the immune response to target epitopes. HIV has several major genes coding for structural proteins that are found in all retroviruses as well as several nonstructural ("accessory") genes unique to HIV. The HIV genome contains nine genes that encode fifteen viral proteins. These are synthesized as polyproteins which produce proteins for virion interior, called Gag, group specific antigen; the viral enzymes (Pol, polymerase) or the glycoproteins of the virion "env" (envelope). In addition
Structure and genome of HIV
5367643
systemic infection. This protein forms structures called peplomers on one end of the budded virus particle but is not found on ODV (although several other proteins are only associated with the ODV form). Some differences also exist in the lipid composition of the viral envelope of the two forms. While the BV envelope consists of phosphatidylserine, ODV contains phosphatidylcholine and phosphatidylethanolamine. A nucleocapsid assembly-essential element (NAE) was identified in the AcMNPV genome. The NAE is an internal "cis"-element within the "ac83" gene. The nucleocapsid assembly is not dependent on the Ac83 protein product. During periods of evolution, the baculoviral envelope
Baculoviridae
1694204
cycle because it regulates the balance between viral replication and virion assembly. The HDV envelope protein has three of the HBV surface proteins anchored to it. The S region of the genome is most commonly expressed and its main function is to assemble subviral particles. HDV antigen proteins can combine with the viral genome to form a ribonucleoprotein (RNP) which when enveloped with the subviral particles can form viral-like particles that are almost identical to mature HDV, but they are not infectious. Researchers had concluded that the determinant of infectivity of HDV was within the N-terminal pre-S1 domain of the
Hepatitis D
19207698
it’s going to infect. In flavivirus virions, the fusion peptide is buried in dimmers of the fusion glycoprotein E. At low pH, the dimmers are disrupted, the proteins rotate to form trimers, and the fusion peptide is directed toward the cell membrane The viral envelope protein E attaches to host receptors, which mediates receptor-mediated endocytosis.. The viral nucleocapsid, as RNP, is released into the cytoplasm, where the RNA synthesis begins. The mechanism by which the contacts between the viral nucleocapsid and M protein, which forms a shell beneath the lipid bilayer, are broken to facilitate release of the nucleocapsid is
Entebbe bat virus
9269386
buffers used in this process. Inactivation of viruses by means of pasteurization can be very effective if the proteins that you are trying to protect are more thermally resistant than the viral impurities with which they are in solution. Some of the more prominent advantages of these types of processes are that they require simple equipment and they are effective for both enveloped "and" non-enveloped viruses. Because pasteurization involves increasing the temperature of solution to a value that will sufficiently denature the virus, it does not matter whether the virus has an envelope or not because the envelope alone cannot
Virus processing
6196216
the inner side indirectly connected to the viral glycoproteins protruding from the membrane. This assembly complex will now bud out of the cell as new mature viruses. Viral matrix proteins, like many other viral proteins, can exert different functions during the course of the infection. For example, in Rhabdoviruses, binding of M proteins to nucleocapsids is accountable for the formation of its “bullet” shaped virions. In herpesviruses, the viral matrix is usually called viral tegument and contains many proteins involved in viral entry, early gene expression and immune evasion. Viral matrix protein Structural proteins linking the viral envelope with the
Viral matrix protein
9805379
each encoding two different genes in an ambisense orientation. The two segments are termed 'short (S)' and 'long (L)' owing to their respective lengths. The short segment (around 3400 nucleotides in length) encodes the nucleocapsid protein and the glycoprotein precursor (GPC). The GPC is subsequently cleaved to form two viral glycoproteins, GP1 and GP2, which ultimately form the T-shaped glycoprotein spike which extends outwards from the viral envelope. . The long segment (around 7200 nucleotides in length) encodes the viral polymerase and a zinc-binding protein. The virus is spread by rodents. A member of the genus "Arenavirus", Junin virus characteristically
Junin virus
12418750
the CD4 molecule – a chemokine receptor – which is most commonly found on the surface of CD4+ T-Cells. This mechanism has evolved to favour those viruses that infect only cells in which they are capable of replication. Attachment to the receptor can induce the viral envelope protein to undergo changes that results in the fusion of viral and cellular membranes, or changes of non-enveloped virus surface proteins that allow the virus to enter. Penetration follows attachment: Virions enter the host cell through receptor-mediated endocytosis or membrane fusion. This is often called viral entry. The infection of plant and fungal
Virus
7300573
into the host cell is achieved by attachment of the viral envelope protein E to host receptors, which mediates clathrin-mediated endocytosis. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription is the method of transcription. Translation takes place by viral initiation. The virus exits the host cell by budding. Mammals serve as the natural host. Transmission routes are parental. "Pestivirus" viruses have a single strand of positive-sense RNA (i.e. RNA which can be directly translated into viral proteins) which is around 12.5 kilobases (kb) long (equal to the length of 12,500 nucleotides). Sometimes virions (individual
Pestivirus
10294185
Coronavirus packaging signal The Coronavirus packaging signal is a conserved cis-regulatory element found in Coronavirus which has an important role in regulating the packaging of the viral genome into the capsid. As part of the viral life cycle, within the infected cell, the viral genome becomes associated with viral proteins and assembles into new infective progeny viruses This process is called packaging and is vital for viral replication. This virus has positive-sense single-stranded RNA genome. A short region (190 base pairs) in the viral genome was identified that interacts with a viral envelope protein (protein M) and enables the viral
Coronavirus packaging signal
2584946
activity (used when the DNA genome is synthesized from pgRNA that was packaged in virions for replication to destroy the RNA template and produce the pdsDNA genome), and DNA-dependent-DNA-polymerase activity (used to create cccDNA from pdsDNA in the first step of the replication cycle). The hepatitis envelope proteins are composed of subunits made from the viral preS1, preS2, and S genes. The L (for "large") envelope protein contains all three subunits. The M (for "medium") protein contains only preS2 and S. The S (for "small") protein contains only S. The genome portions encoding these envelope protein subuntis share both the
Hepadnaviridae
11608759
an icosahedral nucleocapsid core composed of protein. These virions are 30–42 nm in diameter. The nucleocapsid encloses the viral DNA and a DNA polymerase that has reverse transcriptase activity. The outer envelope contains embedded proteins that are involved in viral binding of, and entry into, susceptible cells. The virus is one of the smallest enveloped animal viruses. The 42 nm virions, which are capable of infecting liver cells known as hepatocytes, are referred to as "Dane particles". In addition to the Dane particles, filamentous and spherical bodies lacking a core can be found in the serum of infected individuals. These
Hepatitis B
11813099
of the cell rather than in the nucleus. In order to replicate, poxviruses produce a variety of specialized proteins not produced by other DNA viruses, the most important of which is a viral-associated DNA-dependent RNA polymerase. Both enveloped and unenveloped virions are infectious. The viral envelope is made of modified Golgi membranes containing viral-specific polypeptides, including hemagglutinin. Infection with either variola major or variola minor confers immunity against the other. Transmission occurred through inhalation of airborne variola virus, usually droplets expressed from the oral, nasal, or pharyngeal mucosa of an infected person. It was transmitted from one person to another
Smallpox
6078760
the genome, non-structural and structural. The first is non structural and encodes proteins (nsP1–nsP4) necessary for transcription and replication of viral RNA. The second encodes three structural proteins: the core nucleocapsid protein C, and the envelope proteins P62 and E1 that associate as a heterodimer. The viral membrane-anchored surface glycoproteins are responsible for receptor recognition and entry into target cells through membrane fusion. The proteolytic maturation of P62 into E2 and E3 causes a change in the viral surface. Together the E1, E2, and sometimes E3, glycoprotein "spikes" form an E1/E2 dimer or an E1/E2/E3 trimer, where E2 extends from
Alphavirus
12941510
BoDV-1 p24 RNA has been detected in the peripheral blood mononuclear cells (PBMCs) of psychiatric patients with such conditions. Some studies find a significant difference in the prevalence of BDV p24 RNA in patients with mood disorders and schizophrenia, whilst others find no difference between patients and control groups. Consequently, debate about the role of BDV in psychiatric diseases remains alive. Bornaviruses enter host cells by endocytosis. The viral genome and associated viral proteins is released into the cytoplasm following fusion of the viral envelope and the endosome membrane. Replication of bornaviruses occurs inside the nucleus. These are the only
Borna disease virus
2825420
endosome, part of the haemagglutinin protein fuses the viral envelope with the vacuole's membrane, releasing the viral RNA (vRNA) molecules, accessory proteins and RNA-dependent RNA polymerase into the cytoplasm (Stage 2). These proteins and vRNA form a complex that is transported into the cell nucleus, where the RNA-dependent RNA polymerase begins transcribing complementary positive-sense cRNA (Steps 3a and b). The cRNA is either exported into the cytoplasm and translated (step 4), or remains in the nucleus. Newly synthesised viral proteins are either secreted through the Golgi apparatus onto the cell surface (in the case of neuraminidase and hemagglutinin, step 5b)
Orthomyxoviridae
5833876
becomes exposed and induces the fusion of the viral envelope with the membrane of the target cell.Another way that fuses the viral envelope to the host cell is with endocytic vesicles. HEF does not cleave the terminal silica acid residue from carbohydrates but removes the acetyl group from the position C9 of N-acetyl-9-O-acetylneuraminic acid. This is required to release fresh budded virus particles from infected cells, which otherwise would be trapped in the plasma membrane if the receptor is still present Influenza C is distinguishable from Influenza A and B by its structural components. There are three amino acids that
Hemagglutinin esterase
6196119
M1 protein The M1 protein is a matrix protein of the influenza virus. It forms a coat inside the viral envelope. This is a bifunctional membrane/RNA-binding protein that mediates the encapsidation of RNA-nucleoprotein cores into the membrane envelope. It is therefore required that M1 binds both membrane and RNA simultaneously. The M1 protein binds to the viral RNA. The binding is not specific to any RNA sequence, and is performed via a peptide sequence rich in basic amino acids. It also has multiple regulatory functions, performed by interaction with the components of the host cell. The mechanisms regulated include a
M1 protein
6196117
M1 protein The M1 protein is a matrix protein of the influenza virus. It forms a coat inside the viral envelope. This is a bifunctional membrane/RNA-binding protein that mediates the encapsidation of RNA-nucleoprotein cores into the membrane envelope. It is therefore required that M1 binds both membrane and RNA simultaneously. The M1 protein binds to the viral RNA. The binding is not specific to any RNA sequence, and is performed via a peptide sequence rich in basic amino acids. It also has multiple regulatory functions, performed by interaction with the components of the host cell. The mechanisms regulated include a
M1 protein
17276883
components of the virus like the capsid, the matrix, nucleoproteins. The "pol" domain codes for the reverse transcriptase and integrase enzymes. Lastly, the "env" domain of the viral genome encodes for the glycoproteins and envelope on the surface of the virus. There are multiple steps involved in the infection and replication of a lentivirus in a host cell. In the first step the virus uses its surface glycoproteins for attachment to the outer surface of a cell. More specifically, lentiviruses attach to the CD40 ligand glycoproteins on the surface of a hosts target cell. The viral material is then injected
Lentiviral vector in gene therapy
7111924
nucleocapsid shell and the viral envelope. The completed phage progeny remain in the cytosol until sufficient levels of the lytic protein P5 degrade the host cell wall. The cytosol then bursts forth, disrupting the outer membrane, releasing the phage. The bacterium is killed by this lysis. RNA-dependent RNA polymerases (RdRPs) are critical components in the life cycle of double-stranded RNA (dsRNA) viruses. However, it is not fully understood how these important enzymes function during viral replication. Expression and characterization of the purified recombinant RdRP of Φ6 is the first direct demonstration of RdRP activity catalyzed by a single protein from
Pseudomonas phage Φ6
3398631
horses. Several additional viruses in the genus have been described in bats and rodents. The hepatitis C virus particle consists of a lipid membrane envelope that is 55 to 65 nm in diameter. Two viral envelope glycoproteins, E1 and E2, are embedded in the lipid envelope. They take part in viral attachment and entry into the cell. Within the envelope is an icosahedral core that is 33 to 40 nm in diameter. Inside the core is the RNA material of the virus. E1 and E2 are covalently bonded when embedded in the envelope of HCV and are stabilized by disulfide
Hepatitis C virus
7601734
a compact conformation of the gB glycoprotein, so that it springs out and punctures the cell membrane. The envelope covering the virus particle then fuses with the cell membrane, creating a pore through which the contents of the viral envelope enters the host cell. The sequential stages of HSV entry are analogous to those of other viruses. At first, complementary receptors on the virus and the cell surface bring the viral and cell membranes into proximity. Interactions of these molecules then form a stable entry pore through which the viral envelope contents are introduced to the host cell. The virus
Herpes simplex virus
188429
consisting of three gp41 molecules that anchor the structure into the viral envelope. The Envelope protein, encoded by the HIV "env" gene, allows the virus to attach to target cells and fuse the viral envelope with the target cell's membrane releasing the viral contents into the cell and initiating the infectious cycle. As the sole viral protein on the surface of the virus, the Envelope protein is a major target for HIV vaccine efforts. Over half of the mass of the trimeric envelope spike is N-linked glycans. The density is high as the glycans shield the underlying viral protein from
HIV
2473336
phosphoprotein (P), matrix protein (M) and nucleoprotein (N): The VSIV G protein, aka VSVG, enables viral entry. It mediates viral attachment to an LDL receptor (LDLR) or an LDLR family member present on the host cell. Following binding, the VSIV-LDLR complex is rapidly endocytosed. It then mediates fusion of the viral envelope with the endosomal membrane. VSIV enters the cell through partially clathrin-coated vesicles; virus-containing vesicles contain more clathrin and clathrin adaptor than conventional vesicles. Virus-containing vesicles recruit components of the actin machinery for their interaction, thus inducing its own uptake. VSIV G does not follow the same path as
Vesicular stomatitis virus
7404514
weakened and shed more viral particles for an extended period. The lipid bilayer envelope of these viruses is relatively sensitive to desiccation, heat, and detergents, therefore these viruses are easier to sterilize than non-enveloped viruses, have limited survival outside host environments, and typically must transfer directly from host to host. Enveloped viruses possess great adaptability and can change in a short time in order to evade the immune system. Enveloped viruses can cause persistent infections. Classes of enveloped viruses that contain human pathogens: Classes of nonenveloped viruses that contain human pathogens: Viral envelope Some viruses (e.g. HIV and many animal
Viral envelope
11203109
create the virus's own viral envelope—is most effective for viruses that need an envelope in the first place. These include enveloped viruses such as HIV, HSV, SARS or smallpox. Prior to budding, the virus may put its own receptor onto the surface of the cell in preparation for the virus to bud through, forming an envelope with the viral receptors already on it. Though budding does not immediately destroy the host cell, this process will slowly use up the cell membrane and eventually lead to the cell's demise. This is also how antiviral responses are able to detect virus-infected cells.
Viral shedding
8341895
by which this barrier is breached depends upon the virus. Types of entry are: Through the use of green fluorescent protein (GFP), virus entry and infection can be visualized in real-time. Once a virus enters a cell, replication is not immediate and indeed takes some time (seconds to hours). The most well-known example is through membrane fusion. In viruses with a viral envelope, viral receptors attach to the receptors on the surface of the cell and secondary receptors may be present to initiate the puncture of the membrane or fusion with the host cell. Following attachment, the viral envelope fuses
Viral entry
8341896
with the host cell membrane, emptying the now-bare virus into the cell. In essence, the virus's envelope "blends" with the host cell membrane, releasing its contents into the cell. Obviously, this can only be done with viruses that have an envelope (examples of such enveloped viruses include HIV, KSHV and herpes simplex virus.) Viruses with no viral envelope enter the cell through endocytosis; they are ingested by the host cell through the cell membrane. In essence, the virus tricks the cell into thinking that the virus knocking at the door is nothing more than nutrition or harmless goods. A cell,
Viral entry
11953050
six subgroups, labelled A through E and J, each having a different antigenicity due to variances in viral envelope glycoproteins. Strains A through E are highly related and are believed to have evolved from the same ancestor. The subgroups evolved to utilize difference cellular receptors to gain entry into avian cells due to the host developing resistance to viral entry. Some antigenic variation can occur within subgroups, and all strains are oncogenic, but oncogenicity and the ability to replicate varies between subgroups. Like many retroviruses, ASLV consists of a lipid envelope containing transmembrane and cell surface glycoproteins. Enclosed within the
Avian sarcoma leukosis virus
4223546
not express early viral genes ORF36 – vPK – viral protein kinase with multiple roles in replication cycle ORF37 – SOX – dual function protein – DNase activity required for genome packaging and RNase activity regulates host gene expression ORF38 – involved in viral particle formation ORF39 – gM – envelope glycoprotein ORF40 and ORF41 – helicase and primase – DNA replication ORF42 – uncharacterized ORF45 - tegument protein, interacts with p90 ribosomal S6 kinases (RSKs) to modulate the ERK/RSK MAPK signaling pathway ORF47 – gL – envelope glycoprotein involved in viral entry ORF49 – may be required for viral
Kaposi's sarcoma-associated herpesvirus
2976411
in a manner analogous to peptidoglycan layer in other gram-negative bacteria. In the intracellular forms of the bacterium the disulfide cross linkage is not found, which confers this form more mechanically fragile. The cell envelopes of the bacterial class of mollicutes do not have a cell wall. The main pathogenic bacteria in this class are mycoplasma and ureaplasma. L-form bacteria are strains bacteria that lack cell walls derived from bacteria that normally possess cell walls. Viral envelope Cell envelope The cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In gram-negative bacteria an outer membrane
Cell envelope
1695168
with cellular MHC class II molecules. This triggers fusion of the viral envelope with the cell membrane, allowing EBV to enter the B cell. Human CD35, also known as complement receptor 1 (CR1), is an additional attachment factor for gp350/220, and can provide a route for entry of EBV into CD21-negative cells, including immature B-cells. EBV infection downregulates expression of CD35. To enter epithelial cells, viral protein BMRF-2 interacts with cellular β1 integrins. Then, viral protein gH/gL interacts with cellular αvβ6/αvβ8 integrins. This triggers fusion of the viral envelope with the epithelial cell membrane, allowing EBV to enter the epithelial
Epstein–Barr virus
6191722
the envelope. This envelope is then compared with the wheel housing and other components in the area to perform an interference/collision analysis. The results of this analysis tell the engineers whether that wheel/tire combo will strike the housing and components under normal driving conditions. If so, either a redesign is in order, or that wheel/tire combo will not be recommended. A different wheel envelope must be generated for each wheel/tire combo for which the vehicle is rated. Much of this analysis is done using CAD/CAE systems running on computers. Of course, high speed collisions, during an accident, are not considered
Envelope (motion)
18698402
viral and host cell's membranes, transcription of viral DNA and the integration of viral DNA into the genome of the host cell. For example, to prevent the fusion of the viral and host cell's membrane, monoclonal antibodies, which are virus entry inhibitors, can be placed into the human body to prevent the interaction between the CD4 receptors and the viral HIV envelope protein gp120. In addition, post-entry inhibitors can be placed into the body to block the virus once it has entered the host cell. To be utilized, post-entry inhibitors must be released when viral reverse transcriptase or viral integrase
Treatment as prevention
2222209
filter. The envelope detector has several drawbacks: Most of these drawbacks are relatively minor and are usually acceptable tradeoffs for the simplicity and low cost of using an envelope detector. An envelope detector can be used to demodulate a previously modulated signal by removing all high frequency components of the signal. The capacitor and resistor form a low-pass filter to filter out the carrier frequency. Such a device is often used to demodulate AM radio signals because the envelope of the modulated signal is equivalent to the baseband signal. An envelope detector is sometimes referred to as an envelope follower
Envelope detector
1307589
that challenging monkeys with a cytomegalovirus (CMV)-based SIV vaccine results in containment of virus. Typically, virus replication and dissemination occurs within days after infection, whereas vaccine-induced T cell activation and recruitment to sites of viral replication takes weeks. Researchers hypothesized that vaccines designed to maintain activated effector memory T cells might impair viral replication at its earliest stage. Several vaccine candidates are in varying phases of clinical trials. Most initial approaches have focused on the HIV envelope protein. At least thirteen different gp120 and gp160 envelope candidates have been evaluated, in the US predominantly through the AIDS Vaccine Evaluation Group.
HIV vaccine
14566376
that limits how rapidly it can vary with location r. In determining the behavior of the carriers using quantum mechanics, the "envelope approximation" usually is used in which the Schrödinger equation is simplified to refer only to the behavior of the envelope, and boundary conditions are applied to the envelope function directly, rather than to the complete wavefunction. For example, the wavefunction of a carrier trapped near an impurity is governed by an envelope function "F" that governs a superposition of Bloch functions: where the Fourier components of the envelope "F"(k) are found from the approximate Schrödinger equation. In some
Envelope (waves)
2664059
the presence or absence of glycosyltransferases which dictates which blood group antigens are presented and hence what antibody specificities are exhibited. This immunological role may well have driven the diversification of glycan heterogeneity and creates a barrier to zoonotic transmission of viruses. In addition, glycosylation is often used by viruses to shield the underlying viral protein from immune recognition. A significant example is the dense glycan shield of the envelope spike of the human immunodeficiency virus. Overall, glycosylation needs to be understood by the likely evolutionary selection pressures that have shaped it. In one model, diversification can be considered purely
Glycosylation
463892
serves as a molecular signal to stall the exonuclease and is the only viral requirement for subgenomic flavivirus RNA (sfRNA) production. The sfRNAs are a result of incomplete degradation of the viral genome by the exonuclease and are important for viral pathogenicity. Yellow fever belongs to the group of hemorrhagic fevers. The viruses infect, amongst others, monocytes, macrophages, and dendritic cells. They attach to the cell surface via specific receptors and are taken up by an endosomal vesicle. Inside the endosome, the decreased pH induces the fusion of the endosomal membrane with the virus envelope. The capsid enters the cytosol,
Yellow fever
597939
that have a lipid envelope must also fuse their envelope with the target cell, or with a vesicle that transports them into the cell, before they can uncoat. This stage of viral replication can be inhibited in two ways: This strategy of designing drugs can be very expensive, and since the process of generating anti-idiotypic antibodies is partly trial and error, it can be a relatively slow process until an adequate molecule is produced. A very early stage of viral infection is viral entry, when the virus attaches to and enters the host cell. A number of "entry-inhibiting" or "entry-blocking"
Antiviral drug
20414686
then lyses the endosome and virus, exposing the cytoplasm to viral nucleocapsid. Cholesterol is also necessary for the Alphavirus to undergo fusion. This fusion of the endosomal membrane to the viral envelope allows the release of nucleocapsid into the cytoplasm of the host cell. Almost immediately the nucleocapsid is uncoated, exposing the viral RNA to the host cytoplasm MIDV is a member of the Togovirdiae family which is hypothesized to use a "factory" replication process. The "factories" in this case, are the host cell's endosomes and lysosomes. The role of the endosome was explained above in the section on viral
Middelburg virus
10565446
cloning. Sendai virus induced cell fusion occurs in four different temperature stages. During the first stage, which lasts no longer than 10 minutes, viral adsorption takes place and the adsorbed virus can be inhibited by viral antibodies. The second stage, which is 20 minutes, is pH dependent and an addition of viral antiserum can still inhibit ultimate fusion. In the third, antibody-refractory stage, viral envelope constituents remain detectable on the surface of cells. During the fourth stage, cell fusion becomes evident and HA neuraminidase and fusion factor begin to disappear. The first and second stages are the only two that
Cell fusion
5115203
for the activation of many molecular components of the signaling cascade of an activated T cell. Depending on the signal, different types of T helper cells result. Phosphorylated ITAM motifs on CD3 recruit and activate SH2 domain-containing protein tyrosine kinases (PTK) such as Zap70 to further mediate downstream signalling through tyrosine phosphorylation, leading to transcription factor activation including NF-κB and consequent T cell activation. CD4 has also been shown to interact with SPG21, Lck and Protein unc-119 homolog. HIV-1 uses CD4 to gain entry into host T-cells and achieves this through its viral envelope protein known as gp120. The binding
CD4
2541327
Kip3), an ATP-dependent depolymerase, accelerate microtubule depolymerization at the plus end. It was shown the concurrent disruption of these mechanisms, but not of any one, results in dramatic spindle hyperstability during telophase, suggesting functional overlap despite the diversity of the mechanisms. The main components of the nuclear envelope are a double membrane, nuclear pore complexes, and a nuclear lamina internal to the inner nuclear membrane. These components are dismantled during prophase and prometaphase and reconstructed during telophase, when the nuclear envelope reforms on the surface of separated sister chromatids. The nuclear membrane is fragmented and partly absorbed by the endoplasmic
Telophase
7523396
glycoproteins allows them to escape the human body's immune system. In contrast to gp120, however, gp41 is less glycosylated and more conserved (less prone to genetic variations). Once gp160 has been cleaved into its individual subunits, the subunits are then associated non-covalently on the surface of the viral envelope. Gp41 and gp120, when non-covalently bound to each other, are referred to as the envelope spike complex and are formed as a heterotrimer of three gp41 and three gp120. These complexes found on the surface of HIV are responsible for the attachment, fusion, and ultimately the infection of host cells. The
Gp41
6178341
affect the fitness of the virus by providing more or less sensitivity to neutralizing antibodies. The presence of large carbohydrate chains extending from gp120 might obscure possible antibody binding sites. The boundaries of the potential to add and eliminate PNGSs are naively explored by growing viral populations following each new infection. While the transmitting host has developed a neutralizing antibody response to gp120, the newly infected host lacks immune recognition of the virus. Sequence data shows that initial viral variants in an immunologically naïve host have few glycosylation sites and shorter exposed variable loops. This may facilitate viral ability to
Envelope glycoprotein GP120
7817082
Polymyxin B is composed of polymyxins B1, B1-I, B2, B3, and B6. Polymyxins B1 and B2 are considered major components. These related components are structurally identical with the exception of a variable fatty acid group on each fraction. Results from in vitro studies have shown marginal differences in MIC data when comparing the fractions. In addition to its antibiotic function, polymyxin B has been used to clear endotoxin contamination in reagents. Polymyxin B is also used to induce envelope stress in order to study the organisms response to such stress. Polymyxin envelope stress assays such as this have been used
Polymyxin B
7842215
Evidence for this interaction was discovered in 2001 when a deliberate mutation for a conserved arginine (Arg) residue at position 50 to alanine of the SFVcpz inhibited proper capsid assembly and abolished viral budding even in the presence of the envelope glycoproteins. Analysis of the glycoproteins on the envelope of the viral particle indicate that it is localized to the endoplasmic reticulum (ER), and that once it buds from the organelle, the maturation process is finalized and can leave to infect additional cells. A dipeptide of two lysine residues (dilysine) was the identified motif that determined to be the specific
Simian foamy virus
6178343
easily detected by neutralizing antibodies. Therefore, a stabilizing selection balance between low and high glycan densities is likely established. A lower number of bulky glycans improves viral replication efficiency and higher number on the exposed loops aids host immune evasion via disguise. The relationship between gp120 and neutralizing antibodies is an example of Red Queen evolutionary dynamics. Continuing evolutionary adaptation is required for the viral envelope protein to maintain fitness relative to the continuing evolutionary adaptations of the host immune neutralizing antibodies, and vice versa, forming a coevolving system. Since CD4 receptor binding is the most obvious step in HIV
Envelope glycoprotein GP120
10321763
the viral envelope glycoprotein. A later study confirmed the findings that NPC1 is a critical filovirus receptor that mediates infection by binding directly to the viral envelope glycoprotein and that the second lysosomal domain of NPC1 mediates this binding. In one of the original studies, a small molecule was shown to inhibit Ebola virus infection by preventing the virus glycoprotein from binding to NPC1. In the other study, mice that were heterozygous for NPC1 were shown to be protected from lethal challenge with mouse adapted Ebola virus. Together, these studies suggest NPC1 may be potential therapeutic target for an Ebola
NPC1