exposed to low pH. This acidic environment causes a conformational change in the E protein, which disassociates it from the prM protein and causes it to form E homodimers, which lie flat against the viral surface, giving the maturing virion a smooth appearance. During this maturation, pr peptide is cleaved from the M peptide by the host protease, furin. The M protein then acts as a transmembrane protein under the E-protein shell of the mature virion. The pr peptide stays associated with the E protein until the viral particle is released into the extracellular environment. This pr peptide acts like a cap, covering the hydrophobic fusion loop of the E protein until the viral particle has exited the cell. NS3 protein The DENV NS3 is a serine protease, as well as an RNA helicase and RTPase/NTPase. The protease domain consists of six β-strands arranged into two β-barrels formed by residues 1–180 of the protein. The catalytic triad (His-51, Asp-75 and Ser-135) is found between these two β-barrels, and activity is dependent on the presence of a 43 amino acid segment of the NS2B cofactor. This cofactor wraps around the NS3 protease domain and becomes part of the active site. The remaining NS2B residues before and after the cofactor region contain helical domains involved in membrane binding. The remaining NS3 residues (180–618) form the three subdomains of the DENV helicase. A six-stranded parallel β-sheet surrounded by four α-helices makes up subdomains I and II, and subdomain III is composed of four α-helices surrounded by three shorter α-helices and two antiparallel β-strands. NS4A protein DENV NS4A is a nonstructural protein involved in altering cell membrane curvature and induction of autophagy. In addition to its membrane altering property, NS4A is a scaffold for the virus replication complex and undergoes oligomerization. Mutations of NS4A that affect interaction with NS4B abolished or severely reduced virus replication indicating the importance of NS4A and its interaction with NS4B in dengue reproduction. NS5 protein The DENV NS5 protein is a 900-residue peptide with a methyltransferase domain at its N-terminal end (residues 1–296) and a RNA-dependent RNA polymerase (RdRp) at its C-terminal end (residues 320–900). The methyltransferase domain consists of an α/β/β sandwich flanked by N-and C-terminal subdomains. The DENV RdRp is similar to other RdRps containing palm, finger, and thumb subdomains and a GDD motif for incorporating nucleotides. Complexes between the E protein and neutralizing antibodies Crystal structures