N-Acyl homoserine lactones (Abbreviated as AHLs or N-AHLs) are a class of signaling molecules involved in bacterial quorum sensing, a means of communication between bacteria enabling behaviors based on population density. The first AHL (N-3-(oxo-hexanoyl)-homoserine lactone) was found as the natural inducer of bioluminescence in the bacterium Vibrio fischeri. Quorum sensing by the means of AHLs contributes to regulate the transcription of specific genes and therefore expression of specific phenotypes, including growth, virulence, biofilm formation, bioluminescence, production of exopolysaccharide (EPS). Over 50 gram-negative bacteria species (including several pathogenic species) use AHLs as autoinducers and the means of their communication in Quorum sensing. in one study, AHL was shown to interact with eukaryotic cells, and mitigate an immune response and facilitates infection. AHLs are one of the major groups of the autoinducer (AI) molecules which are found primarily in Gram-negative proteobacteria but also in some bacteriodetes, cyanobacteria, and archaea. The other two major groups are oligopeptides AIs in Gram-positive bacteria; and autoinducer-2 (AI-2), a as a universal signal for interspecies communications. Formation It arises by the reaction of acyl carrier proteins react with S-adenosylmethionine. The latter donates the equivalent of 4-aminobutyrolactone. Methylthioadenosine is a coproduct. Homoserine lactone is also a product of the proteolytic reaction of cyanogen bromide (CNBr) with a methionine residue. This reaction is important for chemical sequencing of proteins. Structure AHLs have hydrophobic and hydrophilic sections. The hydrophilic section consists of the homoserine lactone ring and the amide group. The hydrophobic section has a strain-specific hydrocarbon chain with varieties in length and level of oxygenation with a 3-oxo group. The length of the acyl chain generally ranges from 4 to 18 carbons. The length of R-group side-chain variable. Chain lengths vary from 4 to 18 carbon atoms and in the substitution of a carbonyl at the third carbon.The hydrophilic sections form a hydrogen bonded network within the receptor binding site, while the hydrophobic sites contribute to diffusional and binding properties within the hydrophobic pocket. Studies have not yet demonstrated a correlation between the AHL synthase enzymes and AHL type. LuxI protein synthesizes an acylated homoserin-lactone molecule. The LuxI gene is highly conserved, which indicates that although diverse, there are a limited number of AHL-type signals that are produced by bacteria. However, in the AHL synthase enzyme family, the C-terminal region, which determines the type of substrates the synthetase can recognize and the subsequent acyl-chain length, is not conserved.