N-hexanoyl-L-homoserine lactone (C6-HSL) is a quorum sensing signaling molecule produced by certain Gram-negative bacteria, including species of Vibrio and Pseudomonas. This molecule enables bacterial populations to communicate and coordinate behaviors such as biofilm formation, virulence, and motility. The biosynthesis of C6-HSL is catalyzed by an acyl-homoserine lactone synthase enzyme, such as LuxI or its homologs. The process begins with L-homoserine, which serves as the backbone for the molecule. A fatty acyl group, specifically a hexanoyl group derived from hexanoyl-CoA, is transferred to L-homoserine by the synthase enzyme, forming an amide bond. This intermediate is then cyclized to produce C6-HSL. Additionally, during this process, N-(3-oxohexanoyl)-L-homoserine lactone (3-oxo-C6-HSL) is also produced, which results from the modification of the hexanoyl group by the addition of a keto group at the C-3 position, catalyzed by some LuxI homologs that incorporate a 3-oxo group into the acyl chain. Both C6-HSL and 3-oxo-C6-HSL are quorum sensing molecules that diffuse out of the bacterial cell into the surrounding environment. As the bacterial population grows, the concentration of these signaling molecules increases. When they reach a critical threshold, they bind to a receptor protein such as LuxR, forming a C6-HSL-LuxR or 3-oxo-C6-HSL-LuxR complex that activates the transcription of quorum sensing-regulated genes. This system enables bacteria to synchronize their actions in response to population density, influencing processes such as pathogenicity, surface colonization, and resource utilization.

Quorum sensing: N-hexanoyl-L-homoserine lactone (C6-HSL) and N-(3-oxohexanoyl)-L-homoserine lactone Biosynthesis References