Structural Basis of Acyl-homoserine Lactone-Dependent Signaling

Acyl-homoserine lactones are small neutral lipid molecules that bacteria in the Proteobacteria group use to sense and signal their cell density. The production of AHL signals is regulated in different ways in a variety of organisms. In some organisms, such as Pantoea stewartii, the AHL synthase gene is constitutively expressed. AHL signaling can be terminated actively or passively, because AHLs are susceptible to degradation by both chemical and enzymatic means. The most recent discovery of a homoserine lactone-based signaling molecule comes from the plant symbiont Rhodopseudomonas palustris. X-ray crystallographic structural analyses of two of the LuxI-type AHL synthases provided the foundation of the current molecular understanding of AHL synthesis. The second part of the reaction mechanism is the cyclization of the methionine moiety of SAM, which gives rise to the lactone portion of the AHL and occurs through a lactonization reaction.