Structure and product relationship analysis of acyl homoserine lactone synthases among Ensifer adhaerens reveals distinct chromosome and plasmid origins.

Despite the conservative DNA sequences among LuxI (Acyl Homoserine Lactones synthase gene) homologs, structure-product relationship of AHL synthase remains to be elucidated. In this study, through degenerate primers and in vitro expression methods, we collected the information of the gene sequences and AHL profiles from nine LuxIs among Ensifer adhaerens strains. The chromosome-encoded LuxI (C-LuxI) distinguished themselves from the plasmid-encoded ones (P-LuxI) not only in the DNA sequences, but also in AHL profiles. The C-LuxIs produced only C14-HSL, while the P-LuxIs produced predominantly C8-HSL and 3-oxo-C8-HSL. Sequence-product relationship analysis updated our recognition of the role of T140 (EsaI) in the 3-oxo-HSL production. Computational calculation based on 3D structures of these LuxIs revealed the linear relationship between the chain length and the affinity of amides to AHL synthase in C-LuxI, which was not found in the P-LuxI. We hereby proposed the linear docking affinity as a criterion for the prediction of long-chain AHL production by an AHL synthase. This study extends our understanding on the structure-product relationship of AHL synthases and revealed the distinct chromosome and plasmid origin of this enzyme among E. adhaerens.