Homologous relationship between FabG involved in fatty acid biosynthesis and SDR on chromosome II in the multi-chromosome pathogen Vibrio anguillarum.

Vibrio anguillarum threatens fish and larval farming industries and human health worldwide. The identification of bacterial adaptation and responses to stress due to environmental changes is vital for establishing a response strategy for pathogenic Vibrio. Previously, short-chain dehydrogenase/reductase (SDR) was identified on chromosome II of the multichromosomal V. anguillarum. In this study, a comparison of SDR and the enzyme FabG-1b (encoded on chromosome I and responsible for the β-ketoacyl acyl carrier protein (ACP) reductase in fatty acid biosynthesis (FAS II)) showed that the amino acid sequence homology was only 33.2%; however, the core of functionality, which includes the NAD(P)-binding domain and the conserved region of the active site, the topologies predicted using sequence-based homology modeling, and the quaternary homotetramer-type structures showed a significant similarity. FabG-1b was specific to the substrates fluorinated and halogenated aliphatic ketones, aromatic ketones, and aromatic β-ketoesters and SDR toward non-fluorinated and non-halogenated aliphatic ketones, aromatic ketones, and non-aromatic β-ketoesters. This complementary catalytic efficiencies of the two enzymes on various substrates conclusively supports the hypothesis that the two enzymes are likely homologs. This is the first study to report potential paralogous enzymes FabG-1b and SDR in Vibrio. This information improves our understanding of bacterial FAS for establishing strategies to overcome infectious diseases caused by pathogenic strains and identify targets for developing new antibacterial agents.