Phylogenetic And Catalytic Mechanism Analysis Of Antibiotic Glycosyltransferases

Catalyzed by a family of enzymes called glycosyltransferases, glycosylation reactions are essential for the bioactivities of secondary metabolites such as antibiotics. Due to the special characters of antibiotic glycosyltransferases (AGts), antibiotics can function by attaching some unusual deoxy-sugars to their aglycons. Comprehensive similarity searches on the amino acid sequences of AGts have been performed. This paper reconstructed the molecular phylogeny of AGts with neighbor-joining, maximum-likelihood and Bayesian methods of phylogenetic inference. The phylogenetic trees show a distinct separation of polyene macrolide (PEM) AGts and other polyketide AGts. The former are more like eukaryotic glycosyltransferases and were deduced to be the results of horizontal gene transfer (HGT) from eukaryotes. This conclusion was also supported by structure-based phylogenetic analysis. Protein tertiary structural comparison indicated that some glycopeptide AGts (Gtf-proteins) have a close evolutionary relationship with MurGs, essential glycosyltransferases involved in maturation of bacterial cell walls. The evolutionary relationship of glycopeptide antibiotic biosynthetic gene clusters was speculated according to the phylogenetic analysis of Gtf-proteins. Based on the structural alignment of glycosyltransferases, the structurally homologous sites were detected, whose biological functions were also presumed. Considering the fact that polyketide AGts and Gtf-proteins are all GT-1 members and their aglycon acceptor biosynthetic patterns are very similar, this paper deduced that AGts and the synthases of their aglycon acceptors have some evolutionary relevancy. Finally, the evolutionary origins of AGts that do not fall under GT-1 (non-GT1 AGts) were discussed, suggesting that their ancestral proteins appear to be derived from various proteins responsible for primary metabolisms.