Phytopathogenic cyclic glucohexadecaose from an inverting transglycosylase

Abstract

AbstractXanthomonasspecies contain numerous notoriously well-known plant pathogens. Among various pathogenic factors, the role of α-1,6-cyclized β-1,2-glucohexadecaose (CβG16α) produced byXanthomonas campestrispv.campestriswas shown previously to be vital for infecting model organismsArabidopsis thalianaandNicotiana benthamiana. However, enzymes responsible for biosynthesising CβG16α are essentially unknown, which limits the generation of agrichemicals that inhibit CβG16α synthesis. In this study, we discovered that OpgD fromX. campestrispv.campestrisconverts linear β-1,2-glucan to CβG16α. Structural and functional analyses revealed that OpgD fromX. campestrispv.campestrispossesses an anomer-inverting transglycosylation mechanism, which is unprecedented among carbohydrate-active enzymes. The discovery of this unprecedented glucan-generating mechanism reveals a new foundation for the enzymatic synthesis of carbohydrates. Furthermore, identifying CβG16α synthase highly conserved inXanthomonasprovides a broadly adaptable drug target for new-genre agrichemicals that overcome antimicrobial-resistant bacterial issues.