Structural Basis of Low-Molecular-Weight Thiol Glycosylation in Lincomycin A Biosynthesis

The involvement of low-molecular-weight thiols in thebiosynthesisof natural products is rarely reported. During lincomycin A biosynthesis,ergothioneine (EGT) is incorporated in the S-glycosylationcatalyzed by LmbT. In contrast to the widely reported glycosylationof nitrogen and oxygen atoms, the glycosylation of sulfur atoms isless studied. In particular, the crystal structure of enzymes thatglycosylate thiols on small molecules rather than peptides has notbeen reported. Here, we report the crystal structures of LmbT in apo form and in complex with GDP and EGT S-conjugated lincosamine. We found that LmbT has a characteristicglycosyltransferase type B fold, which forms a symmetric homotetramer.The substrates are bound deeply in the catalytic cleft. Consistentwith the substrate structure, LmbT does not have the large peptidebinding groove of the previously reported S-glycosyltransferase.Combined with site-directed mutagenesis, we propose a catalytic mechanismfor the unusual EGT-mediated S-glycosylation in naturalproduct biosynthesis.

Automated summary

In this study, we report the crystal structures of LmbT in the S-glycosylation of EGT during lincomycin A biosynthesis. We found that LmbT has a characteristic glycosyltransferase type B fold and forms a symmetric homotetramer. The substrates are deeply bound in the catalytic cleft. Site-directed mutagenesis was performed to propose a catalytic mechanism for the unusual EGT-mediated S-glycosylation.