Three- component systems represent a common pathway for extracytoplasmic addition of pentofuranose sugars into bacterial glycans

• 成果类型: Article
• 署名作者: Kelly, Steven D.; Ha Duong, Nam; Nothof, Jeremy T.; Lowary, Todd L.; Whitfield, Chris
• 署名单位: University of Guelph; Academia Sinica - Taiwan; Academia Sinica - Taiwan; National Tsing Hua University; University of Alberta; National Taiwan University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-9319
• DOI: 10.1073/pnas.2402554121
• 发表日期: 2024-05-21
• 关键词: lipopolysaccharide o-antigens; escherichia-coli; dppr synthase; gene-cluster; biosynthesis; expression; polysaccharide; salmonella; identification; glucosylation

摘要

Cell surface glycans are major drivers of antigenic diversity in bacteria. The biochemistry and molecular biology underpinning their synthesis are important in understanding host-pathogen interactions and for vaccine development with emerging chemoenzymatic and glycoengineering approaches. Structural diversity in glycostructures arises from the action of glycosyltransferases (GTs) that use an immense catalog of activated sugar donors to build the repeating unit and modifying enzymes that add further heterogeneity. Classical Leloir GTs incorporate alpha- or beta- linked sugars by inverting or retaining mechanisms, depending on the nucleotide sugar donor. In contrast, the mechanism of known ribofuranosyltransferases is confined to beta- linkages, so the existence of alpha- linked ribofuranose in some glycans dictates an alternative strategy. Here, we use Citrobacter youngae O1 and O2 lipopolysaccharide O antigens as prototypes to describe a widespread, versatile pathway for incorporating side - chain alpha- linked pentofuranoses by extracytoplasmic postpolymerization glycosylation. The pathway requires a polyprenyl phosphoribose synthase to generate a lipid - linked donor, a MATE - family flippase to transport the donor to the periplasm, and a GT - C type GT (founding the GT136 family) that performs the final glycosylation reaction. The characterized system shares similarities, but also fundamental differences, with both cell wall arabinan biosynthesis in mycobacteria, and periplasmic glucosylation of O antigens first discovered in Salmonella and Shigella . The participation of auxiliary epimerases allows the diversification of incorporated pentofuranoses. The results offer insight into a broad concept in microbial glycobiology and provide prototype systems and bioinformatic guides that facilitate discovery of further examples from diverse species, some in currently unknown glycans.