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标题：Single polysaccharide assembly protein that integrates polymerization, termination, and chain-length quality control
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作者：Danielle M. Williams ; Olga G. Ovchinnikova ; Akihiko Koizumi 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2017
卷号：114
期号：7
页码：E1215-E1223
DOI：10.1073/pnas.1613609114
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Lipopolysaccharides (LPS) are essential outer membrane glycolipids in most gram-negative bacteria. Biosynthesis of the O-antigenic polysaccharide (OPS) component of LPS follows one of three widely distributed strategies, and similar processes are used to assemble other bacterial surface glycoconjugates. This study focuses on the ATP-binding cassette (ABC) transporter-dependent pathway, where glycans are completed on undecaprenyl diphosphate carriers at the cytosol:membrane interface, before export by the ABC transporter. We describe Raoultella terrigena WbbB, a prototype for a family of proteins that, remarkably, integrates several key activities in polysaccharide biosynthesis into a single polypeptide. WbbB contains three glycosyltransferase (GT) modules. Each of the GT102 and GT103 modules characterized here represents a previously unrecognized GT family. They form a polymerase, generating a polysaccharide of [4)-α-Rha p -(1→3)-β-Glc p NAc-(1→] repeat units. The polymer chain is terminated by a β-linked Kdo (3-deoxy- d - manno -oct-2-ulosonic acid) residue added by a third GT module belonging to the recently discovered GT99 family. The polymerase GT modules are separated from the GT99 chain terminator by a coiled-coil structure that forms a molecular ruler to determine product length. Different GT modules in the polymerase domains of other family members produce diversified OPS structures. These findings offer insight into glycan assembly mechanisms and the generation of antigenic diversity as well as potential tools for glycoengineering.
关键词：microbial glycobiology ; lipopolysaccharides ; glycosyltransferases ; glycan biosynthesis ; molecular ruler