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Biosynthesis of lipopolysaccharide O-antigens in Klebsiella pneumoniae

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Title: Biosynthesis of lipopolysaccharide O-antigens in Klebsiella pneumoniae
Author: Williams, Danielle
Department: Department of Molecular and Cellular Biology
Program: Molecular and Cellular Biology
Advisor: Whitfield, Chris
Abstract: Klebsiella pneumoniae is a leading cause of hospital and community acquired infections. Like other Gram-negative bacteria, K. pneumoniae isolates possess a characteristic cell envelope consisting of an inner and an outer membrane, where the outer membrane is an asymmetric lipid bilayer; the inner leaflet consists of phospholipids while the outer leaflet consists of lipopolysaccharide (LPS). The LPS consists of three structural regions: lipid A, core oligosaccharide, and O-antigenic polysaccharide (OPS). The OPS is hypervariable and differs in glycose and non-glycose components, linkages, and topology. OPS have been used for serological typing for epidemiological tracking and are important candidates for immunotherapeutic interventions. Despite their varied structures, all K. pneumoniae OPS are assembled via the same overall strategy. They are synthesized in the cytoplasm and exported via an ATP-binding cassette (ABC) transporter for ligation to lipid A-core in the periplasm. The focus of this thesis research is the biosynthesis of K. pneumoniae serotypes O12, O7, and O4. Using a combination of mutation and biochemical investigation of the activities of purified proteins, the essential components of the assembly pathways were identified. Central to the O12 and O7 pathways are modular proteins that encompass some or all of the activities required for glycan polymerization, chain termination, control of chain length, and export. WbbB, from K. pneumoniae O12, provides all the necessary activities in a single protein, while K. pneumoniae O7 requires two proteins to accomplish these processes. In contrast, K. pneumoniae O4 completes these steps using monofunctional proteins. The findings reported here provide new insight into the versatility of proteins involved in the assembly of bacterial polysaccharides in K. pneumoniae and other bacteria, in addition to identifying novel molecular strategies for producing glycan diversity.
Date: 2022-08
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Related Publications: Williams, D.M., O.G. Ovchinnikova, A. Koizumi, I.L. Mainprize, M.S. Kimber, T.L. Lowary, and C. Whitfield. 2017. Single polysaccharide assembly protein that integrates polymerization, termination, and chain-length quality control. Proc Natl Acad Sci U.S.A. 114:E1215–E1223. doi: 10.1073/pnas.1613609114.Whitfield, C., D.M. Williams, and S.D. Kelly. 2020b. Lipopolysaccharide O-antigens-bacterial glycans made to measure. J Biol Chem. 295:10593–10609. doi: 10.1074/jbc.REV120.009402.

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