A Membrane-located Glycosyltransferase Complex Required for Biosynthesis of the d-Galactan I Lipopolysaccharide O Antigen in Klebsiella pneumoniae |
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Authors: | Veronica Kos Chris Whitfield |
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Institution: | From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada |
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Abstract: | d-Galactan I is a polysaccharide with the disaccharide repeat unit structure →3-β-d-Galf-(1→3)-α-d-Galp-(1→]. This glycan represents the lipopolysaccharide O antigen found in many Gram-negative bacteria, including several Klebsiella pneumoniae O serotypes. The polysaccharide is synthesized in the cytoplasm prior to its export via an ATP-binding cassette transporter. Sequence analysis predicts three galactosyltransferases in the d-galactan I genetic locus. They are WbbO (belonging to glycosyltransferase (GT) family 4), WbbM (GT-family 8), and WbbN (GT-family 2). The WbbO and WbbM proteins are each predicted to contain two domains, with the GT modules located toward their C termini. The N-terminal domains of WbbO and WbbM exhibit no similarity to proteins with known function. In vivo complementation assays suggest that all three glycosyltransferases are required for d-galactan I biosynthesis. Using a bacterial two-hybrid system and confirmatory co-purification strategies, evidence is provided for protein-protein interactions among the glycosyltransferases, creating a membrane-located enzyme complex dedicated to d-galactan I biosynthesis. |
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Keywords: | ABC Transporter Bacteria Carbohydrate Biosynthesis Lipopolysaccharide (LPS) Membrane Biogenesis Membrane Function Polysaccharide O Antigens Glycosyltransferases Prokaryotic Glycobiology |
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