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Glycobiology Advance Access published online on March 12, 2008
Glycobiology, doi:10.1093/glycob/cwn021
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

A Unique Glycosyltransferase Involved in the Initial Assembly of Moraxella catarrhalis Lipooligosaccharides

Johanna M. Schwingel1,2,, Frank St. Michael5, Andrew D. Cox5, Hussein Masoud5, James C. Richards5 and Anthony A. Campagnari1,2,3,4,*

1 Department of Microbiology and Immunology, State University of New York at Buffalo, Buffalo, NY, 14214 USA
2 Witebsky Center for Microbial Pathogenesis and Immunology, State University of New York at Buffalo, Buffalo, NY, 14214 USA
3 Department of Medicine, State University of New York at Buffalo, Buffalo, NY, 14214 USA
4 New York State Center of Excellence in Bioinformatics & Life Sciences, State University of New York at Buffalo, Buffalo, NY, 14214 USA
5 Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6 Canada

* Corresponding Author. Mailing address: Department of Microbiology and Immunology, University at Buffalo, Biomedical Research Bldg. Rm. 143, 3435 Main St., Buffalo, NY 14214 USA; Phone: (716) 829-2673, Fax: (716) 829-3889, E-mail: aac{at}buffalo.edu

Received on October 9, 2007; accepted on March 2, 2008

Moraxella catarrhalis express three predominant forms of lipooligosaccharide (LOS) molecules on the bacterial surface. These major glycolipids contain specific carbohydrate epitopes that distinguish each glycoform into serotype A, B, or C LOS. All three serotypes, however, share a common glucose containing inner-core structure, consisting of an {alpha}-glucose attached to 2-keto-3-deoxyoctulosonic acid (KDO), which is unique among Gram-negative bacteria. Many of the LOS glycosyltransferase genes (lgt) responsible for assembly of the extended M. catarrhalis LOS structure have been identified. In this report, we now describe the identification and characterization of Lgt6, a unique glycosyltransferase that is responsible for the addition of the first glucose to the inner core thus initiating the assembly of full length LOS. Isogenic mutants defective in the expression of lgt6 were constructed in all three M. catarrhalis LOS serotypes and the resulting LOS glycoforms consisted of KDO2-lipidA-OH as analyzed by urea SDS-PAGE and mass spectrometry. In addition, the expression of lgt6 in trans in a heptose deficient Neisseria meningitidis NMB gmhX mutant resulted in the addition of a hexose to the LOS of this strain. These studies demonstrate that Lgt6 functions as an {alpha}–(1–5)-glucosyltransferase in M. catarrhalis adding the primary glucose to the KDO2-lipidA-OH in LOS biosynthesis. The function of Lgt6 is required for the completion of both the major and minor oligosaccharide chains in M. catarrhalis.

Key words: glycosyltransferase / lipooligosaccharide (LOS) / Moraxella catarrhalis


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