We report isolation and characterization of Campylobacter jejuni 81-176 lgtF and galT lipooligosaccharide (LOS) core mutants. It has been suggested that the lgtF gene of C. jejuni encodes a two-domain glucosyltransferase that is responsible for the transfer of a -1,4-glucose residue on heptosyltransferase I (Hep I) and for the transfer of a -1,2-glucose residue on Hep II. A site-specific mutation in the lgtF gene of C. jejuni 81-176 resulted in expression of a truncated LOS, and complementation of the mutant in trans restored the core mobility to that of the wild type. Mass spectrometry and nuclear magnetic resonance of the truncated LOS confirmed the loss of two glucose residues, a -1,4-glucose on Hep I and a -1,2-glucose on Hep II. Mutation of another gene, galT, encoding a glycosyltransferase, which maps outside the region defined as the LOS biosynthetic locus in C. jejuni 81-176, resulted in loss of the -(1,4)-galactose residue and all distal residues in the core. Both mutants invaded intestinal epithelial cells in vitro at levels comparable to the wild-type levels, in marked contrast to a deeper inner core waaC mutant. These studies have important implications for the role of LOS in the pathogenesis of Campylobacter-mediated infection.
FIG. 6. 1 H-NMR spectrum of C. jejuni 81-176 galT core OS. The spectrum shows two ␣-anomeric resonances of LD-Hep units (A and B) and two -anomeric resonances of Glc units (C and D); the deoxy signals of the Kdo unit and the methylene resonances of the PEA moiety are also evident. The inset shows the anomeric region of the 1 H-NMR spectrum obtained at 35°C to reveal anomeric resonance C, which coresonates with the HOD peak at 21°C. No GalNAc N-acetyl resonances were detected.
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