The HS:1 serostrain ofCampylobacter jejunihas a complex teichoic acid‐like capsular polysaccharide with nonstoichiometric fructofuranose branches andO‐methyl phosphoramidate groups

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Abstract
Recently, the CPS biosynthetic loci for several strains ofCampylobacter jejuniwere sequenced and revealed evidence for multiple mechanisms of structural variation. In this study, the CPS structure for the HS:1 serostrain ofC. jejuniwas determined using mass spectrometry and NMR at 600 MHz equipped with an ultra‐sensitive cryogenically cooled probe. Analysis of CPS purified using a mild enzymatic method revealed a teichoic acid‐like [‐4)‐α‐d‐Galp‐(1–2)‐(R)‐Gro‐(1‐P]n, repeating unit, where Gro is glycerol. Two branches at C‐2 and C‐3 of galactose were identified as β‐d‐fructofuranoses substituted at C‐3 with CH3OP(O)(NH2)(OR) groups. Structural heterogeneity was due to nonstoichiometric glycosylation at C‐3 of galactose and variable phosphoramidate groups. Identical structural features were found for cell‐bound CPS on intact cells using proton homonuclear and31P heteronuclear two‐dimensional HR‐MAS NMR at 500 MHz. In contrast, spectroscopic data acquired for hot water/phenol purified CPS was complicated by the hydrolysis and subsequent loss of labile groups during extraction. Collectively, the results of this study established the importance of using sensitive isolation techniques and HR‐MAS NMR to examine CPS structuresin vivowhen labile groups are present. This study uncovered how incorporation of variableO‐methyl phosphoramidate groups on nonstoichiometric fructose branches is used inC. jejuniHS:1 as a strategy to produce a highly complex polysaccharide from its small CPS biosynthetic locus and a limited number of sugars.