Taxonomic group: bacteria / Proteobacteria
(Phylum: Proteobacteria)
Host organism: Homo sapiens
Associated disease: typhoid fever [ICD11:
1A07 
, ICD11:
XN4AM ];
infection due to Salmonella enterica [ICD11:
XN5VC ]
NCBI PubMed ID: 27226298Publication DOI: 10.1073/pnas.1524665113Journal NLM ID: 7505876Publisher: National Academy of Sciences
Correspondence: cwhitfie
uoguelph.ca
Institutions: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada, N1G2W1
Polysaccharide capsules are surface structures that are critical for the virulence of many Gram-negative pathogenic bacteria. Salmonella enterica serovar Typhi is the etiological agent of typhoid fever. It produces a capsular polysaccharide known as 'Vi antigen,' which is composed of nonstoichiometrically O-acetylated α-1,4-linked N-acetylgalactosaminuronic acid residues. This glycan is a component of currently available vaccines. The genetic locus for Vi antigen production is also present in soil bacteria belonging to the genus Achromobacter Vi antigen assembly follows a widespread general strategy with a characteristic glycan export step involving an ATP-binding cassette transporter. However, Vi antigen producers lack the enzymes that build the conserved terminal glycolipid characterizing other capsules using this method. Achromobacter species possess a Vi antigen-specific depolymerase enzyme missing in S enterica Typhi, and we exploited this enzyme to isolate acylated Vi antigen termini. Mass spectrometry analysis revealed a reducing terminal N-acetylhexosamine residue modified with two beta-hydroxyl acyl chains. This terminal structure resembles one half of lipid A, the hydrophobic portion of bacterial lipopolysaccharides. The VexE protein encoded in the Vi antigen biosynthesis locus shares similarity with LpxL, an acyltransferase from lipid A biosynthesis. In the absence of VexE, Vi antigen is produced, but its physical properties are altered, its export is impaired, and a Vi capsule structure is not assembled on the cell surface. The structure of the lipidated terminus dictates a unique assembly mechanism and has potential implications in pathogenesis and vaccine production.
Salmonella, Salmonella enterica, glycolipid, polysaccharide export, polysaccharide capsule, Vi antigen
Structure type: homopolymer
Location inside paper: abstract, p.6719
Trivial name: Vi-antigen, Vi antigen, Vi polysaccharide, Vi-antigen (glycotope)
Compound class: CPS
Contained glycoepitopes: IEDB_144984,IEDB_164179,IEDB_164180,IEDB_164181
Methods: 13C NMR, DNA sequencing, SDS-PAGE, sugar analysis, acid hydrolysis, Western blotting, MS/MS, de-O-acetylation, genetic methods, HPLC, GPC, electron microscopy, CD, LC-MS, bioinformatic analysis, immunofluorescence microscopy, LC-ESI-QTOF MS/MS
Biosynthesis and genetic data: genetic data
Related record ID(s): 11693, 11694
NCBI Taxonomy refs (TaxIDs): 90370Reference(s) to other database(s): GTC:G67538LH
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There is only one chemically distinct structure:
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(previously named: Salmonella typhi, NEW: Salmonella enterica ssp. enterica sv. Typhi)