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Taxonomic group: bacteria / Proteobacteria (Phylum: Proteobacteria)
Associated disease: infection due to Salmonella enterica [ICD11: XN5VC

]

NCBI PubMed ID: 36152747
Publication DOI: 10.1016/j.jbc.2022.102520
Journal NLM ID: 2985121R
Publisher: Baltimore, MD: American Society for Biochemistry and Molecular Biology
Correspondence: C. Whitfield <cwhitfie

uoguelph.ca>
Institutions: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada

i antigen is an extracellular polysaccharide produced by Salmonella enterica Typhi, Citrobacter freundii, and some soil bacteria belonging to the Burkholderiales. In Salmonella Typhi, Vi-antigen capsule protects the bacterium against host defenses, and the glycan is used in a current glycoconjugate vaccine to protect against typhoid. Vi antigen is a glycolipid assembled in the cytoplasm and translocated to the cell surface by an export complex driven by an ABC transporter. In Salmonella Typhi, efficient export and cell-surface retention of the capsule layer depend on a reducing terminal acylated-HexNAc moiety. Although the precise structure and biosynthesis of the acylated terminus has not been resolved, it distinguishes Vi antigen from other known glycolipid substrates for bacterial ABC transporters. The genetic locus for Vi antigen-biosynthesis encodes a single acyltransferase candidate (VexE), which is implicated in the acylation process. Here, we determined the structure of the VexE in vitro reaction product by mass spectrometry and NMR spectroscopy to reveal that VexE catalyzes β-hydroxyacyl-ACP dependent acylation of the activated sugar precursor, uridine-5'-diphospho-GlcNAc, at C-6 to form UDP-6-O-[β-hydroxymyristoyl]-α-d-GlcNAc. VexE belongs to the lysophosphatidyl acyltransferase family, and comparison of an Alphafold VexE model to solved lysophosphatidyl acyltransferase structures, together with modeling enzyme:substrate complexes, led us to predict an enzyme mechanism. This study provides new insight into Vi terminal structure, offers a new model substrate to investigate the mechanism of glycolipid ABC transporters, and adds biochemical understanding for a novel reaction used in the synthesis of an important bacterial virulence factor.

structure, NMR spectroscopy, mass spectrometry, capsule, glycolipid, Vi antigen, acyltransferase (VexE)

Structure type: homopolymer
Location inside paper: p. 102520-1
Trivial name: Vi-antigen, Vi antigen, Vi polysaccharide, Vi-antigen (glycotope)
Compound class: CPS
Contained glycoepitopes: IEDB_144984

Methods: 13C NMR, 1H NMR, NMR-2D, SDS-PAGE, DNA techniques, TLC, 31P NMR, ESI-MS, biochemical methods, HPLC, immunoblotting, HPLC-MS, bioinformatic analysis (BLASTp), IMAC, AEC, VexE acyltransferase assay
3D data: molecular modeling

NCBI Taxonomy refs (TaxIDs): 90370
Reference(s) to other database(s): GTC:G67538LH
Show glycosyltransferases

There is only one chemically distinct structure:

*O[C@H]1[C@@H](C(=O)O)O[C@H](*)[C@H](NC(C)=O)[C@H]1OC(C)=O

SVG MW SMILES 3D mol Ionize

Taxonomic group: fungi / Basidiomycota (Phylum: Basidiomycota)
Organ / tissue: capsule
Associated disease: infection due to Cryptococcus neoformans [ICD11: XN3EH

]

NCBI PubMed ID: 19542308
Publication DOI: 10.1128/EC.00013-09
Journal NLM ID: 101130731
Publisher: American Society for Microbiology
Correspondence: de Cock H <h.decock

uu.nl>
Institutions: Microbiology, Institute of Biomembranes, Department of BiologyUtrecht University, CH Utrecht, The Netherlands, Bio-Organic Chemistry, Bijvoet Center, Department of Chemistry, Utrecht University, Utrecht, The Netherlands, Microbiology, Institute of Biomembranes, CH Utrecht, The Netherlands

The human pathogen Cryptococcus neoformans causes meningoencephalitis. The polysaccharide capsule is one of the main virulence factors and consists of two distinct polysaccharides, glucuronoxylomannan (GXM) and galactoxylomannan (GalXM). How capsular polysaccharides are synthesized, transported, and assembled is largely unknown. Previously, it was shown that mutations in the CAP10, CAP59, CAP60, and CAP64 genes result in an acapsular phenotype. Here, it is shown that these acapsular mutants do secrete GalXM and GXM-like polymers. GXM and GalXM antibodies specifically reacted with whole cells and the growth medium of the wild type and CAP mutants, indicating that the capsule polysaccharides adhere to the cell wall and are shed into the environment. These polysaccharides were purified from the medium, either with or without anion-exchange chromatography. Monosaccharide analysis of polysaccharide fractions by gas-liquid chromatography/mass spectrometry showed that wild-type cells secrete both GalXM and GXM. The CAP mutants, on the other hand, were shown to secrete GalXM and GXM-like polymers. Notably, the GalXM polymers were shown to contain glucuronic acid. One-dimensional (1)H nuclear magnetic resonance confirmed that the CAP mutants secrete GalXM and also showed the presence of O-acetylated polymers. This is the first time it is shown that CAP mutants secrete GXM-like polymers in addition to GalXM. The small amount of this GXM-like polymer, 1 to 5% of the total amount of secreted polysaccharides, may explain the acapsular phenotype

Cryptococcus neoformans, Glucuronoxylomannan

Structure type: suggested polymer biological repeating unit ; 1000000-7000000
Location inside paper: fig. 1 (GXM)
Compound class: glucuronoxylomannan
Contained glycoepitopes: IEDB_114701,IEDB_115136,IEDB_115576,IEDB_130701,IEDB_140116,IEDB_140630,IEDB_144983,IEDB_145668,IEDB_152206,IEDB_164174,IEDB_167188,IEDB_174332,IEDB_423153,IEDB_76933,IEDB_983930,SB_197,SB_44,SB_67,SB_72

Methods: 1H NMR, GLC-MS, dot immunoblotting, TLC, GLC, anion-exchange chromatography, CC, immunofluorescence analyses, AEC, propidium iodide staining
Comments, role: Сhemical repeating unit frame was shifted in annotation for compatibility with structures elucidated by MS [Eukaryotic Cell 2007, 6: 1464-1473]

Related record ID(s): 43590
NCBI Taxonomy refs (TaxIDs): 178876
Reference(s) to other database(s): GTC:G34376EY
Show glycosyltransferases

There are 8 chemically distinct structures. Please, select:

*O[C@H]1[C@H](O)[C@@H](CO)O[C@H](O[C@@H]2[C@H](O[C@@H]3OC[C@@H](O)[C@H](O)[C@H]3O)[C@@H](O[C@H]3[C@H](O)[C@@H](CO)O[C@H](*)[C@H]3O[C@@H]3OC[C@@H](O)[C@H](O)[C@H]3O)O[C@H](CO)[C@H]2O)[C@H]1O[C@@H]1O[C@H](C(=O)O)[C@@H](O)[C@H](O)[C@H]1O

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Taxonomic group: fungi / Basidiomycota (Phylum: Basidiomycota)
Organ / tissue: capsule
Associated disease: infection due to Cryptococcus neoformans [ICD11: XN3EH

]

NCBI PubMed ID: 19542308
Publication DOI: 10.1128/EC.00013-09
Journal NLM ID: 101130731
Publisher: American Society for Microbiology
Correspondence: de Cock H <h.decock

Cryptococcus neoformans, Glucuronoxylomannan

Structure type: polymer chemical repeating unit ; ~100000
Location inside paper: fig. 1 (GalXM)
Compound class: galactoxylomannan
Contained glycoepitopes: IEDB_114701,IEDB_130701,IEDB_134624,IEDB_136044,IEDB_136906,IEDB_137472,IEDB_141794,IEDB_144983,IEDB_145668,IEDB_151528,IEDB_152206,IEDB_164174,IEDB_167188,IEDB_174332,IEDB_190606,IEDB_983930,SB_163,SB_165,SB_166,SB_187,SB_195,SB_197,SB_44,SB_67,SB_7,SB_72,SB_88

Methods: 1H NMR, GLC-MS, dot immunoblotting, TLC, GLC, anion-exchange chromatography, CC, immunofluorescence analyses, AEC, propidium iodide staining

Related record ID(s): 43589
NCBI Taxonomy refs (TaxIDs): 178876
Reference(s) to other database(s): GTC:G82339HE
Show glycosyltransferases

There are 8 chemically distinct structures. Please, select:

*OC[C@H]1O[C@H](OC[C@H]2O[C@H](OC[C@H]3O[C@H](OC[C@H]4O[C@H](*)[C@H](O)[C@@H](O[C@@H]5O[C@H](CO)[C@H](O[C@H]6O[C@H](CO)[C@@H](O)[C@H](O[C@H]7O[C@H](CO)[C@@H](O)[C@H](O)[C@@H]7O)[C@@H]6O)[C@H](O[C@@H]6OC[C@@H](O)[C@H](O)[C@H]6O)[C@H]5O)[C@H]4O)[C@H](O)[C@@H](O)[C@H]3O)[C@H](O)[C@@H](O[C@@H]3O[C@H](CO)[C@H](O[C@H]4O[C@H](CO)[C@@H](O)[C@H](O[C@H]5O[C@H](CO)[C@@H](O)[C@H](O[C@@H]6OC[C@@H](O)[C@H](O)[C@H]6O)[C@@H]5O)[C@@H]4O[C@@H]4OC[C@@H](O)[C@H](O)[C@H]4O)[C@H](O)[C@H]3O)[C@H]2O)[C@H](O)[C@@H](O)[C@H]1O

SVG MW SMILES 3D mol Ionize