Taxonomic group: bacteria / Proteobacteria
(Phylum: Proteobacteria)
Associated disease: infection due to Campylobacter jejuni [ICD11:
XN4Q5 
]
NCBI PubMed ID: 36093987Publication DOI: 10.1021/acs.biochem.2c00364Journal NLM ID: 0370623Publisher: American Chemical Society
Correspondence: H.M. Holden <hazel_holden
biochem.wisc.edu>; F.M. Raushel <raushel
tamu.edu>
Institutions: Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States, Department of Biochemistry & Biophysics, Texas A&M University, College Station, Texas 77843, United States, Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
Campylobacter jejuni is a human pathogen and one of the leading causes of food poisoning in Europe and the United States. The outside of the bacterium is coated with a capsular polysaccharide that assists in the evasion of the host immune system. Many of the serotyped strains of C. jejuni contain a 6-deoxy-heptose moiety that is biosynthesized from GDP-d-glycero-d-manno-heptose by the successive actions of a 4,6-dehydratase, a C3/C5-epimerase, and a C4-reductase. We identified 18 different C3/C5-epimerases that could be clustered together into three groups at a sequence identity of >89%. Four of the enzymes from the largest cluster (from serotypes HS:3, HS:10, HS:23/36, and HS:41) were shown to only catalyze the epimerization at C3. Three enzymes from the second largest cluster (HS:2, HS:15, and HS:42) were shown to catalyze the epimerization at C3 and C5. Enzymes from the third cluster were not characterized. The three-dimensional structures of the epimerases from serotypes HS:3, HS:23/36, HS:15, and HS:41 were determined to resolutions of 1.5-1.9 A. The overall subunit architecture places these enzymes into the diverse 'cupin' superfamily. Within X-ray coordinate error, the immediate regions surrounding the active sites are identical, suggesting that factors extending farther out may influence product outcome. The X-ray crystal structures are consistent with His-67 and Tyr-134 acting as general acid/base catalysts for the epimerization of C3 and/or C5. Two amino acid changes (A76V/C136L) were enough to convert the C3-epimerase from serotype HS:3 to one that could now catalyze the epimerization at both C3 and C5.
biosynthesis, capsular polysaccharide, Campylobacter jejuni, C3-epimerase, C3/C5-epimerase
Structure type: polymer chemical repeating unit
Location inside paper: scheme 1
Compound class: CPS
Contained glycoepitopes: IEDB_115136,IEDB_137473,IEDB_140630,IEDB_149136
Methods: 1H NMR, X-ray, SDS-PAGE, kinetics assays, genetic methods, biochemical methods, crystallization
3D data: 3D data
NCBI Taxonomy refs (TaxIDs): 197
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There is only one chemically distinct structure:
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