title: The WbaK acetyltransferase of Salmonella enterica group E gives insights into O antigen evolution.
abstract: O antigens are polysaccharides consisting of repeat units of three to eight sugars, generally assembled by genes in a discrete O antigen gene cluster. Salmonella enterica produces 46 forms of O antigen, and most of the variation is determined by genes in the gene cluster. However in some cases the structures are modified by enzymes encoded outside of the gene cluster, and several such modifications have been reported for Salmonella enterica group E, some with the genes on bacteriophages and one gene at a distant chromosomal site. We identified the enzyme, WbaK, that is responsible for O-acetylating the subgroup E1 O antigen, and found that the gene is located just downstream of the gene cluster as currently known. The wbaK gene appears to have been imported by a recombination event that also replaced the last 37 bp of the wbaP gene, indicating that homologous recombination was involved. Some of the group E strains we studied must have the original gene cluster, as they lack wbaK and the sequence downstream of wbaP is very similar to that in several other S. enterica O antigen gene clusters. In effect the gene cluster was extended by one gene in subgroup E1. It appears that a function that is usually encoded by a gene outside of the gene cluster has been added to the gene cluster, in this case giving an example of how such gene clusters can evolve.
authors.affiliation: School of Molecular Bioscience, University of Sydney, New South Wales 2006, Australia.
authors.forename: Yaoqin
authors.initials: Y
authors.lastname: Hong
authors.affiliation: Division of Structural Biochemistry, Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Airway Research Center North (ARCN), German Center for Lung Research (DZL), D-23845 Borstel, Germany.
authors.forename: Katarzyna A
authors.initials: KA
authors.lastname: Duda
authors.affiliation: School of Molecular Bioscience, University of Sydney, New South Wales 2006, Australia.
authors.forename: Monica M
authors.initials: MM
authors.lastname: Cunneen
authors.affiliation: Division of Structural Biochemistry, Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Airway Research Center North (ARCN), German Center for Lung Research (DZL), D-23845 Borstel, Germany.
authors.forename: Otto
authors.initials: O
authors.lastname: Holst
authors.affiliation: School of Molecular Bioscience, University of Sydney, New South Wales 2006, Australia.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Reeves
mesh_terms: D000107:Acetylation; D000123:Acetyltransferases / Q000235:genetics* / Q000378:metabolism*; D019143:Evolution, Molecular; D023061:Gene Order; D022761:Gene Transfer, Horizontal; D005810:Multigene Family; D019081:O Antigens / Q000378:metabolism*; D011995:Recombination, Genetic; D019779:Salmonella enterica / Q000201:enzymology* / Q000235:genetics*
chemical_list: D019081:O Antigens; D000123:Acetyltransferases