title: Characterization of a metal-independent CAZy family 6 glycosyltransferase from Bacteroides ovatus.
abstract: The myriad functions of complex carbohydrates include modulating interactions between bacteria and their eukaryotic hosts. In humans and other vertebrates, variations in the activity of glycosyltransferases of CAZy family 6 generate antigenic variation between individuals and species that facilitates resistance to pathogens. The well characterized vertebrate glycosyltransferases of this family are multidomain membrane proteins with C-terminal catalytic domains. Genes for proteins homologous with their catalytic domains are found in at least nine species of anaerobic commensal bacteria and a cyanophage. Although the bacterial proteins are strikingly similar in sequence to the catalytic domains of their eukaryotic relatives, a metal-binding Asp-X-Asp sequence, present in a wide array of metal ion-dependent glycosyltransferases, is replaced by Asn-X-Asn. We have cloned and expressed one of these proteins from Bacteroides ovatus, a bacterium that is linked to inflammatory bowel disease. Functional characterization shows it to be a metal-independent glycosyltransferase with a 200-fold preference for UDP-GalNAc as substrate relative to UDP-Gal. It efficiently catalyzes the synthesis of oligosaccharides similar to human blood group A and may participate in the synthesis of the bacterial O-antigen. The kinetics for GalNAc transfer to 2'-fucosyl lactose are characteristic of a sequential mechanism, as observed previously for this family. Mutational studies indicate that despite the lack of a metal cofactor, there are pronounced similarities in structure-function relationships between the bacterial and vertebrate family 6 glycosyltransferases. These two groups appear to provide an example of horizontal gene transfer involving vertebrates and prokaryotes.
authors.affiliation: Department of Basic Science, Charles E. Schmidt College of Biomedical Science, Florida Atlantic University, Boca Raton, Florida 33431, USA.
authors.forename: Percy
authors.initials: P
authors.lastname: Tumbale
authors.forename: Keith
authors.initials: K
authors.lastname: Brew
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry; D001439:Bacteroides / Q000201:enzymology*; D001483:Base Sequence; D002241:Carbohydrates / Q000737:chemistry; D002384:Catalysis; D020134:Catalytic Domain; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000378:metabolism; D016695:Glycosyltransferases / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008670:Metals / Q000737:chemistry*; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary
chemical_list: D000942:Antigens, Bacterial; D002241:Carbohydrates; D008670:Metals; D016695:Glycosyltransferases