Lactobacillus helveticus glycosyltransferases: from genes to carbohydrate synthesis.
Bioactive carbohydrates are crucial in mediating essential biological processes, and their biosynthesis is an essential aspect to develop for a global view of their biological functions. Lactic acid bacteria display an array of diverse and complex carbohydrates and, therefore, are of particular interest. Here we present the identification of a novel exocellular polysaccharide structure and the corresponding gene cluster from Lactobacillus helveticus NCC2745. The development of a glycosyltransferase-specific enzymatic assay allowed the assignment of sugar specificities, which as a general approach will for the future permit a faster and more direct characterization of glycosyltransferase specificities. A model of the biosynthesis of the repeating unit is proposed. EpsE is a phosphoglucosyltransferase initiating the repeating unit biosynthesis by linking a glucose residue to a membrane-associated lipophilic acceptor. EpsF elongates the carbohydrate chain by forming an alpha(1,3)-Glcp linkage onto the first Glcp, whereas EpsG adds a backbone alpha(1,6)-Galp onto alpha-Glcp and EpsH attaches a alpha(1,6)-Glcp branch onto the first glucose residue. Finally, EpsI would add a beta(1,6)-Galp linkage onto alpha-Glcp terminating the sidechain and EpsJ would terminate the synthesis of the polysaccharides' repeating unit by forming a beta(1,3)-Galp linkage onto alpha-Galp.
Jolly
Laure
L
Nestlé Research Center, Vers-chez-les-Blanc, CH-1000 Lausanne 26, Switzerland.
Newell
John
J
Porcelli
Ida
I
Vincent
Sébastien J F
SJ
Stingele
Francesca
F
D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000096:biosynthesis*; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004591:Electrophoresis, Polyacrylamide Gel; D016695:Glycosyltransferases / Q000235:genetics*; D007778:Lactobacillus / Q000201:enzymology* / Q000378:metabolism; D008969:Molecular Sequence Data
D002241:Carbohydrates; D016695:Glycosyltransferases