O Acetylation of the Enterobacterial Common Antigen Polysaccharide Is Catalyzed by the Product of the yiaH Gene of Escherichia coli K-12

Abstract

ABSTRACT The carbohydrate component of the enterobacterial common antigen (ECA) of Escherichia coli K-12 occurs primarily as a water-soluble cyclic polysaccharide located in the periplasm (ECA CYC ) and as a phosphoglyceride-linked linear polysaccharide located on the cell surface (ECA PG ). The polysaccharides of both forms are comprised of the amino sugars N -acetyl- d -glucosamine (GlcNAc), N -acetyl- d -mannosaminuronic acid (ManNAcA), and 4-acetamido-4,6-dideoxy- d -galactose (Fuc4NAc). These amino sugars are linked to one another to form trisaccharide repeat units with the structure →3-α- d -Fuc4NAc-(1→4)-β- d -ManNAcA-(1→4)-α- d -GlcNAc-(1→. The hydroxyl group in the 6 position of the GlcNAc residues of both ECA CYC and ECA PG are nonstoichiometrically esterified with acetyl groups. Random transposon insertion mutagenesis of E. coli K-12 resulted in the generation of a mutant defective in the incorporation of O -acetyl groups into both ECA CYC and ECA PG . This defect was found to be due to an insertion of the transposon into the yiaH locus, a putative gene of unknown function located at 80.26 min on the E. coli chromosomal map. Bioinformatic analyses of the predicted yiaH gene product indicate that it is an integral inner membrane protein that is a member of an acyltransferase family of enzymes found in a wide variety of organisms. The results of biochemical and genetic experiments presented here strongly support the conclusion that yiaH encodes the O -acetyltransferase responsible for the incorporation of O -acetyl groups into both ECA CYC and ECA PG . Accordingly, we propose that this gene be designated wecH .