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The interaction between two putative glycosyltransferases is required for glycosylation of a serine-rich streptococcal adhesin.

Bu S, Li Y, Zhou M, Azadin P, Zeng M, Fives-Taylor P, Wu H

Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, Complex Carbohydrate Research Center, University of Georgia at Athens, Athens, GA, Department of Microbiology & Molecular Genetics, University of Vermont, Burlington, VT 05405.

Fap1, a serine-rich glycoprotein, is essential for fimbrial biogenesis and biofilm formation of Streptococcus parasanguis. Fap1-like proteins are conserved in many streptococci and staphylococci and have been implicated in bacterial virulence. Fap1 contains two serine-rich repeat regions that are modified by O-linked glycosylation. A seven-gene cluster has been identified and this cluster is implicated in Fap1 biogenesis. In this study, we investigated the initial step of Fap1 glycosylation by using a recombinant Fap1 as a model. This recombinant molecule has the same monosaccharide composition profile as the native Fap1 protein. Glycosyl linkage analyses indicated that N-acetyl-glucosamine (GlcNAc) is among the first group of sugar residues transferred to the Fap1 peptide. Two putative glycosyltransferases Gtf1 and Gtf2 were essential for the glycosylation of Fap1 with GlcNAc-containing oligosaccharide(s) in both S. parasanguis as well as in the Fap1 glycosylation system in E. coli. Yeast two-hybrid analysis as well as in vitro and in vivo GST pull-down assays demonstrated the putative two glycosyltransferases interacted with each other. The interaction domain was mapped to an N-terminal region of Gtf1 that was required for the Fap1 glycosylation. The data in this study suggested the formation of the Gtf1 and Gtf2 complex was required for the initiation of the Fap1 glycosylation and the N-terminal region of Gtf1 was necessary.

Published 17 December 2007 in J Bacteriol.
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