title: New Helical Binding Domain Mediates a Glycosyltransferase Activity of a Bifunctional Protein.
abstract: Serine-rich repeat glycoproteins (SRRPs) conserved in streptococci and staphylococci are important for bacterial colonization and pathogenesis. Fap1, a well studied SRRP is a major surface constituent of Streptococcus parasanguinis and is required for bacterial adhesion and biofilm formation. Biogenesis of Fap1 is a multistep process that involves both glycosylation and secretion. A series of glycosyltransferases catalyze sequential glycosylation of Fap1. We have identified a unique hybrid protein dGT1 (dual glycosyltransferase 1) that contains two distinct domains. N-terminal DUF1792 is a novel GT-D-type glycosyltransferase, transferring Glc residues to Glc-GlcNAc-modified Fap1. C-terminal dGT1 (CgT) is predicted to possess a typical GT-A-type glycosyltransferase, however, the activity remains unknown. In this study, we determine that CgT is a distinct glycosyltransferase, transferring GlcNAc residues to Glc-Glc-GlcNAc-modified Fap1. A 2.4-Å x-ray crystal structure reveals that CgT has a unique binding domain consisting of three α helices in addition to a typical GT-A-type glycosyltransferase domain. The helical domain is crucial for the oligomerization of CgT. Structural and biochemical studies revealed that the helix domain is required for the protein-protein interaction and crucial for the glycosyltransferase activity of CgT in vitro and in vivo As the helix domain presents a novel structural fold, we conclude that CgT represents a new member of GT-A-type glycosyltransferases.
authors.affiliation: From the Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and.
authors.forename: Hua
authors.initials: H
authors.lastname: Zhang
authors.affiliation: From the Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and.
authors.forename: Meixian
authors.initials: M
authors.lastname: Zhou
authors.affiliation: the Department of Life Sciences, Imperial College London, London, SW7 2AZ, United Kingdom.
authors.forename: Tiandi
authors.initials: T
authors.lastname: Yang
authors.affiliation: the Department of Life Sciences, Imperial College London, London, SW7 2AZ, United Kingdom.
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Haslam
authors.affiliation: the Department of Life Sciences, Imperial College London, London, SW7 2AZ, United Kingdom.
authors.forename: Anne
authors.initials: A
authors.lastname: Dell
authors.affiliation: From the Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and hwu@uab.edu.
authors.forename: Hui
authors.initials: H
authors.lastname: Wu
mesh_terms: D020816:Amino Acid Motifs; D018360:Crystallography, X-Ray; D036781:Fimbriae Proteins / Q000737:chemistry* / Q000235:genetics; D016695:Glycosyltransferases / Q000737:chemistry* / Q000235:genetics; D000072417:Protein Domains; D013291:Streptococcus / Q000201:enzymology* / Q000235:genetics
chemical_list: C403708:fap1 protein, Streptococcus; D036781:Fimbriae Proteins; D016695:Glycosyltransferases
keywords: Streptococcus; adhesin; crystal structure; glycoprotein biosynthesis; glycosylation; glycosyltransferase