Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 291, Issue 42, Pages 22106-22117Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M116.731695
Keywords
adhesin; crystal structure; glycoprotein biosynthesis; glycosylation; glycosyltransferase; Streptococcus
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Funding
- National Institutes of Health Shared Instrumentation Grant [1S10RR026478]
- Shared Facility Program of the UAB Comprehensive Cancer Center Grant [316851]
- Biotechnology and Biological Sciences Research Council [BB/K016164/1] Funding Source: researchfish
- BBSRC [BB/K016164/1] Funding Source: UKRI
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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- x-ray crystal structure reveals that CgT has a unique binding domain consisting of three 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.
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