Analysis of domain interaction in insoluble glucan synthetase of oral streptococci

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 13671904
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Morphological basic dentistry
• Research Institution: Okayama University
• Principal Investigator: FUKUI Kazuhiro OKAYAMA UNIVERSITY, Graduate School of Medicine and Dentistry, Professor, 大学院・医歯学総合研究科, 教授 (70034171)
• Co-Investigator(Kenkyū-buntansha): INOUE Tetsuyoshi OKAYAMA UNIVERSITY, Graduate School of Medicine and Dentistry, Research associate, 大学院・医歯学総合研究科, 助手 (20223258) ; SHINGAKI Ryuji OKAYAMA UNIVERSITY, Graduate School of Medicine and Dentistry, Research associate, 大学院・医歯学総合研究科, 助手 (40294417) ; KOKEGUCHI Susumu OKAYAMA UNIVERSITY, Graduate School of Medicine and Dentistry, Assistant Professor, 大学院・医歯学総合研究科, 助教授 (10144776) ; KODAMA Takao Kyusyu Institute of Technology, Bioinformatics, Professor, 情報工学部, 教授 (30034200)
• Project Period (FY): 2001 – 2003
• Keywords: insoluble glucan synthetase / oral streptococci / domain interaction / dextran-binding domain / GTF-I / Streptococcus sobrinus / catalytic domain

Research Abstract

Insoluble glucan synthetase (GTF) of Streptococcus sobr inus, a member of oral streptococci, is composed of a catalytic domain (GS) in the N-terminal side and a dextran-binding domain (GBD) in the C-terminal side. In this study, we examined the interaction between the two domains, and its effects on the enzymatic activity. GBD consists of six repeat units. We constructed a series of the GTF mutants that have GS with step-wise deleted repeat units (GS-2R 〜 GS-6R) or have an inversion of GS and GBD domains (6R-GS), and used in this study. The results are as follows. 1. GBD was indispensable for binding to dextran. The affinity of GTF for dextran was decreased with decrease of the number of repeat units. 2. Binding of dextran to GBD caused structural change in the enzyme. 3. The GTF mutants with a large deletion in GBD, although having a dextran-binding ability, showed greatly decreased enzymatic activity compared to mutants with a small deletion. 4. In GTF mutatns with a small deletion in GBD, two domains denatured cooperatively, suggesting the interaction of two domains, whereas mutants with a large deletion in GBD, two domains denatured independently. Taken together, the roles of GBD include not only binding to dextran, but also interaction with GS, which enables functional coupling of two domains. This is responsible for dextran-dependent activation of this enzyme.