Analysis of domain interaction in insoluble glucan synthetase of oral streptococci

点击翻译按钮获取中文摘要

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.