Objectives: The S. mutans glucan-binding protein C (GbpC) is a typical Gram-positive wall protein possessing a LPXTG motif, and is involved in dextran-dependent aggregation (ddag), which was observed with cells grown under stress conditions. However, we previously reported that a gbpC::lacZ monitor strain exhibited a low-level expression of the gbpC gene with the cells grown under a non-stress condition where no ddag was observed. Methods: Therefore, we intended to detect GbpC protein and its glucan-binding activity with such cells by employing the Western analysis with anti-GbpC serum and the Biacore biosensor system. Results: Western analysis revealed that a wall-fraction extracted from non-stress cells reacted with anti-GbpC serum at 72 kD, which is a little larger than that calculated from the deduced amino acid sequence of the GbpC protein, while intracellular and concentrated culture supernatant fractions did not exhibit clear positive bands. The Biacore system revealed that S. mutans non-stress cells adhered to the dextran T500-immobilized surface of a biosensor tip, although gbpC- overexpressed cells exhibited the most adherence. Conclusions: These results indicated that S. mutan GbpC protein was expressed in the cells grown under non-stress conditions and that it could act as a lectin-like molecule to mediate the adherence of the cells to a solid surface. This study was supported in part by a Grant-in-Aid from the ministry of Education, Culture, Sports, Science, and Technology (no. 13671952) and supported in part by Oral Health Science Center grant 981A02 from Tokyo Dental College. yusato@tdc.ac.jp.

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