Interaction of glucosyltransferase with the cell surface of Streptococcus mutans

The partially purified glucosyltransferase (GTF) fraction synthesizing primarily water-insoluble glucans, GTF-A, and the homogeneous fraction synthesizing water-soluble glucans, GTF-B, were utilized to assess the binding of GTF activity to the cell surface of Streptococcus mutans GS-5. Growth of the cells in either Todd-Hewitt broth or a chemically defined medium did not appear to affect the ability of the cells to bind either enzyme fraction. Heat inactivation of the cells did not singificantly reduce the interaction of the enzymes with the cells. Cell surface glucan molecules appear to be involved in GTF binding to the cells because: (i) dextranase or alpha-1,3-glucanase treatment of the cells markedly reduced enzyme binding; (ii) the inclusion of soluble dextrans in the binding assays reduced both GTF-A and GTF-B binding to the cells; and (iii) pretreatment of the cells or the GTF-B fraction with soluble dextrans before binding significantly reduced enzyme binding to the cells. In addition, enzyme binding appears to require a cell surface protein component because Pronase, but not trypsin, treatment of cells reduced enzyme binding. Furthermore, the removal of a portion of the cell surface GTF-glucan complex with 3 N NaCl appears to provide additional binding sites for the enzymes. These results are interpreted in terms of the mechanism of the conversion of extracellular GTF to the cell-associated form.