Multiple forms of dextran-binding proteins from Streptococcus mutans.

We have isolated a series of five proteins which appear to possess characteristic individual capacities for synthesizing dextrans and binding dextrans. Our suggestion that these proteins comprise an isozyme-like distribution of lectin and enzyme activities is, of course, very speculative and remains to be rigourously confirmed. However, the very identification of these several dextran binding proteins provides a biochemical basis to explain numerous observations suggesting that more than one mechanism for dextran binding is possessed by S. mutans (for instance: 24-27), especially the observations with mutants (24). These proteins probably are the molecular determinants of host infection by S. mutans and may prove to be potent immunogens for use in a vaccine. The presence of a dextran-binding lectin in S. mutans implicates this bacterial lectin in the earliest stage of infection: Attachment to host tissues. The multiplicity of proteins possessing characteristic dextran-synthesizing and dextran-binding capacities indicates the complexity of the adherence mechanisms evolved in S. mutans. Experiments with other bacteria (10-12, 28) suggest that bacterial lectins, in concert with host tissue carbohydrates, may be the molecular mediators of host recognition and subsequent initial attachment of bacterial cells to host tissues in non-pathogenic as well as pathogenic bacteria.