Investigation for regulatory mechanisms of GcrR protein for S.mutans gbp Cexpression

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The auther has investigated the regulatory mechanisms of the gcrR gene as a response regulator of two-component regulatory systems for gbpC gene expression. Signal transduction of response regulators is performed by their phosphoryl transfer from their counterparts, sensor-transmitter proteins. The 53rd amino acid aspartate of GcrR protein that is expected as the signal receptor site was changed to aranine by site-directed mutagenesis, and this mutation was introduced into S.mutans chromosome. Albeit this altered GcrR protein in this mutant should not be phosphorylated, this mutant exhibited the same dextran-dependent aggregation phenotype as the wild type strain. Therefore, the authers concluded that GcrR protein does not act as a response regulator but act as a represser. GbpC protein is a member of wall-anchored proteins tethered to peptidoglycan layer. The authers confirmed GbpC expression at cell wall by the Western blot analysis, and the S.mutans cells were indicated to be able t … More o bind to immobilized glucan mediated by the GbpC protein using the BiaCore system. Cell wall anchoring of the protein is mediated by the sortase enzyme. Sortase negative mutant of S.mutans did not exhibit dextran-dependent aggregation phenotype as expected. A nonsense mutation of the gbpC gene was initially found in strain GS-5 and this lead to detection of single nucleotide polymorphisms in the gbpC gene among S.mutans strains. Both conserved and polymorphic regions of the gbpC gene will be useful for an estimation of functional domains of GbpC protein and identification of S.mutans strains. A gbpC gene homologue from Streptococcus macacae was successfully identified by PCR method with primers designed from this conserved GbpC protein information. The authers found another aggregation phenotype designated as cold agglutination. The collagen-binding adhesin gene was identified from some strains of S.mutans by random mutagenesis method using in vitro transposition of Himarl transposon. This is the first report that demonstrates a collagen-binding adhesin from viridans streptococci in human oral indigenous flora. Less