Association of protein with the cell wall of Streptococcus mutans

Abstract

Cell walls from S. mutans were prepared by conventional techniques and subjected to a series of extraction procedures involving classical protein solvents. The extracted walls contained several non-peptidoglycan amino acids and were amenable to radiolabeling with [125I]NaI and chloramine T. The cell walls could be chemically modified with tetranitromethane and diazo-1H-tetrazole, suggesting the presence of tyrosine, histidine or both. Fluorescence spectra of the walls revealed the presence of tyrosine or tryptophan. Several proteases including pronase, trypsin, subtilisin and proteinase K removed some of the label from the walls. Treatment of the walls with salts or denaturants did not result in solubilization of label. When the walls were solubilized with mutanolysin and subjected to chromatography, 3 peaks of radioactivity with apparent MW of 73,000, 39,000 and 9600 were observed. Wall digests subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single band of radioactivity corresponding to an apparent MW of 79,000. Isoelectric focusing of labeled wall digests gave rise to 2 major bands or radioactivity with isoelectric points of approximately 2.4 and 5.6. The cell wall of S. mutans may contain tightly and possibly covalently bound polypeptide molecules. The cell wall polypeptides of S. mutans may serve as factors in attachment of the bacteria to smooth surfaces. [This may be relevant to the pathogenesis of dental caries].