Binding of a Streptococcus mutans cationic protein to kidney in vitro

An 8-kDa protein, with binding activity for heparin and heparan sulfate of basal laminae of animal tissues, was isolated from Streptococcus mutans MT703 and purified to homogeneity. Binding of radioiodinated 8-kDa protein to rabbit kidney tissue in vitro showed a high degree of specificity, as indicated by saturation kinetics, time dependence, and competitive inhibition by unlabeled protein. Binding activity for kidney tissue was competitively inhibited by selected glycosaminoglycans and polyanions in the following order: heparin greater than dextran sulfate greater than heparan sulfate greater than chondroitin sulfate greater than lipoteichoic acid greater than keratan sulfate greater than hyaluronic acid. Binding of the streptococcal protein to rabbit kidney tissue was also strongly inhibited by protamine sulfate, polylysine, and a random copolymer of lysine and alanine. Among the monosaccharides tested at 50 mM, glucosamine 2,3- or 2,6-disulfate, glucuronic acid, glucose 6-phosphate, and glucose 6-sulfate inhibited 50% or more of the binding activity, whereas N-acetylglucosamine 3-sulfate, glucosamine 6-sulfate, N-acetyl-glucosamine, N-acetylgalactosamine, N-acetylneuraminic acid, and a selection of neutral sugars were not inhibitory. The heparin-binding protein was detected on the cell wall of S. mutans and in the culture medium following growth. Several other species of streptococci produce an immunologically related protein of similar size.