ARGININE IS A COMMON LIGAND FOR HEMAGGLUTINATION AND PROTEIN-BINDING BY ORGANISMS INHABITING MUCOSAL SURFACES

Treponema denticola, T. vincentii and T. socranskii can be added to th e diverse group of oral organisms which haemagglutinate via surface re ceptors that bind proteins and peptides. Model peptides and selective chemical modification of arginyl or lysyl residues of protein ligands showed that for both Polphyromonas gingivalis and oral Treponema, bind ing involves predominantly arginyl and some lysyl residues. We have pr eviously identified a relationship between protein binding, proteolyti c activity and haemagglutination in P. gingivalis and were able to ext end this finding to oral Treponema. Oral spirochaetes have both trypsi n- and chymotrypsin-like proteases and peptidases and their haemagglut inins are blocked by both trypsin and chymotrypsin inhibitors. The nar row specificity of haemagglutination by these protein- and peptide-bin ding organisms allows a variety of dissimilar proteins in the oral env ironment to block haemagglutination. Possession of arginyl-directed ha emagglutinins by both the non-motile P. gingivalis and the motile Trep onema indicates that adherence to oral surfaces must involve additiona l mechanisms beyond those demonstrated by in vitro clumping of erythro cytes. The bulky structure and intense charge of the guanidinium group of arginine appear to make this amino acid residue an 'ideal' ligand in the mucosal environment. Binding of proteins via the guanidinium gr oup of arginine is a widely-occurring adaptation among different speci es of oral microbes. Agents such as chlorhexidine that also possess gu anidinium groups would interfere with the central role of arginine as a ligand involved in a variety of binding reactions exhibited by bacte ria inhabiting mucosal surfaces.