Arginine is a Common Ligand for Haemagglutination and Protein Binding by Organisms Inhabiting Mucosal Surfaces

Treponema denticola, T. vincentii and T. socranskii can be added to the diverse group of oral organisms which haemagglutinate via surface receptors that bind proteins and peptides. Model peptides and selective chemical modification of arginyl or lysyl residues of protein ligands showed that for both Porphyromonas gingivalis and oral Treponema , binding involves predominantly arginyl and some lysyl residues. We have previously identified a relationship between protein binding, proteolytic activity and haemagglutination in P. gingivalis and were able to extend this finding to oral Treponema . Oral spirochaetes have both trypsin-and chymotrypsin-like proteases and peptidases and their haemagglutinins are blocked by both trypsin and chymotrypsin inhibitors. The narrow specificity of haemagglutination by these protein-and peptide-binding organisms allows a variety of dissimilar proteins in the oral environment to block haemagglutination. Possession of arginyl-directed haemagglutinins by both the non-motile P. gingivalis and the motile Treponema indicates that adherence to oral surfaces must involve additional mechanisms beyond those demonstrated by in vitro clumping of erythrocytes. The bulky structure and intense charge of the guanidinium group of arginine appear to make this ammo acid residue an 'ideal' ligand in the mucosal environment. Binding of proteins via the guanidinium group of arginine is a widely-occurring adaptation among different species of oral microbes. Agents such as chlorhexidine that also possess guanidinium groups would interfere with the central role of arginine as a ligand involved in a variety of binding reactions exhibited by bacteria inhabiting mucosal surfaces. Keywords: Porphyromonas gingivalis , Treponema denticola, T. vincentii, T. socranskii , haemagglutination, protein binding, arginine, lysine, guanidinium, oral mucosa, adherence.