SALIVA PROTEINS AND BACTERIAL ADHESION TO ORAL SURFACES

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The objective of this proposal is to understand the molecular mechanisms involved in initial adhesion of commensal and pathogenic bacteria to tooth surfaces. An understanding of this primary step in colonization can provide a starting point for developing methods to prevent adhesion by pathogens and to enhance colonization by non-pathogenic species, so providing approaches to improving oral health. Adhesion of bacteria to teeth appears to be mediated by macromolecules from saliva, serum and bacteria that adsorb to tooth surfaces to form the acquired enamel pellicle. In the previous period of this grant, several salivary proteins were identified which showed remarkable specificity in their ability to promote adhesion of a number of prominent oral bacteria to dental mineral. The purpose of the aims of the present proposal is to understand these adhesive interactions at the molecular level. Aim I. To determine the molecular basis of the ability of a group of novel human submandibular- sublingual glycoproteins to promote the adhesion of Streptococcus mutans JBP to hydroxyapatite (HA). The composition and oligosaccharide structure of the purified proteins will be determined, and the structural basis of their activity and genetic polymorphism investigated. Their adsorption onto HA and its relationship to adhesion-promoting activity will be quantified. Aim II. To elucidate the molecular features of human salivary acidic proline-rich proteins (PRPs) which underlie their ability to strongly promote the adhesion of Actinomyces viscosus LY7, S. gordonii and certain "mutans" streptococci to HA. The structural features of the Pro- Gin carboxy-terminal dipeptide, which appears to be central to the activity of the PRPs, will be investigated. The differences in the adhesion-promoting activities of the PRP gene products and the smaller PRPs derived by post-translational proteolysis will be studied. The activities of the structurally different Db and Pa PRPs, and a newly isolated polymorphic PRP, will be investigated and compared. These studies will help clarify the significance of the extensive polymorphism of the PRPs, their unusual post-translational cleavages and differences in relative gene expression, related to bacterial adhesion. Aim III. To isolate and characterize additional salivary proteins recently identified as promoters of adhesion of several "mutans" streptococci, S. gordonii and P. gingivalis to HA, and to establish the molecular basis of these as yet uninvestigated adhesive reactions. Aim IV. To isolate and characterize the surface-molecules that mediate adhesion of S. mutans JBP to APPs, and S. gordonii to PRPs, adsorbed onto HA. The pure salivary receptors are available in quantity and will be used to prepare affinity columns for the purification of putative adhesins. Isolated bacterial cell surface molecules will be assessed as adhesins by their interaction with receptors, their acting as adhesion inhibitors, and by determining their location on the bacterial cells or their extensions. The genes coding for the adhesins will be cloned and expressed to provide material for further study, particularly for investigating adhesin-receptor interactions at the molecular level.