Abiotrophia defectiva adhere to saliva-coated hydroxyapatite beads via interactions between salivary proline-rich-proteins and bacterial glycerlaldehyde-3-phosphate dehydrogenase

Abiotrophia defectiva is a species of nutritionally variant streptococci that is found in human saliva and dental plaques and that has been associated with infective endocarditis. In our previous study, we found that A. defectiva could bind specifically to saliva-coated hydroxyapatite beads (SHA). In this study, we identified a cell surface component of A. defectiva that promotes adherence to SHA beads. Binding of A. defectiva to SHA was reduced in the presence of antibodies against human proline-rich protein (PRP); these results suggested that PRP may be a critical component mediating the interactions between A. defectiva and the salivary pellicle. Two-dimensional gel electrophoresis of whole A. defectiva cells followed by Far-Western blotting was conducted by probing with synthetic peptides analogous to the binding region of PRP known as PRP-C. The results indicate that an A. defectiva protein of 37 kDa interacts with PRP-C. Results of amino-terminal sequencing of the adhesive A. defectiva protein revealed significant similarity to glycerlaldehyde-3-phosphate dehydrogenase (GAPDH). Recombinant GAPDH bound to immobilized PRP-C in a dose-dependent manner and binding of A. defectiva to SHA or to PRP was reduced in the presence of anti-GAPDH antiserum. Western blotting or electron immunomicroscopic observations with anti-GAPDH antiserum revealed that this protein was expressed in both cytosolic and cell wall fractions. These results suggest that A. defectiva could specifically bind to PRP via interactions with cell surface GAPDH; the findings suggest a mechanism underlying A. defectiva-mediated adherence to saliva-coated tooth surfaces. This article is protected by copyright. All rights reserved.

Keywords: Abiotrophia defectiva; GAPDH; colonization; proline rich proteins; salivary pellicle.