December 14, 2006
The enamel pellicle is the thin biofilm that forms on our teeth shortly after brushing. As dentists note, that’s not a bad thing because the pellicle, an amalgam of salivary proteins and glycoproteins, adhere to the enamel’s mineralized hydroxyapatite crystals and perform a number vital housekeeping functions, such as inhibiting crystal growth, serving as a barrier to acids, and allowing remineralization. However, the pellicle is a dynamic structure that also serves as the foundation upon which oral bacteria colonize the tooth surface and grow into a complex and potentially disease-causing biofilm.
What’s been especially difficult to determine for a variety of technical reasons is the three-dimensional structure of proteins in the pellicle as they adsorb - or, condense tightly within a thin layer - to the enamel. Solving this structural puzzle will help in variety of areas, from fighting tooth decay and periodontal disease to engineering and maintaining replacement tooth enamel. In the October 31 issue of the Proceedings of the National Academy of Sciences, NIDCR grantees provide an important structural determination of the pellicle protein statherin, which mediates bacterial adhesion to the tooth surface. Using solid-state nuclear magnetic resonance, the authors report the first direct, high-resolution 3D determination of the loop-like folding pattern of statherin’s C terminal as it actually binds on hydroxyapatite. The C terminal receptor domain is of particular interest because it seems to be where the finger-like fimbriae of oral bacteria touch down and bind. Interestingly, the authors confirmed that the C terminal is unstructured in solution. This may explain why fimbriae don’t bind to statherin in saliva but only after the protein has adsorbed and folded the C terminal on tooth enamel.