Structural characteristics of human salivary statherin: a model for boundary lubrication at the enamel surface.

A three-dimensional structural model for salivary statherin in aqueous phase has been developed using structure prediction, circular dichroism, molecular modeling, and mechanics. The relevant structural features of statherin are N-terminal helix segment connected to a long poly-L-proline type II segment, which is followed by a short extended structure. Using this model, the hydroxyapatite binding ability of statherin has been explained. The hydroxyapatite binding region is comprised of the N-terminal acidic residues (Asp-pSer-pSer-Glu-Glu) and Glu-26, which are clustered together in space. Partial conformational unfolding and oriented aggregation of several statherin molecules at the enamel surface provides an amphipathic film that is responsible for the boundary lubrication exhibited by statherin.