Folding of the C-terminal bacterial binding domain in statherin upon adsorption onto hydroxyapatite crystals.

Statherin is an enamel pellicle protein that inhibits hydroxyapatite (HAP) nucleation and growth, lubricates the enamel surface, and is recognized by oral bacteria in periodontal diseases. We report here from solid-state NMR measurements that the protein's C-terminal region folds into an alpha-helix upon adsorption to HAP crystals. This region contains the binding sites for bacterial fimbriae that mediate bacterial cell adhesion to the surface of the tooth. The helical segment is shown through long-range distance measurements to fold back onto the intermediate region (residues Y16-P28) defining the global fold of the protein. Statherin, previously shown to be unstructured in solution, undergoes conformation selection on its substrate mineral surface. This surface-induced folding of statherin can be related to its functionality in inhibiting HAP crystal growth and can explain how oral pathogens selectively recognize HAP-bound statherin.