title: Control of calcium oxalate crystal growth by face-specific adsorption of an osteopontin phosphopeptide.
abstract: Mineral-associated proteins have been proposed to regulate many aspects of biomineralization, including the location, type, orientation, shape, and texture of crystals. To understand how proteins achieve this exquisite level of control, we are studying the interaction between the phosphoprotein osteopontin (OPN) and the biomineral calcium oxalate monohydrate (COM). In the present study, we have synthesized peptides corresponding to amino acids 220-235 of rat bone OPN (pSHEpSTEQSDAIDpSAEK), one of several highly phosphorylated, aspartic-, and glutamic acid-rich sequences found in the protein. To investigate the role of phosphorylation in interaction with crystals, peptides containing no (P0), one (P1), or all three (P3) phosphates were prepared. Using a novel combination of confocal microscopy and scanning electron microscopy, we show that these peptides adsorb preferentially to {100} faces of COM and inhibit growth of these faces in a phosphorylation-dependent manner. To characterize the mechanism of adsorption of OPN peptides to COM, we have performed the first atomic-scale molecular-dynamics simulation of a protein-crystal interaction. P3 adsorbs to the {100} face much more rapidly than P1, which in turn adsorbs more rapidly than P0. In all cases, aspartic and glutamic acid, not phosphoserine, are the amino acids in closest contact with the crystal surface. These studies have identified a COM face-specific adsorption motif in OPN and delineated separate roles for carboxylate and phosphate groups in inhibition of crystal growth by mineral-associated phosphoproteins. We propose that the formation of close-range, stable, and face-specific interactions is a key factor in the ability of phosphoproteins to regulate biomineralization processes.
authors.affiliation: CIHR Group in Skeletal Development and Remodeling, School of Dentistry, University of Western Ontario, London, Canada.
authors.forename: Bernd
authors.initials: B
authors.lastname: Grohe
authors.forename: Jason
authors.initials: J
authors.lastname: O'Young
authors.forename: D Andrei
authors.initials: DA
authors.lastname: Ionescu
authors.forename: Gilles
authors.initials: G
authors.lastname: Lajoie
authors.forename: Kem A
authors.initials: KA
authors.lastname: Rogers
authors.forename: Mikko
authors.initials: M
authors.lastname: Karttunen
authors.forename: Harvey A
authors.initials: HA
authors.lastname: Goldberg
authors.forename: Graeme K
authors.initials: GK
authors.lastname: Hunter
mesh_terms: D000327:Adsorption; D000595:Amino Acid Sequence; D002129:Calcium Oxalate / Q000737:chemistry*; D003198:Computer Simulation; D003460:Crystallization; D008958:Models, Molecular; D053495:Osteopontin / Q000737:chemistry*; D010748:Phosphopeptides / Q000737:chemistry*
chemical_list: D010748:Phosphopeptides; D053495:Osteopontin; D002129:Calcium Oxalate