Hydroxyapatite, (HA, Ca 10(PO 4) 6(OH) 2), is the principal mineral component of bone and teeth, making up approximately 65% by weight of bone and dentin and 95% by weight of dental enamel. There is thus substantial motivation for the development of a more complete understanding of the biomineralization process and of the regulatory roles played by specific proteins. While controlled biomineralization is essential to human life, pathological biomineralization can lead to serious medical conditions such as kidney stones, atherosclerosis, and joint arthropathy. The details remain incompletely understood, but certain proteins are believed to play central roles both in the initial nucleation of biomineral crystals and in the regulation of their subsequent growth, with some proteins acting to inhibit nucleation and growth and others to enhance it –. The process of mineral formation in vivo is complex and involves several stages. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist.īiomineralization is the process by which living organisms produce the minerals that make up hard tissues such as shell, bone, and teeth. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: This research was supported by the Canadian Institutes of Health Research, the Natural Science and Engineering Research Council of Canada, and the Academic Development Fund of the University of Western Ontario. Received: JAccepted: JanuPublished: February 14, 2013Ĭopyright: © 2013 de Bruyn et al. University of Notre Dame, United States of America (2013) Dynamic Light Scattering Study of Inhibition of Nucleation and Growth of Hydroxyapatite Crystals by Osteopontin. This work also demonstrates that dynamic light scattering can be a powerful tool for delineating the mechanism of protein modulation of mineral formation.Ĭitation: de Bruyn JR, Goiko M, Mozaffari M, Bator D, Dauphinee RL, Liao Y, et al. These results suggest that phosphorylations are critical to OPN’s ability to inhibit nucleation, whereas the growth of the hydroxyapatite crystals is effectively controlled by the highly acidic OPN polypeptide. rOPN treated with protein kinase CK2 to phosphorylate the molecule (p-rOPN) produced an effect similar to that of nOPN, but at higher protein concentrations and to a lesser extent. Recombinant osteopontin (rOPN), which lacks phosphorylation, caused no delay in initial calcium phosphate precipitation but severely slowed crystal growth, suggesting that rOPN inhibits growth but not nucleation. Addition of native osteopontin (nOPN) extracted from rat bone caused a delay in the onset of precipitation and reduced the number of particles that formed, but the few particles that did form grew to a larger size than in the absence of the protein. The precipitate was identified as hydroxyapatite by X-ray diffraction. At the ion concentrations studied, immediate precipitation was observed in control experiments with no osteopontin in the solution, and the size of the precipitating particles increased steadily with time. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions.
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