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J. Biol. Chem., Vol. 283, Issue 7, 3827-3838, February 15, 2008
Analysis and Molecular Modeling of the Formation, Structure, and Activity of the Phosphatidylserine-Calcium-Phosphate Complex Associated with Biomineralization*From the Department of Chemistry and Biochemistry, Graduate Science Research Center, University of South Carolina, Columbia, South Carolina 29208
The nucleational core of matrix vesicles contains a complex (CPLX) of phosphatidylserine (PS), Ca2+, and inorganic phosphate (Pi) that is important to both normal and pathological calcification. Factors required for PS-CPLX formation and nucleational activity were studied using in vitro model systems and molecular dynamic simulations. Ca2+ levels required for and rates of PS-CPLX formation were monitored by light scattering at 340 nm, assessing changes in amount and particle size. Fourier transform infrared spectroscopy was used to explore changes in chemical structure and composition. Washing with pH 5 buffer was used to examine the role of amorphous calcium phosphate in CPLX nucleational activity, which was assessed by incubation in synthetic cartilage lymph with varied pH values. Addition of 4 Ca2+/PS was minimally required to form viable complexes. During the critical first 10-min reaction period, rapid reduction in particle size signaled changes in PS-CPLX structure. Fourier transform infrared spectroscopy revealed increasing mineral phosphate that became progressively deprotonated to
Received for publication, September 12, 2007 , and in revised form, December 7, 2007. * This work was supported by National Institutes of Health NIAMS Grants AR42359 (to L.. N. Y. W.) and AR18983 (to R. E. W.) and Department of Defense, Office of Naval Research Grant N00014-97-1-0806 (to B. R. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 To whom correspondence should be addressed: Dept. of Chemistry and Biochemistry, University of South Carolina, 631 Sumter St., Graduate Science Research Center, Columbia, SC 29208. Tel.: 803-777-6626; Fax: 803-777-9521; E-mail: wuthier{at}mail.chem.sc.edu.
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