Calcium Mineral-Peptide Interactions

Abstract

AbstractPeptides have been synthesized by solid phase methods with structures which are in part based on experimentally-determined features of a major class of organic matrix phosphoproteins isolated from the calcium carbonate shell of the oyster. The matrix structures mimicked in the synthetic peptides included runs of aspartic acid (Asp), which were contrasted with peptides having other deployments of Asp with serine (Ser) and glycine (Gly). In addition, peptide-Ser was phosphorylated (PSer) and the hydrophobic carboxyterminus of natural matrix was mimicked using polyalanine tails. The interaction of the various peptides with CaCO3as well as calcium phosphates was determined using a variety of crystallization assays and studies of adsorption of radio-labelled peptides to crystal surfaces.In general, peptides that include runs of Asp regulate crystal nucleation and growth more effectively than those which contain (Asp-X)nor (Asp-X-Y)nsequences with X and Y being either Gly or Ser. Further, CaCO3crystals have a much higher binding capacity for polyAsp than for peptides with other deployments of Asp. Phosphorylation increases the regulatory activity and the crystal capacities of Asp/Ser - containing peptides. PolyAsp peptides having terminal PSer's are especially effective as regulators of CaCO3nucleation and the conversion of amorphous calcium phosphate to apatite. The activity of Asp15molecules in CaCO3nucleation assays is markedly increased by the addition of polyalanine tails.