ATTACHMENT OF OSTEOBLASTIC CELLS TO HYDROXYAPATITE CRYSTALS BY A SYNTHETIC PEPTIDE (GLU(7)-PRO-ARG-GLY-ASP-THR) CONTAINING 2 FUNCTIONAL SEQUENCES OF BONE SIALOPROTEIN

We investigated activity of bone sialoprotein (BSP) to mediate attachm ent of cells to hydroxyapatite using a model peptide, Glu(7)-Pro-Arg-G ly-Asp-Thr, which contains a putative hydroxyapatite-binding site (pol y-Glu) and a cell-attachment site. The peptide has affinity to hydroxy apatite with a dissociation constant of 13.5 mu M. The peptide affecte d in vitro mineralization in a gel system, indicating interaction betw een this peptide and calcium phosphate. The osteoblastic cell line MC3 T3-E1 was incubated with hydroxyapatite powder coated with the peptide or proteins. Attachment of the cells was observed on the powder coate d with BSP, but not on the powder coated with serum albumin. The cells were attached to the powder coated with the peptide. The cells were f lattened on the powder, and pseudopods developed. The attachment of th e cells was inhibited by an excessive amount of Gly-Arg-Gly-Asp-Ser pe ptide. In conclusion, BSP mediated attachment of osteoblastic cells to hydroxyapatite, and this activity could be accomplished only by the p oly-Glu sequence and the Arg-Gly-Asp sequence.