Attachment of osteoblastic cells to hydroxyapatite crystals by a synthetic peptide (Glu(7)-Pro-Arg-Gly-Asp-Thr) containing two functional sequences of bone sialoprotein

We investigated activity of bone sialoprotein (BSP) to mediate attachment of cells to hydroxyapatite using a model peptide, Glu(7)-Pro-Arg-Gly-Asp-Thr, which contains a putative hydroxyapatite-binding site (poly-Glu) and a cell-attachment site. The peptide has affinity to hydroxyapatite with a dissociation constant of 13.5 mu M. The peptide affected in vitro mineralization in a gel system, indicating interaction between this peptide and calcium phosphate. The osteoblastic cell line MC3T3-E1 was incubated with hydroxyapatite powder coated with the peptide or proteins. Attachment of the cells was observed on the powder coated 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 flattened on the powder, and pseudopods developed. The attachment of the cells was inhibited by an excessive amount of Gly-Arg-Gly-Asp-Ser peptide. In conclusion, BSP mediated attachment of osteoblastic cells to hydroxyapatite, and this activity could be accomplished only by the poly-Glu sequence and the Arg-Gly-Asp sequence.