R. Fujisawa et al., ACIDIC AMINO ACID-RICH SEQUENCES AS BINDING-SITES OF OSTEONECTIN TO HYDROXYAPATITE CRYSTALS, Biochimica et biophysica acta. Protein structure and molecular enzymology, 1292(1), 1996, pp. 53-60
Osteonectin, an acidic noncollagenous protein of bone and dentin, has
affinity to hydroxyapatite crystals. Binding sites to hydroxyapatite o
f this protein were determined by a proteolytic experiment and an in v
itro binding experiment using synthetic peptide analogues. Osteonectin
was adsorbed on hydroxyapatite crystals and digested with trypsin. A
peptide was left adsorbed on the crystal even after the digestion. The
peptide was identified as an amino terminal peptide containing glutam
ic acid-rich sequences, which have been assumed to be possible hydroxy
apatite-binding sites. Poly glutamic acid sequences were synthesized a
s models of the binding sites. Glu(6) peptide was bound to the hydroxy
apatite with a dissociation constant of 2.4 mu M. Peptides containing
fewer glutamic acids had lower affinity to the crystal. Effects of the
se peptides on in vitro mineralization were examined by a gel system i
n microtiter plates. The Glu(6) peptide had a positive effect on the m
ineralization in this system, whereas Asp(6) peptide had a negative ef
fect. These effects indicate the presence of an interaction between th
ese peptides and mineral crystals.