Crystal structure and hydroxyapatite binding of osteocalcin from porcine

Abstract

<p>Osteocalcin is a bone specific protein produced by osteoblast. The strong association of osteocalcin with bone rendered it a principal biological market for bone metabolism and the most characterized among non-collagenous bone matrix proteins. To gain insight into the function of osteocalcin, the crystal structure of osteocalcin has been determined to 2.0 Å resolution. Contrary to a previous hypothesis that osteocalcin is largely disordered; the crystal structure of osteocalcin is tightly folded. One surface of the structure is relative flat and consists of only negatively charged residues. The arrangements of carboxyl groups on the ϒ-carboxylated glumatic acid residues closely mimic the arrangement of phosphate groups in hydroxyapatite, and they chelate five calcium atoms in the dimer interface with near perfect coordination geometry. When docked to the surface of hydroxyapatite, this surface complimented near perfectly the prism face of hydroxyapatite. The excellent complimentary clearly indicates that osteocalcin can bind to hydroxyapatite with high specificity, it seems reasonable that the presence of bound protein will inhibit further crystal growth on this surface.</p>