How does osteocalcin lacking γ-glutamic groups affect biomimetic apatite formation and what can we say about its structure in mineral-bound form?

Abstract

Non-collagenous proteins such as osteocalcin function as regulators of the mineralization process in bone. Osteocalcin undergoes post-translational modification adding an extra carboxylate group on three of its glutamate residues to enhance interaction with bone mineral. In this work, we examine regulation of biomimetic apatite formation by osteocalcin that was not modified after translation. We analyze the structural features in the protein and mineral-protein interfaces to elicit the unmodified protein's fold inside the mineral and to unveil the species that interact with the mineral surface. The results presented here give clues on the protein's active role in controlling the mineral phases that are formed on hydroxyapatite crystals and its ability to influence the extent of order in these crystals.

Keywords: Apatite regulation; Biomineralization; Mineral bound protein; Non-collagenous proteins; Protein conformation; Protein-mineral interface; Solid state NMR.