Interfacial Mineral-Peptide Properties of a Mineral Binding Peptide from Osteonectin and Bone-like Apatite

Osteonectin is a regulator of bone mineralization. It interacts specifically with collagen and apatite through its N-terminal domain, inhibiting crystal growth. In this work, we investigated the interface formed between the mineral and an acidic peptide, ON29, derived from the protein's apatite binding domain. The structural properties of the peptide bound to the mineral and the mineral-peptide interface are characterized using NMR and computational methods. A biomaterial complex is formed by precipitation of the mineral in the presence of the acidic peptide. The peptide gets embedded between mineral particles, which comprise a disordered hydrated coat covering apatite-like crystals. ³¹P SEDRA measurements show that the peptide does not affect the overall proximity between phosphate ions in the mineral. {¹⁵N}¹³C REDOR measurements reveal an α-turn in the center of the free peptide, which is unchanged when it is bound to the mineral. {³¹P}¹³C REDOR and ¹H-¹³C HETCOR measurements show that Glu/Asp carboxylates and Thr/Ala/Val side chains from ON29 are proximate to phosphate and hydroxyl groups in the mineral phases. Predictions of ON29's fold on and off hydroxyapatite crystal faces using ROSETTA-surface are used to model the molecular conformation of the peptide and its apatite-binding interface. The models constructed without bias from experimental results are consistent with NMR measurements and map out extensively the residues forming an interface with apatitic crystals. (Figure Presented).