Phosphorylation regulates the secondary structure and function of dentin phosphoprotein peptides

Area of Science:

• Biochemistry
• Biomaterials Science
• Structural Biology

Background:

• Dentin phosphoprotein (DPP) is a key acidic protein in vertebrate dentin and bone formation.
• Its precise role in biomineralization, particularly its interaction with hydroxyapatite (HA), remains largely unknown.
• DPP is structurally classified as an intrinsically disordered protein.

Purpose of the Study:

• To investigate the structural and functional roles of DPP in hydroxyapatite (HA) formation.
• To elucidate how phosphorylation influences DPP's interaction with HA.
• To understand the mechanisms underlying DPP's control over biomineralization.

Main Methods:

• Atomistic molecular dynamics simulations to screen DPP binding domains onto HA.
• Selection and experimental characterization of a DPP-derived peptide (P5) and its phosphorylated form (P5P).
• Small-angle X-ray scattering (SAXS), circular dichroism (CD), and Fourier-transform infrared spectroscopy (FTIR) were used to analyze protein structure.

Main Results:

• DPP peptide P5 was disordered in solution, while its phosphorylated form (P5P) adopted more compact conformations.
• P5 exhibited a random coil structure, whereas P5P formed β-sheet and α-helix structures upon binding to HA.
• P5 inhibited HA crystal growth, while P5P stimulated it, demonstrating phosphorylation-dependent functional changes.

Conclusions:

• Phosphorylation induces structural changes in DPP, transitioning it from a disordered to a more ordered state.
• These structural changes directly regulate DPP's interaction with HA, controlling its effects on crystal growth.
• DPP's phosphorylation-dependent structural modulation is crucial for regulating HA formation in dentin and bone.