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Conformational studies of osteocalcin in solution
R A Atkinson1, J S Evans, P V Hauschka
1Inorganic Chemistry Laboratory, Oxford, UK.
European Journal of Biochemistry
|September 1, 1995
Summary
Osteocalcin, a calcium-binding protein, exhibits increased alpha-helical structure upon calcium binding, crucial for bone matrix incorporation. Its flexible structure in solution, with exposed gamma-carboxyglutamic acid residues, is essential for protein function.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Osteocalcin is a 49-residue, calcium-binding protein vital for bone matrix formation.
- It contains a disulphide bridge, a proline-rich segment, and three gamma-carboxyglutamic acid (Gla) residues.
- Gla residues are proposed to interact with the bone mineral phase.
Purpose of the Study:
- To investigate the structural changes of osteocalcin upon calcium binding.
- To elucidate the solution structure and flexibility of osteocalcin using NMR and circular dichroism.
Main Methods:
- Circular dichroism (CD) spectroscopy to monitor changes in secondary structure.
- Proton Nuclear Magnetic Resonance (1H-NMR) spectroscopy for resonance assignment and NOE analysis.
- Computational modeling to determine protein conformation based on distance constraints.
Main Results:
- Calcium (Ca2+) binding induces an increase in alpha-helical structure in bovine osteocalcin.
- This induced helical structure is lost upon heating.
- 1H-NMR studies revealed a flexible structure for rabbit osteocalcin in solution, not a single defined conformation.
- Calculated structures show a hydrophobic core and exposed Gla side chains on one face.
Conclusions:
- Calcium binding significantly alters osteocalcin's secondary structure, enhancing its alpha-helicity.
- Osteocalcin possesses a flexible solution structure, potentially key to its biological function in bone.
- The spatial arrangement of Gla residues on one face supports their proposed role in mineral interaction.
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