High-resolution structure of calcium-loaded calbindin D9k

Area of Science:

• Structural Biology
• Biochemistry
• Molecular Biophysics

Background:

• Calbindin D9k is a calcium-binding protein crucial for cellular calcium homeostasis.
• Understanding its three-dimensional structure is key to elucidating its function in calcium buffering and transport.

Purpose of the Study:

• To determine the solution structure of calcium-loaded calbindin D9k using nuclear magnetic resonance (NMR) spectroscopy.
• To compare the solution structure with the existing crystal structure and identify any discrepancies.

Main Methods:

• Nuclear magnetic resonance (NMR) spectroscopy was employed to collect experimental constraints.
• Distance geometry and restrained molecular dynamics calculations were used to generate and refine the 3D structure.
• Stereospecific assignments were made for prochiral methylene protons and methyl groups of valine and leucine residues.

Main Results:

• A high number of distance (1002) and dihedral angle (174) constraints were utilized for structure refinement.
• The refined solution structure exhibits a core of four antiparallel helices forming two EF-hand calcium-binding motifs.
• The average solution structure closely resembles the crystal structure, with minor deviations attributed to crystal contacts or solution dynamics.

Conclusions:

• The solution structure of calcium-loaded calbindin D9k is well-defined, featuring characteristic EF-hand motifs.
• The structural similarity between solution and crystal forms suggests conserved structural features, with observed differences explained by environmental factors.
• This study provides valuable insights into the dynamic and structural properties of calbindin D9k in solution.