Solution structure and internal dynamics of NSCP, a compact calcium-binding protein

Area of Science:

• Structural Biology
• Biochemistry
• Biophysics

Background:

• Sarcoplasmic calcium-binding proteins are crucial for calcium regulation in muscle cells.
• Understanding protein structure-dynamics relationships provides insights into function.

Purpose of the Study:

• To determine the solution structure and internal dynamics of Nereis diversicolor sarcoplasmic calcium-binding protein (NSCP) in its calcium-bound state.
• To correlate structural features with protein flexibility and stability.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy for structure determination using NOE and angular restraints.
• Distance geometry and simulated annealing for structure generation.
• Amide hydrogen/deuterium exchange and 15N nuclear relaxation for internal dynamics analysis.
• Molecular dynamics simulations to analyze backbone generalized order parameter (S2).

Main Results:

• A highly compact and rigid solution structure of NSCP with two closely interacting EF-hand domains was determined.
• Restricted mobility was observed at the protein termini, while Ca2+-binding site II exhibited enhanced flexibility.
• Dynamics analysis revealed a strong correlation between backbone flexibility (S2), exchange rates, and crystallographic B-factors.

Conclusions:

• NSCP adopts a stable, compact structure in the calcium-bound state, with specific regions of flexibility.
• The study provides a detailed understanding of the structure-dynamics interplay in NSCP, relevant for calcium-binding proteins.
• Global unfolding appears to be the mechanism for isotope exchange in most amide protons.