Motions of calmodulin characterized using both Bragg and diffuse X-ray scattering

Area of Science:

• Structural biology
• Protein dynamics
• Biophysics

Background:

• Calmodulin is a calcium-activated regulatory protein with a flexible, dumbbell-like structure.
• Understanding calmodulin's motions is crucial for modeling its function.
• It binds to various targets, undergoing conformational changes.

Purpose of the Study:

• To investigate the dynamic motions of calmodulin in a complex with a peptide.
• To characterize large-scale and small-scale motions using X-ray scattering.
• To relate protein dynamics to calmodulin's regulatory function.

Main Methods:

• X-ray crystallography for multiple-conformer refinement.
• Analysis of Bragg reflections to identify anisotropic displacements.
• 3D mapping of large and small scale diffuse X-ray scattering data.

Main Results:

• Anisotropic displacements and high dihedral angle variations observed in flexible linker and calcium-binding sites.
• Liquid-like isotropic motions detected with small correlation length.
• Coupled, anisotropic motions observed along the molecular packing direction.

Conclusions:

• Bragg and diffuse scattering provide a consistent model of calmodulin's flexible linker motions.
• High variations in calcium-binding sites likely affect ion binding affinity, especially in N-terminal sites.
• These dynamics are critical for calmodulin's regulatory role.