Diffusion and dynamics of γ-globulin in crowded aqueous solutions

Area of Science:

• Biophysics
• Protein dynamics
• Neutron scattering

Background:

• Protein dynamics are crucial for protein function and cellular processes.
• The complex hierarchical nature of protein motion (global diffusion, side-chain, and atomic group movements) presents a significant challenge to full comprehension.
• Understanding these dynamics is vital for advancing fields ranging from drug discovery to cellular biology.

Purpose of the Study:

• To investigate the dynamics of gamma-globulin in solution across various concentrations using quasi-elastic neutron scattering.
• To differentiate between global diffusion (translational and rotational) and internal protein motions.
• To characterize the geometric and dynamic aspects of internal protein motions.

Main Methods:

• Quasi-elastic neutron scattering (QENS) was employed to study gamma-globulin solutions.
• Experiments were conducted over a wide range of volume fractions to observe concentration-dependent effects.
• Data analysis focused on separating global diffusion from internal molecular dynamics.

Main Results:

• Translational and rotational diffusion coefficients were successfully resolved from internal motions.
• Global diffusion of gamma-globulin aligns with effective sphere models, despite its non-spherical shape.
• Internal motions were characterized, indicating methyl group rotations and confined side-chain diffusion.

Conclusions:

• Quasi-elastic neutron scattering provides a powerful tool to dissect complex protein dynamics.
• The study elucidates the distinct contributions of global and internal motions in protein solutions.
• New neutron spectrometer capabilities enable detailed investigations into the coupling between intracellular dynamics and protein function.