Quaternary diffusion coefficients in a protein-polymer-salt-water system determined by rayleigh interferometry

Area of Science:

• Physical Chemistry
• Biophysics
• Materials Science

Background:

• Understanding multicomponent diffusion is crucial for complex biological and chemical systems.
• Protein diffusion behavior in crowded environments, like cellular cytoplasm, remains an active research area.
• Protein crystallization and enzymology studies often utilize model proteins like lysozyme.

Purpose of the Study:

• To experimentally investigate multicomponent diffusion in a quaternary protein-polymer-salt-water system.
• To measure the nine multicomponent diffusion coefficients for lysozyme-poly(ethylene glycol)-NaCl-water.
• To elucidate the influence of polymer concentration on protein diffusion and salt transport.

Main Methods:

• Precision Rayleigh interferometry was employed to measure diffusion coefficients.
• The study focused on the lysozyme-poly(ethylene glycol)-NaCl-water system at pH 4.5 and 25°C.
• Dynamic light scattering was used to evaluate systematic errors in protein diffusion measurements.

Main Results:

• Protein diffusion coefficient (D(11)) decreased with increasing polymer concentration at low concentrations, aligning with viscosity.
• At high polymer concentrations (250 g/L), protein diffusion was enhanced beyond viscosity predictions.
• Protein concentration gradients induced salt diffusion from high to low protein concentration, amplified by poly(ethylene glycol).

Conclusions:

• Protein diffusion in crowded environments is complex and not solely governed by viscosity.
• The findings provide insights into coupled diffusion phenomena in multicomponent systems.
• This research may inform theoretical models for protein crystallization and diffusion in cellular environments.