A simple patchy colloid model for the phase behavior of lysozyme dispersions

Area of Science:

• Protein thermodynamics
• Soft matter physics
• Biophysical chemistry

Background:

• Understanding protein phase behavior is crucial for controlling protein crystallization and formulation.
• Lysozyme exhibits complex phase diagrams influenced by inter-protein interactions.
• Accurate theoretical models are needed to predict and interpret experimental observations.

Purpose of the Study:

• To develop a minimal theoretical model for spherical proteins with anisotropic interactions.
• To describe the equilibrium phase behavior of lysozyme, including solubility and gas-liquid coexistence.
• To validate the model against experimental data and investigate the role of salt concentration.

Main Methods:

• A minimal model for spherical proteins with aeolotopic pair interactions was proposed.
• Repulsive screened Coulomb interactions and attractive surface patches (Yukawa potential) were incorporated.
• Helmholtz free energy was calculated using second-order thermodynamic perturbation theory.
• Model parameters were fitted to experimental gas-liquid critical point data.

Main Results:

• The model successfully predicted the solubility curve of lysozyme, showing fair agreement with experimental data.
• New experimental data for gas-liquid coexistence curves at various salt concentrations were presented.
• Model calculations for gas-liquid coexistence were compared with new experimental data.
• The strength and range of attractive interactions were found to be weakly dependent on salt concentration.

Conclusions:

• The minimal model provides a good description of lysozyme's equilibrium phase behavior.
• The model highlights the importance of anisotropic attractive interactions in protein self-assembly.
• The weak dependence of attractive forces on salt concentration offers insights into protein solution behavior.