Role of solvent for globular proteins in solution

TL;DR

This paper models how solvent properties influence globular protein solutions, providing an exact phase diagram mapping for attractive square well potentials and simulation results for different interaction models.

Contribution

It introduces a model that incorporates solvent free energy into protein solution phase behavior and offers an exact mapping for square well potentials.

Findings

Existence of upper and lower critical points in phase diagrams.

Closed-loop phase behavior similar to previous studies.

Simulation results for square well and Lennard-Jones models.

Abstract

The properties of the solvent affect the behavior of the solution. We propose a model that accounts for the contribution of the solvent free energy to the free energy of globular proteins in solution. For the case of an attractive square well potential, we obtain an exact mapping of the phase diagram of this model without solvent to the model that includes the solute-solvent contribution. In particular we find for appropriate choices of parameters upper critical points, lower critical points and even closed loops with both upper and lower critical points, similar to one found before [Macromolecules, 36, 5845 (2003)]. In the general case of systems whose interactions are not attractive square wells, this mapping procedure can be a first approximation to understand the phase diagram in the presence of solvent. We also present simulation results for both the square well model and a modified Lennard-Jones model.