The low-density/high-density liquid phase transition for model globular proteins

TL;DR

This study investigates how molecule size and interaction range influence phase transitions, surface tension, and nucleation in model globular proteins using simulations and density functional theory, revealing dominant effects of excluded volume.

Contribution

It introduces a parametrized potential bridging simple fluids and protein interactions, highlighting the impact of excluded volume on phase behavior and nucleation properties.

Findings

Large excluded volume dominates surface tension and nucleation.

Range of interaction affects simple fluids more than proteins.

Nucleation barriers are low, leading to high nucleation rates.

Abstract

The effect of molecule size (excluded volume) and the range of interaction on the surface tension, phase diagram and nucleation properties of a model globular protein is investigated using a combinations of Monte Carlo simulations and finite temperature classical Density Functional Theory calculations. We use a parametrized potential that can vary smoothly from the standard Lennard-Jones interaction characteristic of simple fluids, to the ten Wolde-Frenkel model for the effective interaction of globular proteins in solution. We find that the large excluded volume characteristic of large macromolecules such as proteins is the dominant effect in determining the liquid-vapor surface tension and nucleation properties. The variation of the range of the potential only appears important in the case of small excluded volumes such as for simple fluids. The DFT calculations are then used to study homogeneous nucleation of the high-density phase from the low-density phase including the nucleation barriers, nucleation pathways and the rate. It is found that the nucleation barriers are typically only a few $k_{B}T$ and that the nucleation rates substantially higher than would be predicted by Classical Nucleation Theory.