Equilibrium Clusters in Concentrated Lysozyme Protein Solutions

TL;DR

This study combines simulations and experiments to analyze how lysozyme protein solutions form equilibrium clusters at different concentrations, revealing a transition from monomers to complex clusters as concentration increases.

Contribution

It provides new insights into the formation and structure of equilibrium clusters in concentrated charged protein solutions near physiological conditions.

Findings

At low concentration (<0.012), lysozyme is mostly monomers.

At intermediate concentration (0.033), most proteins form elongated clusters.

At high concentration (0.12), large irregular clusters dominate.

Abstract

We have studied the structure of salt-free lysozyme at 293 K and pH 7.8 using molecular simulations and experimental SAXS effective potentials between proteins at three volume fractions, 0.012, 0.033, and 0.12. We found that the structure of lysozyme near physiological conditions strongly depends on the volume fraction of proteins. The studied lysozyme solutions are dominated by monomers only for <0.012; for the strong dilution 70% of proteins are in a form of monomers. For 0.033 only 20% of proteins do not belong to a cluster. The clusters are mainly elongated. For 0.12 almost no individual particles exits, and branched, irregular clusters of large extent appear. Our simulation study provides new insight into the formation of equilibrium clusters in charged protein solutions near physiological conditions.