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Coarse-Grained Strategy for Modeling Protein Stability in Concentrated Solutions

Jason K. Cheung ^* and Thomas M. Truskett ^* 

^* Department of Chemical Engineering, and Institute of Theoretical Chemistry, The University of Texas at Austin, Austin, Texas

Correspondence: Address reprint requests to Thomas M. Truskett, Dept. of Chemical Engineering, The University of Texas at Austin C0800, Austin, TX 78712. Tel.: 512-471-6308; Fax: 512-471-7060; E-mail: truskett{at}che.utexas.edu.

We present a coarse-grained approach for modeling the thermodynamic stability of single-domain globular proteins in concentrated aqueous solutions. Our treatment derives effective protein-protein interactions from basic structural and energetic characteristics of the native and denatured states. These characteristics, along with the intrinsic (i.e., infinite dilution) thermodynamics of folding, are calculated from elementary sequence information using a heteropolymer collapse theory. We integrate this information into Reactive Canonical Monte Carlo simulations to investigate the connections between protein sequence hydrophobicity, protein-protein interactions, protein concentration, and the thermodynamic stability of the native state. The model predicts that sequence hydrophobicity can affect how protein concentration impacts native-state stability in solution. In particular, low hydrophobicity proteins are primarily stabilized by increases in protein concentration, whereas high hydrophobicity proteins exhibit richer nonmonotonic behavior. These trends appear qualitatively consistent with the available experimental data. Although factors such as pH, salt concentration, and protein charge are also important for protein stability, our analysis suggests that some of the nontrivial experimental trends may be driven by a competition between destabilizing hydrophobic protein-protein attractions and entropic crowding effects.

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