The effects of small, ~102 Da, and larger, >103 Da, cosolutes on the equilibrium stability of monomeric globular proteins are broadly understood: excluded volume stabilizes proteins and chemical interactions are stabilizing when repulsive, but destabilizing when attractive.
Proteins, however, rarely work alone. In an article published in Biochemistry, researchers in the Pielak Group investigate the effects of small and large cosolutes on the equilibrium stability of the simplest defined protein–protein interactions, the side-by-side homodimer formed by the A34F variant of the 56-residue B1 domain of protein G.
The researchers used 19F nuclear magnetic resonance spectroscopy to quantify the effects of urea, trimethylamine oxide, Ficoll, and more physiologically relevant cosolutes on the dimer dissociation constant. The data reveal the same stabilizing and destabilizing influences from chemical interactions as observed in studies of protein stability. Results with more physiologically relevant molecules such as bovine serum albumin, lysozyme, and reconstituted Escherichia coli cytosol reflect the importance of chemical interactions between these cosolutes and the test protein. This study serves as a stepping-stone to a more complete understanding of crowding effects on protein–protein interactions.