Dept of Molecular Biology and Biotechnology, University of Sheffield – m.williamson@sheffield.ac.uk

Taming protein interactions

All proteins have evolved to interact, and in most cases this interaction is with other proteins. Sometimes the interactions are strong, but more often they are weak (Kd > 10 μM), especially in the crowded environment of the cell. Such interactions are hard to detect by many techniques, though usually straightforward by NMR. Weak interactions are characterised by entropy/enthalpy compensation, and in particular by the importance of solvating water. This importance is illustrated by the pervasiveness of the Hofmeister series, which originates from surface tension of the solvent layer around a protein. The effect of osmolytes on proteins can be considered in the same way. Protein interactions and solubility are therefore dependent on the strength of the interaction of the protein with solvent. In working with concentrated protein solutions, the aim is not to remove protein interactions, but to tailor the surface layer to produce tamable interactions.

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