Second Virial Coefficient As Determined from Protein Phase Behavior

We quantitatively link the macroscopic phase behavior of protein solutions to protein–protein interactions based on a coarse-grained colloidal approach. We exploit the extended law of corresponding states and apply the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory in order to infer the second virial coefficient b₂, an integral measure of the interaction potential, from the phase behavior, namely, cloud-point temperature (CPT) measurements under conditions favoring protein crystallization. This determination of b₂ yields values that quantitatively agree with the results of static light scattering (SLS) experiments. The strength of the attractions is quantified in terms of an effective Hamaker constant, which accounts for van der Waals attractions as well as non-DLVO forces, such as hydration and hydrophobic interactions. Our approach based on simple lab experiments to determine the CPT in combination with the DLVO theory is expected to facilitate further biophysical research on protein–protein interactions in complex solution environments.