Protein–solvent and weak protein–protein interactions in halophilic malate dehydrogenase

Abstract

With the aim to correlate the solvation, stability and solubility properties of halophilic malate dehydrogenase, we characterized its weak interparticle interactions by small-angle neutron scattering in various solvents. The protein concentration dependence of the apparent radius of gyration and forward scattered intensity extrapolated from Guinier plots, and thus the second virial coefficient, A 2, were determined for each solvent condition. In NaCl 1M+2-methylpentane-2,4-diol 30%, a solvent that promotes protein crystallization, A 2 is negative, −0.4×10 −4 ml mol g −2 and indicating attractive interactions; in ammonium sulfate 3M, in which the protein precipitates at high concentrations, A 2∼0. In 2–5M NaCl, 1–3.5M NaOAc, 1–4.5M KF or 1–2M (NH 4) 2SO 4, in which the protein is very soluble, A 2 is positive with a value of the order of 0.4×10 −4 ml mol g −2 which decreases with increasing salt concentration. In MgCl 2 however, A 2 increases with increasing salt concentration from 0.2 to 1.3M.