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Evidence that Water Can Reduce the Kinetic Stability of Protein−Hydrophobic Ligand Interactions

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journal contribution
posted on 22.12.2010, 00:00 by Lan Liu, Klaus Michelsen, Elena N. Kitova, Paul D. Schnier, John S. Klassen
The first quantitative comparison of the thermal dissociation rate constants measured for protein−ligand complexes in their hydrated and dehydrated states is described. Rate constants, measured using surface plasmon resonance spectroscopy, are reported for the dissociation of the 1:1 complexes of bovine β-lactoglobulin (Lg) with the fatty acids (FA), palmitic acid (PA), and stearic acid (SA), in aqueous solution at pH 8 and at temperatures ranging from 5 to 45 °C. The rate constants are compared to values determined from time-resolved blackbody infrared radiative dissociation measurements for the gaseous deprotonated (Lg+FA)n ions, where n = 6 and 7, at temperatures ranging from 25 to 66 °C. Notably, the hydrated (Lg+PA) complex is kinetically less stable than the corresponding gas phase (Lg+PA)n ions at all temperatures investigated; the hydrated (Lg+SA) complex is kinetically less stable than the gaseous (Lg+SA)n ions at temperatures <45 °C. The greater kinetic stability of the gaseous (Lg+FA)n ions originates from significantly larger, by 11−12 kcal mol−1, Ea values. It is proposed that the differences in the dissociation Ea values measured in solution and the gas phase reflect the differential hydration of the reactant and the dissociative transition state.