Guanylate Kinase Structure and Osmolyte Exclusion Studied by Neutron Scattering and Osmotic Stress

Christopher Stanley, NCNR, NIST and NICHD, National Institutes of health

Protein conformational changes induced by ligand binding are inevitably accompanied by a change in the number of water molecules sequestered in pockets, cavities, and grooves. The significance of hydration to protein-ligand interactions has been illustrated using the osmotic stress technique. We are using small-angle neutron scattering (SANS) coupled with osmotic stress to directly probe the connection between protein structural change, osmolyte exclusion, and thermodynamics for guanylate kinase. We chose this enzyme because it is known to undergo large conformational changes upon binding the ligands GMP and ATP. These changes can be followed in solution with SANS to measure corresponding changes in the protein shape and radius of gyration. To compare with these structural results, we measure the thermodynamics of ligand binding by isothermal titration calorimetry and osmotic stress. The application of osmotic stress can lead to new insights into the mechanics of protein conformational changes and more generally, the relationship among protein structure, flexibility, energetics, and function.

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