title: The salt-dependence of a protein-ligand interaction: ion-protein binding energetics.
abstract: Using the binding of a nucleotide inhibitor (guanosine-3'-monophosphate) to a ribonuclease (ribonuclease Sa) as a model system, we show that the salt-dependence of the interaction arises due to specific ion binding at the site of nucleotide binding. The presence of specific ion-protein binding is concluded from a combination of differential scanning calorimetry and NMR data. Isothermal titration calorimetry data are then fit to determine the energetic profile (enthalpy, entropy, and heat capacity) for both the ion-protein and nucleotide-protein interactions. The results provide insight into the energetics of charge-charge interactions, and have implications for the interpretation of an observed salt-dependence. Further, the presence of specific ion-binding leads to a system behavior as a function of temperature that is drastically different from that predicted from Poisson-Boltzmann calculations.
authors.affiliation: Department of Biochemistry, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Travis T
authors.initials: TT
authors.lastname: Waldron
authors.forename: Greta L
authors.initials: GL
authors.lastname: Schrift
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Murphy
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D002152:Calorimetry, Differential Scanning; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology; D006157:Guanosine Monophosphate / Q000737:chemistry / Q000378:metabolism; D007477:Ions; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008024:Ligands; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012260:Ribonucleases / Q000737:chemistry / Q000378:metabolism; D012492:Salts; D013816:Thermodynamics
chemical_list: D007477:Ions; D007527:Isoenzymes; D008024:Ligands; D011506:Proteins; D011994:Recombinant Proteins; D012492:Salts; C068152:3'-guanylic acid; D006157:Guanosine Monophosphate; D012260:Ribonucleases; C077002:ribonuclease Sa3