title: Electrostatic effects on the thermodynamics of protonation of reduced plastocyanin.
abstract: The L12E, L12K, Q88E, and Q88K variants of spinach plastocyanin have been electrochemically investigated. The effects of insertion of net charges near the metal site on the thermodynamics of protonation and detachment from the copper(I) ion of the His87 ligand have been evaluated. The mutation-induced changes in transition enthalpy cannot be explained by electrostatic considerations. The existence of enthalpy/entropy (H/S) compensation within the protein series indicates that solvent-reorganization effects control the differences in transition thermodynamics. Once these compensating contributions are factorized out, the resulting modest differences in transition enthalpies turn out to be those that can be expected on purely electrostatic grounds. Therefore, this work shows that the acid transition in cupredoxins involves a reorganization of the H-bonding network within the hydration sphere of the molecule in the proximity of the metal center that dominates the observed transition thermodynamics and masks the differences that are due to protein-based effects.
authors.affiliation: Department of Chemistry and Centro SCS, University of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy.
authors.forename: Gianantonio
authors.initials: G
authors.lastname: Battistuzzi
authors.forename: Marco
authors.initials: M
authors.lastname: Borsari
authors.forename: Giulia
authors.initials: G
authors.lastname: Di Rocco
authors.forename: Alan
authors.initials: A
authors.lastname: Leonardi
authors.forename: Antonio
authors.initials: A
authors.lastname: Ranieri
authors.forename: Marco
authors.initials: M
authors.lastname: Sola
mesh_terms: D019943:Amino Acid Substitution / Q000502:physiology; D001400:Azurin / Q000737:chemistry; D004563:Electrochemistry; D019277:Entropy; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D010970:Plastocyanin / Q000737:chemistry*; D011522:Protons; D011994:Recombinant Proteins / Q000737:chemistry; D018724:Spinacia oleracea / Q000737:chemistry; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D011522:Protons; D011994:Recombinant Proteins; C050107:cupredoxin; D001400:Azurin; D010970:Plastocyanin