Intrinsic thermodynamics of trifluoromethanesulfonamide and ethoxzolamide binding to human carbonic anhydrase VII

J Mol Recognit. 2015 Mar;28(3):166-72. doi: 10.1002/jmr.2404. Epub 2015 Feb 3.

Abstract

Human carbonic anhydrase (CA) isozyme VII is a cytosolic protein that is highly expressed in the cortex, hippocampus, and thalamus regions within mammalian brain, and expression disorders can cause epilepsy and several cases of malignant brain tumors. Therefore, CA VII is a potential antiepileptic and anticancer drug target. There are numerous sulfonamides that target CAs nonspecifically. It is important to understand the thermodynamics of inhibitor binding and the structural features of the protein-inhibitor complex in order to design specific inhibitors against CA VII. Isothermal titration calorimetry and fluorescent thermal shift assay were used to characterize the intrinsic thermodynamic parameters of trifluoromethanesulfonamide and ethoxzolamide binding to CA VII. Binding experiments were carried out at various pH in different buffers in order to dissect linked protonation of the water molecule bound to the CA VII active site, deprotonation of the sulfonamide group of the inhibitor, and protonation-deprotonation of buffer. Dissection of all those contributions yielded the intrinsic thermodynamic parameters of binding, such as Gibbs free energy, binding enthalpy, entropy, and protein pKa value. Thermal shift assay was also used to determine CA VII stability at various pH.

Keywords: ThermoFluor®; carbonic anhydrase; intrinsic parameters; isothermal titration calorimetry; thermal shift assay.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Calorimetry / methods
  • Carbonic Anhydrase Inhibitors / chemistry*
  • Carbonic Anhydrase Inhibitors / pharmacokinetics
  • Carbonic Anhydrases / metabolism*
  • Ethoxzolamide / chemistry
  • Ethoxzolamide / pharmacokinetics
  • Humans
  • Hydrogen-Ion Concentration
  • Models, Molecular
  • Sulfonamides / chemistry*
  • Sulfonamides / pharmacokinetics*
  • Thermodynamics

Substances

  • Carbonic Anhydrase Inhibitors
  • Sulfonamides
  • Carbonic Anhydrases
  • carbonic anhydrase VI
  • Ethoxzolamide