Thermodynamic penalty arising from burial of a ligand polar group within a hydrophobic pocket of a protein receptor

J Mol Biol. 2006 Oct 6;362(5):994-1003. doi: 10.1016/j.jmb.2006.07.067. Epub 2006 Aug 1.

Abstract

Here, we examine the thermodynamic penalty arising from burial of a polar group in a hydrophobic pocket that forms part of the binding-site of the major urinary protein (MUP-I). X-ray crystal structures of the complexes of octanol, nonanol and 1,8 octan-diol indicate that these ligands bind with similar orientations in the binding pocket. Each complex is characterised by a bridging water molecule between the hydroxyl group of Tyr120 and the hydroxyl group of each ligand. The additional hydroxyl group of 1,8 octan-diol is thereby forced to reside in a hydrophobic pocket, and isothermal titration calorimetry experiments indicate that this is accompanied by a standard free energy penalty of +21 kJ/mol with respect to octanol and +18 kJ/mol with respect to nonanol. Consideration of the solvation thermodynamics of each ligand enables the "intrinsic" (solute-solute) interaction energy to be determined, which indicates a favourable enthalpic component and an entropic component that is small or zero. These data indicate that the thermodynamic penalty to binding derived from the unfavourable desolvation of 1,8 octan-diol is partially offset by a favourable intrinsic contribution. Quantum chemical calculations suggest that this latter contribution derives from favourable solute-solute dispersion interactions.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Calorimetry
  • Crystallography, X-Ray
  • Hydrophobic and Hydrophilic Interactions
  • Ligands
  • Protein Binding
  • Proteins / chemistry*
  • Proteins / metabolism*
  • Thermodynamics*

Substances

  • Ligands
  • Proteins
  • major urinary proteins