MUTANTS OF RAT INTESTINAL FATTY-ACID-BINDING PROTEIN ILLUSTRATE THE CRITICAL ROLE PLAYED BY ENTHALPY-ENTROPY COMPENSATION IN LIGAND-BINDING

Site-specific variants of rat intestinal fatty acid-binding protein we re constructed to identify the molecular interactions that are importa nt for binding to fatty acids (FAs). Several variants displayed affini ties that appeared incompatible with the crystal structure of the prot ein-FA complex. Thermodynamic measurements provided an explanation for these apparent inconsistencies and revealed that binding affinities o ften inaccurately reported changes in protein-FA interactions because changes in the binding entropy and enthalpy were usually compensatory. These results demonstrate that understanding the effects of amino aci d replacements on ligand binding requires measurements of enthalpy and entropy, in addition to affinity.