EVIDENCE FOR CONFORMATIONAL CHANGE OF FATTY-ACID-BINDING PROTEIN ACCOMPANYING BINDING OF HYDROPHOBIC LIGANDS

Conformational change of rat liver fatty acid-binding protein was inve stigated by making use of change of protease-susceptibility in the pre sence or absence of bound oleic acid and clofibrate. Delipidated fatty acid-binding protein was rapidly digested by Achromobacter lysyl endo peptidase, bovine alpha-chymotrypsin, and Staphylococcal V8 protease, while protein recombined with oleic acid was strongly refractory to pr oteolysis. This observation indicates that a striking change in the co nformational state of the protein occurred upon lipid binding, and see ms to support the recent hypothesis that the large segment homologous to fatty acid-binding proteins found in a fatty acid-regulated ion cha nnel constitutes a regulatory domain of the channel [Petrou, S., Ordwa y, R.W., Singer, J.J., and Walsh, J.V., Jr. (1993) Trends Biochem. Sci . 18, 41-42]. Clofibrate, which is a potent peroxisome proliferator an d structurally unrelated to oleic acid, also conferred similar proteas e resistance upon the protein. A possible physiological aspect of the present observation is that the cellular level of free fatty acids, wh ich have metabolic importance and cytotoxicity as well, regulates the turnover rate of fatty acid-binding proteins by modulating the proteas e susceptibility of the protein.