Mechanistic studies of peptidyl prolyl cis-trans isomerase: evidence for catalysis by distortion.
Cyclophilin, the cytosolic binding protein for the immunosuppressive drug cyclosporin A, has recently been shown to be identical with peptidyl prolyl cis-trans isomerase [Fischer, G., Wittmann-Liebold, B., Lang, K., Kiefhaber, T., & Schmid, F.X. (1989) Nature 337, 476; Takahashi, N., Hayano, T., & Suzuki, M. (1989) Nature 337, 473]. To provide a mechanistic framework for studies of the interaction of cyclophilin with cyclosporin, we investigated the mechanism of the PPI-catalyzed cis to trans isomerization of Suc-Ala-Xaa-cis-Pro-Phe-pNA (Xaa = Ala, Gly). Our mechanistic studies of peptidyl prolyl cis-trans isomerase include the determination of steady-state kinetic parameters, pH and temperature dependencies, and solvent and secondary deuterium isotope effects. The results of these experiments support a mechanism involving catalysis by distortion in which the enzyme uses free energy released from favorable, noncovalent interactions with the substrate to stabilize a transition state that is characterized by partial rotation about the C-N amide bond.
Harrison
R K
RK
Department of Enzymology, Merck Research Laboratories, Rahway, New Jersey 07065.
Stein
R L
RL
D000591:Amino Acid Isomerases / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008969:Molecular Sequence Data; D019696:Peptidylprolyl Isomerase; D013379:Substrate Specificity; D013552:Swine; D013816:Thermodynamics; D013950:Thymus Gland / Q000201:enzymology
D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase