Isotope-edited NMR of cyclosporin A bound to cyclophilin: Evidence for a trans 9,10 amide bond.

AUTHORS

Fesik SW , Gampe RT , Holzman TF , Egan DA , Edalji R , Luly JR , Simmer R , Helfrich R , Kishore V , Rich DH . Science. 1990 12 7; 250(4986). 1406-1409

ABSTRACT

The binding of a ¹³C-labeled cyclosporin A (CsA) analog to cyclophilin (peptidyl prolyl isomerase) was examined by means of isotope-edited nuclear magnetic resonance (NMR) techniques. A trans 9,10 peptide bond was adopted when CsA was bound to cyclophilin, in contrast to the cis 9,10 peptide bond found in the crystalline and solution conformations of CsA. Furthermore, nuclear Overhauser effects (NOEs) were observed between the ζ₃ and ε₃ protons of the methylleucine (MeLeu) residue at position 9 of CsA and tryptophan¹²¹ (Trp¹²¹) and phenylalanine (Phe) protons of cyclophilin, suggesting that the MeLeu⁹ residue of CsA interacts with cyclophilin. These results illustrate the power of isotope-edited NMR techniques for rapidly providing useful information about the conformations and active site environment of inhibitors bound to their target enzymes.