Solution conformation of a cyclophilin-bound proline isomerase substrate.

Cyclophilin (CyP) is the 17.8-kDa cytosolic receptor of the immunosuppressant cyclosporin A (CsA) and also a peptidyl prolyl cis-trans isomerase (PPIase). In order to gain insights into the PPIase mechanism, transferred nuclear Overhauser effect (TRNOE) measurements by two-dimensional 1H NMR were used to determine the conformation of the isomerase-bound standard model substrate suc-AAPF-pNA. Results indicate a cis-like conformation for the CyP-bound substrate with the A-P peptide bond being no more than 40 degrees out of planarity.