Cyclophilin A (CyPA), a cytosolic peptidyl-prolyl trans-cis isomerase can accelerate the trans-cis isomerization of Xxx-Pro peptide bonds. One- and two-dimensional 1H-NMR spectroscopy were used to determine that the heptapeptide Ser-Gln-Asn-Tyr-Pro-Ile-Val, a model peptide of an HIV-1 protease cleavage site in the gag polyprotein of HIV-1, is a substrate for CyPA. Experiments revealed a slow exchange about the Tyr-Pro peptide bond with 30 ± 5% in the cis conformation (pH 1-9). While the interconversion rate is too slow to measure by kinetic NMR methods in the absence of CyPA, these methods, saturation transfer and NOE experiments, established that CyPA enhanced the rate of trans-cis interconversion, a process inhibited by cyclosporin A (CsA). With a substrate:CyPA ratio of 40:1, an interconversion rate of 2.5 s-1 at 25°C was observed.
Bibliographical noteFunding Information:
This work was supported in part by National Institutes of Health grant GM49858. NMR instrumentation was provided with funds from the NSF (BIR-961477) and the University of Minnesota, Medical School.
- Cyclophilin A
- Cyclosporin A
- HIV protease
- Peptidyl-propyl trans-cis isomerase
- gag polyprotein