HIV PROTEASE SUBSTRATE CONFORMATION - MODULATION BY CYCLOPHILIN-A

Cyclophilin A (CyPA), a cytosolic peptidyl-prolyl trans-cis isomerase can accelerate the trans-cis isomerization of Xxx-Pro peptide bonds. O ne- and two-dimensional H-1-NMR spectroscopy were used to determine th at the heptapeptide Ser-Gln-Asn-T yr-Pro-Ile-Val, a model peptide of a n HIV-1 protease cleavage site in the gag polyprotein of HIV-1, if a s ubstrate 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 bu kinetic NMR methods in the absence of CyPA, these methods, saturation transfer and NOE ex periments, established that CyPA enhanced the rate of trans-cif interc onversion, a process inhibited by cyclosporin A (CsA), With a substrat e:CyPA ratio of 40:1, an interconversion rate of 2.5 s(-1) at 25 degre es C was observed. (C) 1997 Federation of European Biochemical Societi es.