title: HIV protease substrate conformation: modulation by cyclophilin A.
abstract: 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 degrees C was observed.
authors.affiliation: Department of Biochemistry, University of Minnesota, Minneapolis 55455-0347, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: McCornack
authors.forename: L T
authors.initials: LT
authors.lastname: Kakalis
authors.forename: C
authors.initials: C
authors.lastname: Caserta
authors.forename: R E
authors.initials: RE
authors.lastname: Handschumacher
authors.forename: I M
authors.initials: IM
authors.lastname: Armitage
mesh_terms: D000591:Amino Acid Isomerases / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002384:Catalysis; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015683:Gene Products, gag / Q000378:metabolism*; D016333:HIV Protease / Q000378:metabolism*; D007536:Isomerism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010446:Peptide Fragments / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase; D011392:Proline / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D015683:Gene Products, gag; D010446:Peptide Fragments; D014443:Tyrosine; D016572:Cyclosporine; D011392:Proline; D016333:HIV Protease; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase