McCornack M A, Kakalis L T, Caserta C, Handschumacher R E, Armitage I M
Department of Biochemistry, University of Minnesota, Minneapolis 55455-0347, USA.
FEBS Lett. 1997 Sep 1;414(1):84-8. doi: 10.1016/s0014-5793(97)00974-5.
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.
亲环素A（CyPA）是一种胞质肽基脯氨酰顺反异构酶，可加速Xxx - Pro肽键的反式 - 顺式异构化。利用一维和二维1H - NMR光谱确定七肽Ser - Gln - Asn - Tyr - Pro - Ile - Val（HIV - 1 gag多蛋白中HIV - 1蛋白酶切割位点的模型肽）是CyPA的底物。实验表明，Tyr - Pro肽键的交换缓慢，在顺式构象中占30±5%（pH 1 - 9）。虽然在没有CyPA的情况下，互变速率太慢而无法通过动力学NMR方法测量，但这些方法，即饱和转移和NOE实验，证实CyPA提高了反式 - 顺式互变速率，而该过程受到环孢素A（CsA）的抑制。在底物与CyPA的比例为40:1时，在25℃下观察到互变速率为2.5 s(-1)。
