Schmid F X, Grafl R, Wrba A, Beintema J J
Proc Natl Acad Sci U S A. 1986 Feb;83(4):872-6. doi: 10.1073/pnas.83.4.872.
The isomerization of the proline peptide bond between tyrosine-92 and proline-93 in bovine pancreatic ribonuclease A has been investigated in the unfolded protein as well as during the slow refolding process. This bond is in the cis state in the native protein. By comparison of various homologous ribonucleases we show that isomerization of proline-93 is associated with a change in fluorescence of tyrosine-92. This provides a spectroscopic probe to monitor this process in the disordered chain after unfolding as well as its reversal in the course of slow refolding. In unfolded ribonuclease incorrect trans isomers of proline-93 are found in both slow-folding species. trans----cis reversal of isomerization of this proline peptide bond during refolding shows kinetics that are identical with the time course of formation of native protein. Isomerization of proline-93 is slower than the formation of a native-like folded intermediate that accumulates on the major slow refolding pathway. Models to explain these results are discussed.
我们研究了牛胰核糖核酸酶A中酪氨酸92和脯氨酸93之间脯氨酸肽键在未折叠蛋白以及缓慢重折叠过程中的异构化。该肽键在天然蛋白中处于顺式状态。通过比较各种同源核糖核酸酶，我们发现脯氨酸93的异构化与酪氨酸92的荧光变化有关。这提供了一种光谱探针，可用于监测未折叠后无序链中的这一过程及其在缓慢重折叠过程中的逆转。在未折叠的核糖核酸酶中，在两种缓慢折叠的物种中都发现了脯氨酸93的不正确反式异构体。重折叠过程中该脯氨酸肽键异构化的反式到顺式逆转显示出与天然蛋白形成的时间进程相同的动力学。脯氨酸93的异构化比在主要缓慢重折叠途径上积累的类似天然折叠中间体的形成要慢。文中讨论了解释这些结果的模型。
