脯氨酸顺反异构化参与核糖核酸酶A缓慢解折叠反应的证据。
Evidence for involvement of proline cis-trans isomerization in the slow unfolding reaction of RNase A.
作者信息
Garel J R
出版信息
Proc Natl Acad Sci U S A. 1980 Feb;77(2):795-8. doi: 10.1073/pnas.77.2.795.
The three exposed tyrosines of RNase A have been converted to nitrotyrosines by reaction with tetranitromethane, and the changes in the ionization properties of these nitrotyrosines have been used to follow the kinetics of unfolding of the nitrated protein. It is found that the nitrotyrosines not only are sensitive to the overall disruption of the protein structure, which occurs in a faster reaction, but also serve as reporter groups for the slower reaction which takes place in the unfolded state. This slower reaction corresponds to the formation of the slow-refolding species of the unfolded protein. The kinetic properties of the slower reaction--guanidine-dependence of the rate and activation ethalpy--are similar to those of the proline cis-trans isomerization in a model peptide determined in the same conditions. It is concluded that proline cis-trans isomerization is indeed the rate-limiting factor for the formation of the slow-refolding species. Because the influence of proline cis-trans isomerization on the properties of the nitrotyrosines in the unfolded protein is probably due to a local effect, it is suggested that most of the optical changes observed during this slow unfolding reaction arise from the effect of the cis-trans isomerization of the Asn113-Pro114 bond on the properties of nitrotyrosine 115.
核糖核酸酶A（RNase A）的三个暴露的酪氨酸通过与四硝基甲烷反应已转化为硝基酪氨酸，并且这些硝基酪氨酸电离性质的变化已被用于追踪硝化蛋白质的解折叠动力学。研究发现，硝基酪氨酸不仅对蛋白质结构的整体破坏敏感（这种破坏发生在较快的反应中），而且还作为未折叠状态下较慢反应的报告基团。这种较慢的反应对应于未折叠蛋白质的慢折叠物种的形成。较慢反应的动力学性质——速率的胍依赖性和活化焓——与在相同条件下测定的模型肽中脯氨酸顺反异构化的动力学性质相似。得出的结论是，脯氨酸顺反异构化确实是慢折叠物种形成的限速因素。由于脯氨酸顺反异构化对未折叠蛋白质中硝基酪氨酸性质的影响可能是由于局部效应，因此表明在这种缓慢解折叠反应过程中观察到的大多数光学变化源于Asn113 - Pro114键的顺反异构化对硝基酪氨酸115性质的影响。
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