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首页> 外文期刊>Biochemistry >Protein folding intermediates with rapidly exchangeable amide protons contain authentic hydrogen-bonded secondary structures.
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Protein folding intermediates with rapidly exchangeable amide protons contain authentic hydrogen-bonded secondary structures.

机译：具有可快速交换的酰胺质子的蛋白质折叠中间体包含可靠的氢键键合二级结构。

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摘要

Recent studies on protein folding intermediates by pulsed amide proton exchange and by far-ultraviolet circular dichroism have shown important discrepancies between the secondary structure contents estimated by these two methods at early folding stages. To solve these apparent discrepancies, structural studies have been performed on the isolated, 101 residue long, C-terminal proteolytic domain (F2) of the Escherichia coli tryptophan synthase beta chain, which had previously been reported to behave as an early folding intermediate [Chaffotte, A. F., Cadieux, C., Guillou, Y., & Goldberg, M. E. (1992) Biochemistry 31, 4303-4308]. The secondary structure of F2 has been investigated by far-UV circular dichroism (CD), Fourier transform infrared (FTIR) spectroscopy, and NMR. The CD and FTIR spectra clearly indicate that isolated F2 has about 30-45% of its residues involved in secondary structures stabilized by conventional hydrogen bonds. The characteristics of the NMR spectrum (line broadening, absence of structure-induced chemical shifts, absence of nuclear Overhauser effects in the amide region, few dipolar interactions between the side-chain protons) suggest that isolated F2 is oscillating between several conformations in rapid equilibrium. The rate of amide proton exchange has been studied by one-dimensional NMR, which indicates a significant extent of proton protection, with, however, protection factors that can be estimated to be at most 60 and more probably closer to 10. Thus, F2 appears to exist as a molten globule that exhibits very low amide proton protection and yet contains a large fraction of its residues involved in authentic secondary structures stabilized by hydrogen bonds. Such a state is likely to correspond to the earliest structured folding intermediates thus far characterized.
机译：通过脉冲酰胺质子交换和远紫外圆二色性对蛋白质折叠中间体的最新研究表明，在折叠初期，这两种方法估计的二级结构含量之间存在重要差异。为了解决这些明显的差异，已经对大肠杆菌色氨酸合酶β链的101个残基长的C末端蛋白水解域（F2）进行了结构研究，该结构以前据报道表现为早期折叠中间体[Chaffotte ，AF，Cadieux，C.，Guillou，Y。，＆Goldberg，ME（1992）Biochemistry 31，4303-4308]。 F2的二级结构已通过远紫外圆二色性（CD），傅立叶变换红外（FTIR）光谱和NMR进行了研究。 CD和FTIR光谱清楚地表明，分离的F 2具有约30-45％的残基，所述残基涉及通过常规氢键稳定的二级结构。 NMR谱图的特征（谱线加宽，不存在结构诱导的化学位移，酰胺区域不存在核Overhauser效应，侧链质子之间几乎没有偶极相互作用）表明分离的F2在快速平衡的几个构象之间振荡。已通过一维NMR研究了酰胺质子交换的速率，这表明质子保护的程度很大，但是，保护因子估计最多为60，更可能接近10。因此，F2出现了。以熔融小球形式存在，它显示出非常低的酰胺质子保护性，但仍含有大部分残基，这些残基涉及通过氢键稳定的真正二级结构。这种状态很可能对应于迄今为止表征的最早的结构化折叠中间体。

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