Structural comparison of metarhodopsin II, metarhodopsin III, and opsin based on kinetic analysis of Fourier transform infrared difference spectra.
Structural comparison of metarhodopsin II, metarhodopsin III, and opsin based on kinetic analysis of Fourier transform infrared difference spectra.
复制标题
基于傅里叶变换红外差谱动力学分析的变视紫红质 II、变视紫红质 III 和视蛋白的结构比较。
DOI：
10.1016/s0006-3495(92)81700-9
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发表时间：
1992
影响因子：
3.4
通讯作者：
Braiman,MS
中科院分区：
文献类型：
--
作者：
Klinger,AL;Braiman,MS
在 20 摄氏度和三个不同 pH 值下完全漂白视紫红质 (rho) 样品后，以 30 秒的间隔测量傅里叶变换红外差值光谱。在每个 pH 值下，所有光谱都可以全局拟合两个指数衰减过程。使用分支单分子动力学模型，其中变视紫红质 II (meta II) 直接或通过变视紫红质 III (meta III) 水解为视蛋白和视网膜，我们计算了每个 pH 值下的 rho-->meta II、rho-->meta III 和 rho--> 视蛋白差异光谱，并获得了每个 pH 下微观速率常数的估计值。由于必须对meta II 衰变路径之间的分支比做出假设，因此我们计算的每个pH 下的rho-->meta III 差异谱中仍存在一些不确定性。然而，我们的数据覆盖了很长的时间范围，特别是在 pH 8 下获得的数据，对 meta III 的光谱及其结构产生了重大的新限制。 rho-->meta II 光谱显示在检查范围内 (pH 5.5–8) 没有显着的 pH 依赖性。然而，rho-->meta III 和 rho-->视蛋白光谱各自包含 pH 依赖性峰的有限子集，这些峰主要归因于可滴定氨基酸侧链。我们的观察结果可用于完善早期的结论，即视色素在meta II衰变过程中重新折叠为视紫红质样构象（Rothschild, K.J., J. Gillespie, and W.J. DeGrip. 1987 Biophys. J. 51:345–350）。大多数重折叠在 pH 值范围为 5.5 至 8 的情况下以相同的方式发生，无论元 II 是否衰变为元 III 还是视蛋白。 Meta II 显示出独特的光谱扰动，这些扰动主要归因于一些残基，可能包括三到四个天冬氨酸或谷氨酸和一个精氨酸。
Fourier transform infrared difference spectra were measured at 30-s intervals after a complete bleach of rhodopsin (rho) samples at 20 degrees C and three different pH values. At each pH, all of the spectra could be fit globally to two exponential decay processes. Using a branched unimolecular kinetic model in which metarhodopsin II (meta II) is hydrolyzed to opsin and retinal both directly and through metarhodopsin III (meta III), we calculated rho-->meta II, rho-->meta III, and rho-->opsin difference spectra at each of the pH values and obtained estimates for the microscopic rate constants at each pH. Because of assumptions that had to be made about the branching ratio between the meta II decay pathways, some uncertainties remain in our calculated rho-->meta III difference spectrum at each pH. Nevertheless, our data covering long time ranges, especially those obtained at pH 8, place significant new constraints on the spectrum of meta III and thus on its structure. The rho-->meta II spectrum shows no significant pH dependence over the range examined (pH 5.5–8). However, the rho-->meta III and rho-->opsin spectra each include a limited subset of pH-dependent peaks, which are mostly attributable to titratable amino acid side chains. Our observations can be used to refine an earlier conclusion that the visual pigment refolds to a rhodopsin-like conformation during meta II decay (Rothschild, K.J., J. Gillespie, and W.J. DeGrip. 1987 Biophys. J. 51:345–350). Most of this refolding occurs in the same way at pH values ranging from 5.5 to 8 and whether meta II decays to meta III or opsin. Meta II displays unique spectral perturbations that are mostly attributable to a few residues, probably including three to four aspartic or glutamic acids and an arginine.