Conformations of the active and inactive states of opsin
Conformations of the active and inactive states of opsin
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DOI：
10.1074/jbc.m105423200
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发表时间：
2001-10-19
影响因子：
4.8
通讯作者：
Siebert, F
中科院分区：
文献类型：
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作者：
Vogel, R;Siebert, F
视紫红质的信号状态视紫红质II降解为脱辅基蛋白视蛋白和全反式视网膜，然后由视觉周期再生为视紫红质。已知视蛋白在中性pH条件下对其G蛋白转导蛋白只有很小的残余结构活性，被认为在光适应(漂白脱敏)中起着相当大的作用。在这项研究中，我们用傅里叶变换红外光谱表明，在羟胺清除内源性全反式视网膜的情况下，视黄素在变紫红质II衰退后，在30℃时以两种构象存在，处于pH依赖的平衡状态，pK值为4.1。尽管其结合口袋中缺乏天然的激动剂，但低pH视蛋白构象与变视紫质II非常相似，并且同样由视紫红质同源G蛋白转导蛋白衍生的多肽稳定。另一方面，高pH形式与不活跃的变紫红质I状态有一些构象相似之处。因此，我们得出结论，视蛋白载脂蛋白显示出仅受结合的全反式视网膜调节的固有构象状态。
The signaling state metarhodopsin II of the visual pigment rhodopsin decays to the apoprotein opsin and all-trans retinal, which are then regenerated to rhodopsin by the visual cycle. Opsin is known to have at neutral pH only a small residual constitutive activity toward its G protein transducin, which is thought to play a considerable role in light adaptation (bleaching desensitization). In this study we show with Fourier-transform infrared spectroscopy that after metarhodopsin II decay, opsin exists in two conformational states that are in a pH-dependent equilibrium at 30 degreesC with a pK of 4.1 in the presence of hydroxylamine scavenging the endogenous all-trans retinal. Despite the lack of the native agonist in its binding pocket, the low pH opsin conformation is very similar to that of metarhodopsin II and is likewise stabilized by peptides derived from rhodopsin's cognate G protein, transducin. The high pH form, on the other hand, has some conformational similarity to the inactive metarhodopsin I state. We therefore conclude that the opsin apoprotein displays intrinsic conformational states that are merely modulated by bound all-trans retinal.