What makes red visual pigments red? A resonance Raman microprobe study of retinal chromophore structure in iodopsin.
What makes red visual pigments red? A resonance Raman microprobe study of retinal chromophore structure in iodopsin.
复制标题
是什么使红色视色素呈红色？
DOI：
10.1021/bi00174a023
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发表时间：
1994
期刊：
影响因子：
2.9
通讯作者：
Mathies,RA
中科院分区：
文献类型：
--
作者：
Lin,SW;Imamoto,Y;Fukada,Y;Shichida,Y;Yoshizawa,T;Mathies,RA
摘要：我们获得了鸡视锥细胞中一种红敏色素碘视蛋白的共振拉曼光谱，以研究视蛋白位移的分子机制。用拉曼微探针检查洗涤剂溶解的碘视蛋白样品，以获得由11-ds-碘视蛋白及其9-顺式-异碘视蛋白和N-反式-红碘视蛋白光产物组成的77-K光稳态混合物的光谱。这些物种的振动模式已被分配与相应的牛色素的光谱比较。牛，蟾蜍，和鸡的色素的单键伸缩频率被发现表现出一个规则的相关性作为一个功能的色素吸收最大值，这是符合预期的影响，增加电子离域。碘视素和红碘视素的C= NH伸缩频率分别在1644和1638 cm-1，当氮被氘代时，分别下移至1621和1617 cm-1。发现各种色素的C= ND伸缩频率随着最大吸收值的增加而线性降低，这表明视觉色素中的视蛋白移位至少有一部分是由于视网膜发色团与其蛋白质之间的静电相互作用减弱所致。拉曼数据与带电荷的蛋白质残基沿着发色团移动沿着以调节视蛋白移动的想法不一致。与诱变和模型化合物结果一起，这些共振拉曼数据表明，绿色和红色视锥细胞视色素之间的视蛋白移位由两种效应引起。首先，Tyr-274提供了增加的席夫碱-抗衡离子对的静电稳定性。第二，通过偶极残基Ser-177和Thr-282增强视蛋白位移，所述偶极残基与紫罗酮环附近的发色团相互作用以优先稳定电子激发的视网膜发色团的高度偶极电荷分布[Mathies，R.，& Stryer，L.等人（1976）Proc. Acad. Sci. USA 73，2169-2173]。脊椎动物的色觉由视网膜的视锥细胞中的三种视色素介导，所述视色素在光谱的蓝色（~ 430 nm）、绿色（~ 530 nm）和红色（~ 560 nm）区域中吸收最大（Lythgoe，1972; Yoshizawa，1992）。负责昏暗光、黑白视觉的视杆细胞含有在500 nm处吸收最大的视紫红质。所有的视色素都由一个11-m-视网膜发色团组成，该发色团通过质子化席夫碱（PSB）1键与一个约40 000-Da的内在膜蛋白（称为视蛋白）上的保守赖氨酸残基共价连接。虽然质子化视黄酸席夫碱在~ 440
Revised Manuscript Received December 1, 1993® abstract: We have obtained resonance Raman spectra of iodopsin, a red-sensitive (Xmax 571 nm) pigment from chicken cone cells, to investigate the molecular mechanism of the opsin shift in visualpigments. Detergent-solubilized iodopsinsamples were examined with a Raman microprobe to obtain spectra from a 77-K photostationary steady-state mixture composed of 1 l-ds-iodopsin and its 9-c/j-isoiodopsin and a//-franj-bathoiodopsin photoproducts. The vibrational modes of these species have been assigned by comparison with spectra of the corresponding bovine pigments. The single bond stretching frequencies of the bovine, toad, and chicken pigments are found to exhibit a regular correlation as a function of the pigment absorption maxima that is consistent with the expected effects of increased electron delocalization. The C= NH stretching frequencies of iodopsin and bathoiodopsin are at 1644 and 1638 cm-1, respectively, and shift down to 1621 and 1617 cm-1, respectively, when the nitrogen is deuterated. The C= ND stretching frequencies of the various pigments are found to decrease linearly with increasing absorption maxima, suggesting that at least part of the opsin shift in visual pigmentsresults from weakened electrostatic interaction between the retinal chromophoreand its protein counterion. The Raman data are inconsistent with the idea that a charged protein residue is shifted along the chromophore to regulate the opsin shift. Taken together with the mutagenesis and model compound results, these resonance Raman data suggest that the opsin shift between the green and red cone visual pigments arises from two effects. First, Tyr-274 provides increased electrostatic stabilization of the Schiff base-counterion ion pair. Second, the opsin shift is enhanced by the dipolar residues Ser-177 and Thr-282 that interact with the chromophore near the ionone ring to preferentially stabilizethe highly dipolar charge distribution of the electronically excited retinal chromophore [Mathies, R., & Stryer, L.(1976) Proc. Natl. Acad. Sci. USA 73, 2169-2173].Color vision in vertebrates is mediated by three visual pigments in the cone cells of the retina that absorb maximally in the blue (~ 430 nm), green (~ 530 nm), and red (~ 560 nm) regions of the spectrum (Lythgoe, 1972; Yoshizawa, 1992). Rod cells which are responsible for dim-light, blackand-white vision contain rhodopsin absorbing maximally at 500 nm. All visual pigments consist of an 11-m-retinal chromophore that is covalently linked by a protonated Schiff base (PSB) 1 bond to a conserved lysine residue on a~ 40 000-Da intrinsic membrane protein called opsin. Although protonated retinalSchiff bases absorb maximally at~ 440