GLUTAMIC ACID-113 SERVES AS THE RETINYLIDENE SCHIFF-BASE COUNTERION IN BOVINE RHODOPSIN
GLUTAMIC ACID-113 SERVES AS THE RETINYLIDENE SCHIFF-BASE COUNTERION IN BOVINE RHODOPSIN
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DOI：
10.1073/pnas.86.21.8309
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发表时间：
1989-11-01
影响因子：
11.1
通讯作者：
KHORANA, HG
中科院分区：
文献类型：
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作者：
SAKMAR, TP;FRANKE, RR;KHORANA, HG
视觉色素吸收光的特征波长由蛋白质(视蛋白)和视黄基希夫碱发色团之间的相互作用调节。通过定点突变，系统地替换了牛视紫红质跨膜螺旋C中的带电氨基酸。谷氨酸-134或精氨酸-135的取代不影响光谱性质。然而，谷氨酰胺或天冬氨酸取代谷氨酸-122形成了光吸收蓝移的色素(最大吸收波长分别为480 nm和475 nm)。谷氨酸-113被天冬氨酸取代得到轻微红移的色素(最大吸收波长=505 nm)，而被谷氨酰胺取代得到的色素在光吸收方面发生了显著的蓝移(最大吸收波长=380 nm)。380 nm的物种与490 nm的物种存在着依赖于pH的平衡，使得在酸性的pH下，所有的色素都被转化为最大吸收波长=490 nm。我们认为谷氨酸-113是视紫红质中的视黄亚甲基席夫碱拮抗剂。我们认为，这种视蛋白-发色团的相互作用是视觉色素中颜色调节的一般机制的一个例子。
The characteristic wavelength at which a visual pigment absorbs light is regulated by interactions between protein (opsin) and retinylidene Schiff base chromophore. By using site-directed mutagenesis, charged amino acids in bovine rhodopsin transmembrane helix C were systematically replaced. Substitution of glutamic acid-134 or arginine-135 did not affect spectral properties. However, substitution of glutamic acid-122 by glutamine or by aspartic acid formed pigments that were blue-shifted in light absorption (.lambda.max = 480 nm and 475 nm, respectively). While the substitution of glutamic acid-113 by aspartic acid gave a slightly red-shifted pigment (.lambda.max = 505 nm), replacement by glutamine formed a pigment that was strikingly blue-shifted in light absorption (.lambda.max = 380 nm). The 380-nm species existed in a pH-dependent equilibrium with a 490-nm species such that at acidic pH all of the pigment was converted to .lambda.max = 490 nm. We conclude that glutamic acid-113 serves as the retinylidene Schiff base counterion in rhodopsin. We believe that this opsin-chromophore interaction is an example of a general mechanism of color regulation in the visual pigments.