DETERMINANTS OF VISUAL PIGMENT ABSORBENCY - IDENTIFICATION OF THE RETINYLIDENE SCHIFF-BASE COUNTERION IN BOVINE RHODOPSIN
DETERMINANTS OF VISUAL PIGMENT ABSORBENCY - IDENTIFICATION OF THE RETINYLIDENE SCHIFF-BASE COUNTERION IN BOVINE RHODOPSIN
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DOI：
10.1021/bi00493a034
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发表时间：
1990-10-16
期刊：
影响因子：
2.9
通讯作者：
NATHANS, J
中科院分区：
文献类型：
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作者：
NATHANS, J
通过将天冬氨酸和谷氨酸分别突变为天冬酰胺和谷氨酰胺，测试了带负电荷的残基在调整牛视紫红质吸收光谱中的作用。先前的工作表明，天冬氨酸 83、谷氨酸 122 和谷氨酸 134 可以被中性残基取代，对所得色素的吸收光谱影响很小或没有影响 [Nathans, J. (1990) Biochemistry 29, 937-942]。除一个例外，其余 19 个天冬氨酸和谷氨酸残基的突变导致非常接近野生型的吸收光谱。谷氨酸113是个例外；谷氨酰胺突变导致色素在 380 nm 处吸附，反映亚视黄基席夫碱的去质子化。添加氯化物、溴化物或碘化物后，吸光度分别迅速转变为 495、498 或 504.5 nm，反映希夫碱的质子化。添加具有较大原子半径的卤化物后观察到的渐进红移强烈表明卤化物充当希夫碱抗衡离子。卤化物对野生型视紫红质的吸收光谱没有影响。因此，我推断谷氨酸 113 是野生型视紫红质中视黄亚基 Sciff 的基本抗衡离子。萨克马尔等人。 [(1989) 程序。国家。阿卡德。科学。 U.S.A. 86, 8309-8313] 以及 Zhukovsky 和 Oprian [(1989) Science 246, 928-930] 基于一系列相关实验得出了相同的结论。这些数据支持一个模型，其中牛视紫红质的光谱调谐是由 11-顺式视黄醛的多烯链与结合袋中不带电荷的氨基酸之间的相互作用引起的。
The role of negatively charged residues in tuning the absorbance spectrum of bovine rhodopsin has been tested by mutating each aspartate and glutamate to asparagine and glutamine, respectively. Previous work demonstrated that aspartate83, glutamate122, and glutamate134 can be replaced by neutral residues with little or no effect on the absorbance spectrum of the resulting pigment [Nathans, J. (1990) Biochemistry 29, 937-942]. With one exception, mutations at the remaining 19 aspartate and glutamate residues result in very nearly wild-type absorbance spectra. The exception is glutamate113; mutation to glutamine causes the pigment to adsorb at 380 nm, reflecting deprotonation of the retinylidene Schiff''s base. Upon addition of either chloride, bromide, or iodide, the absorbance rapidly shifts to 495, 498, or 504.5 nm, respectively, reflecting protonation to the Schiff''s base. The progressive red shift observed upon addition of halides with larger atomic radii strongly suggests that halides are serving as the Schiff''s base counterion. Halides have no effect on the absorbance spectrum of wild-type rhodopsin. I infer, therefore, that glutamate113 is the retinylidene Sciff''s base counterion in wild-type rhodopsin. Sakmar et al. [(1989) Proc. Natl. Acad. Sci. U.S.A. 86, 8309-8313] and Zhukovsky and Oprian [(1989) Science 246, 928-930] have arrived at the same conclusion based upon a related series of experiments. These data support a model in which spectral tuning in bovine rhodopsin results from interactions between the polyene chain of 11-cis-retinal and uncharged amino acids in the binding pocket.