HISTIDINE-RESIDUES REGULATE THE TRANSITION OF PHOTOEXCITED RHODOPSIN TO ITS ACTIVE CONFORMATION, METARHODOPSIN-II
HISTIDINE-RESIDUES REGULATE THE TRANSITION OF PHOTOEXCITED RHODOPSIN TO ITS ACTIVE CONFORMATION, METARHODOPSIN-II
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DOI：
10.1016/0896-6273(92)90274-h
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发表时间：
1992-03-01
期刊：
影响因子：
16.2
通讯作者：
NATHANS, J
中科院分区：
文献类型：
--
作者：
WEITZ, CJ;NATHANS, J
视紫红质的生物活性光产物，变视紫红质II（M II），与其前体，变视紫红质I（M I）存在于pH敏感的平衡中。增加酸度有利于M II，pH滴定曲线的中点为pH 6.4。为了测试长期以来的建议，组氨酸质子化调节这种构象转变，我们的特点是突变视紫红质中的6个组氨酸被苯丙氨酸或半胱氨酸取代。只有在3个保守的组氨酸取代的突变体表现出异常的M I-M II平衡。那些在His-211被苯丙氨酸或半胱氨酸取代形成很少或没有M II在任何极端的pH值，而突变体取代在His-65或在His-152表现出增强的敏感性质子。这些结果的最简单的解释是，His-211是质子化强烈稳定的M II构象和His-65和His-152是质子化适度不稳定的M II构象的网站。
The biologically active photoproduct of rhodopsin, metarhodopsin II (M II), exists in a pH-sensitive equilibrium with its precursor, metarhodopsin I (M I). Increasing acidity favors M II, with the midpoint of the pH titration curve at pH 6.4. To test the long-standing proposal that histidine protonation regulates this conformational transition, we characterized mutant rhodopsins in which each of the 6 histidines was replaced by phenylalanine or cysteine. Only mutants substituted at the 3 conserved histidines showed abnormal M I-M II equilibria. Those in which His-211 was replaced by phenylalanine or cysteine formed little or no M II at either extreme of pH, whereas mutants substituted at His-65 or at His-152 showed enhanced sensitivity to protons. The simplest interpretation of these results is that His-211 is the site where protonation strongly stabilizes the M II conformation and that His-65 and His-152 are sites where protonation modestly destabilizes the M II conformation.