Mechanism of activation of sensory rhodopsin I: evidence for a steric trigger.
Mechanism of activation of sensory rhodopsin I: evidence for a steric trigger.
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DOI：
10.1073/pnas.88.21.9412
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发表时间：
1991-11
影响因子：
11.1
通讯作者：
B. Yan;K. Nakanishi;J. Spudich
中科院分区：
文献类型：
--
作者：
B. Yan;K. Nakanishi;J. Spudich
来自盐生盐杆菌的感觉视紫红质I（SR-I）和细菌视紫红质（BR）显示出广泛的结构和光谱相似性，但执行不同的功能：分别是感光接收和质子泵。探测SR-I和BR与24个视网膜类似物的光活性位点揭示了视网膜13-甲基基团附近和β-紫罗兰酮环附近的蛋白质环境的差异。13-顺式-视黄醇不与SR-I脱辅基蛋白形成亚视黄醇色素，尽管该异构体与BR脱辅基蛋白的结合甚至比全反式-视黄醇（两种色素的功能异构体）更快。SR-I和BR的激活都需要全反式/13-顺式异构化的视黄醇;然而，需要的空间相互作用的视黄醇13-甲基基团和蛋白质之间的SR-I的激活，但不是BR。这些结果揭示了SR-I和BR之间的关键差异，这可能是它们的光活化途径中的初始分歧点。我们提出13-甲基-蛋白质相互作用作为SR-I激活的触发器-即，通过发色团将光子吸收转化为蛋白质构象变化。一个类似的空间触发器是必不可少的哺乳动物视紫红质的激活，表明在古细菌和脊椎动物的亚视黄光传感器的受体激活的共同机制。
Sensory rhodopsin I (SR-I) and bacteriorhodopsin (BR) from Halobacterium halobium show broad structural and spectroscopic similarities and yet perform distinct functions: photosensory reception and proton pumping, respectively. Probing the photoactive sites of SR-I and BR with 24 retinal analogs reveals differences in the protein environments near the retinal 13-methyl group and near the beta-ionone ring. 13-cis-Retinal does not form a retinylidene pigment with the SR-I apoprotein, although this isomer binds to the BR apoprotein even more rapidly than all-trans-retinal, the functional isomer of both pigments. The activation of both SR-I and BR requires all-trans/13-cis isomerization of retinal;however, a steric interaction between the retinal 13-methyl group and the protein is required for SR-I activation but not for that of BR. These results reveal a key difference between SR-I and BR that is likely to be the initial diverging point in their photoactivation pathways. We propose the 13-methyl group-protein interaction functions as a trigger for SR-I activation--i.e., converts photon absorption by the chromophore into protein conformational changes. A similar steric trigger is essential for activation of mammalian rhodopsin, indicating a common mechanism for receptor activation in archaebacterial and vertebrate retinylidene photosensors.