Multiple photocycles of channelrhodopsin
Multiple photocycles of channelrhodopsin
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DOI：
10.1529/biophysj.105.069716
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发表时间：
2005-12-01
影响因子：
3.4
通讯作者：
Gradmann, D
中科院分区：
文献类型：
--
作者：
Hegemann, P;Ehlenbeck, S;Gradmann, D
最近在莱茵衣藻中发现了两种具有内在离子电导的视紫红质。它们被命名为“通道视紫红质”ChR1和ChR2。两者都在非洲爪蟾卵母细胞中表达，并通过双电极电压钳技术对其性质进行了定性研究。ChR1对H+具有特异性，而ChR2则传导Na+、K+、Ca2+和胍。ChR2响应光的起始具有峰值电导，随后是较小的稳态电导。在第二次刺激时，峰值较小，并恢复到全尺寸更快，在高外部pH值。ChR1据报道，以响应与稳态电导，但在这里证明有一个峰值电导在高光强度太。我们定量分析了ChR1的光诱导电导，并开发了一个反应方案，描述了在各种光照条件下的光电流动力学。ChR1存在于两个暗态，D1和D2，光异构化的导电状态M1和M2，分别。暗适应的ChR1在D1中被完全抑制。M1在几毫秒内转换成D1，但另外与衰减到第二暗状态D2的第二导电状态M2平衡。因此，光适应ChR1代表D1和D2的混合物。D2在几分钟内热转化为D1，即，比两个光循环的任何反应都慢。
Two rhodopsins with intrinsic ion conductance have been identified recently in Chlamydomonas reinhardtii. They were named ``channelrhodopsins'' ChR1 and ChR2. Both were expressed in Xenopus laevis oocytes, and their properties were studied qualitatively by two electrode voltage clamp techniques. ChR1 is specific for H+, whereas ChR2 conducts Na+, K+, Ca2+, and guanidinium. ChR2 responds to the onset of light with a peak conductance, followed by a smaller steady-state conductance. Upon a second stimulation, the peak is smaller and recovers to full size faster at high external pH. ChR1 was reported to respond with a steady-state conductance only but is demonstrated here to have a peak conductance at high light intensities too. We analyzed quantitatively the light-induced conductance of ChR1 and developed a reaction scheme that describes the photocurrent kinetics at various light conditions. ChR1 exists in two dark states, D1 and D2, that photoisomerize to the conducting states M1 and M2, respectively. Dark-adapted ChR1 is completely arrested in D1. M1 converts into D1 within milliseconds but, in addition, equilibrates with the second conducting state M2 that decays to the second dark state D2. Thus, light-adapted ChR1 represents a mixture of D1 and D2. D2 thermally reconverts to D1 in minutes, i.e., much slower than any reaction of the two photocycles.