Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya, 466-8555, Japan.
J Phys Chem B. 2012 May 24;116(20):5888-99. doi: 10.1021/jp302357m. Epub 2012 May 11.
Photoactive proteins with cognate chromophores are widespread in organisms, and function as light-energy converters or receptors for light-signal transduction. Rhodopsins, which have retinal (vitamin A aldehyde) as their chromophore within their seven transmembrane α-helices, are classified into two groups, microbial (type-1) and animal (type-2) rhodopsins. In general, light absorption by type-1 or type-2 rhodopsins triggers a trans-cis or cis-trans isomerization of the retinal, respectively, initiating their photochemical reactions. Recently, we found a new microbial rhodopsin (middle rhodopsin, MR), binding three types of retinal isomers in its original state: all-trans, 13-cis, and 11-cis. Here, we identified the absolute absorption spectra of MR by a combination of high performance liquid chromatography (HPLC) and UV-vis spectroscopy under varying light conditions. The absorption maxima of MR with all-trans, 13-cis, or 11-cis retinal are located at 485, 479, and 495 nm, respectively. Their photocycles were analyzed by time-resolved laser spectroscopy using various laser wavelengths. In conclusion, we propose that the photocycles of MR are MR(trans) → MR(K):lifetime = 93 μs → MR(M):lifetime = 12 ms → MR, MR(13-cis) → MR(O-like):lifetime = 5.1 ms → MR, and MR(11-cis) → MR(K-like):lifetime = 8.2 μs → MR, respectively. Thus, we demonstrate that a single photoactive protein drives three independent photochemical reactions.
具有生色团的光活性蛋白在生物中广泛存在，它们作为光能转换器或光信号转导受体发挥作用。视蛋白，其七跨膜α螺旋内的生色团为视黄醛（维生素 A 醛），分为微生物（1 型）和动物（2 型）视蛋白两类。一般来说，1 型或 2 型视蛋白吸收光分别引发视黄醛的反式顺式或顺式反式异构化，从而引发其光化学反应。最近，我们发现了一种新型微生物视蛋白（中视蛋白，MR），在其原始状态下结合三种类型的视黄醛异构体：全反式、13-顺式和 11-顺式。在这里，我们通过高效液相色谱（HPLC）和紫外可见光谱在不同光照条件下组合鉴定了 MR 的绝对吸收光谱。MR 与全反式、13-顺式或 11-顺式视黄醛结合的吸收最大值分别位于 485、479 和 495nm。我们通过使用各种激光波长的时间分辨激光光谱分析了它们的光循环。总之，我们提出 MR 的光循环为 MR(trans) → MR(K)：寿命=93μs → MR(M)：寿命=12ms → MR、MR(13-cis) → MR(O-like)：寿命=5.1ms → MR 和 MR(11-cis) → MR(K-like)：寿命=8.2μs → MR，分别。因此，我们证明了单个光活性蛋白驱动三种独立的光化学反应。
