Absorption Spectra and Photochemical Reactions in a Unique Photoactive Protein, Middle Rhodopsin MR

作者：Inoue Keiichi; Reissig Louisa; Sakai Makoto; Kobayashi Shiori; Homma Michio; Fujii Masaaki; Kandori Hideki; Sudo Yuki^*

来源：Journal of Physical Chemistry B, 2012, 116(20): 5888-5899.

DOI：10.1021/jp302357m

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 alpha-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) -%26gt; MRK:lifetime = 93 mu s -%26gt; MRM:lifetime = 12 ms -%26gt; MR, MR(13-cis) -%26gt; MRO-like:lifetime = 5.1 ms -%26gt; MR, and MR(11-cis) -%26gt; MRK-like:lifetime = 8.2 mu s -%26gt; MR, respectively. Thus, we demonstrate that a single photoactive protein drives three independent photochemical reactions.

• 出版日期2012-5-24