title: Absorption spectra and photochemical reactions in a unique photoactive protein, middle rhodopsin MR.
abstract: 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.
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya, 466-8555, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.forename: Louisa
authors.initials: L
authors.lastname: Reissig
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakai
authors.forename: Shiori
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
authors.forename: Masaaki
authors.initials: M
authors.lastname: Fujii
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sudo
mesh_terms: D000042:Absorption; D002851:Chromatography, High Pressure Liquid; D007536:Isomerism; D055668:Photochemical Processes; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011994:Recombinant Proteins; D012243:Rhodopsin