title: Temperature Independence of Ultrafast Photoisomerization in Thermophilic Rhodopsin: Assessment versus Other Microbial Proton Pumps.
abstract: Primary photochemical events in the unusually thermostable proton pumping rhodopsin of Thermus thermophilus bacterium (TR) are reported for the first time. Internal conversion in this protein is shown to be significantly faster than in bacteriorhodopsin (BR), making it the most rapidly isomerizing microbial proton pump known. Internal conversion (IC) dynamics of TR and BR were recorded from room temperature to the verge of thermal denaturation at 70 °C and found to be totally independent of temperature in this range. This included the well documented multiexponential nature of IC in BR, suggesting that assignment of this to ground state structural inhomogeneity needs revision. TR photodynamics were also compared with that of the phylogenetically more similar proton pump Gloeobacter rhodopsin (GR). Despite this similarity GR has poor thermal stability, and the excited state decays significantly more slowly and exhibits very prominent stretched exponential behavior. Coherent torsional wave-packets induced by impulsive photoexcitation of TR and GR show marked resemblance to each other in frequency and amplitude and differ strikingly from similar signatures in pump-probe data of BR and other microbial retinal proteins. Possible correlations between IC rates and thermal stability and the promise of using torsional coherence signatures for understanding chromophore protein binding in microbial retinal proteins are discussed.
authors: Institute of Chemistry, The Hebrew University of Jerusalem , Jerusalem 9190501, Israel.
authors: E Siva Subramaniam
authors: ES
authors: Iyer
authors: Department of Organic Chemistry, The Weizmann Institute of Science , Rehovot 7610001, Israel.
authors: Ramprasad
authors: R
authors: Misra
authors: Institute of Chemistry, The Hebrew University of Jerusalem , Jerusalem 9190501, Israel.
authors: Arnab
authors: A
authors: Maity
authors: Institute of Chemistry, The Hebrew University of Jerusalem , Jerusalem 9190501, Israel.
authors: Oleg
authors: O
authors: Liubashevski
authors: Division of Pharmaceutical sciences, Okayama University , Kita-Ku, Okayama 700-0082, Japan.
authors: Yuki
authors: Y
authors: Sudo
authors: Department of Organic Chemistry, The Weizmann Institute of Science , Rehovot 7610001, Israel.
authors: Mordechai
authors: M
authors: Sheves
authors: Institute of Chemistry, The Hebrew University of Jerusalem , Jerusalem 9190501, Israel.
authors: Sanford
authors: S
authors: Ruhman
mesh_terms: D001436:Bacteriorhodopsins / Q000235:genetics / Q000378:metabolism*; D055668:Photochemical Processes; D017494:Proton Pumps / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature; D016963:Thermus thermophilus / Q000737:chemistry / Q000378:metabolism*
chemical_list: D017494:Proton Pumps; D001436:Bacteriorhodopsins