Temperature Independence of Ultrafast Photoisomerization in Thermophilic Rhodopsin: Assessment versus Other Microbial Proton Pumps

E. Siva Subramaniam Iyer, Ramprasad Misra, Arnab Maity, Oleg Liubashevski, Yuki Sudo, Mordechai Sheves, Sanford Ruhman

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)12401-12407
Number of pages7
JournalJournal of the American Chemical Society
Volume138
Issue number38
DOIs
Publication statusPublished - Sep 28 2016

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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