1 research outputs found
Temperature Independence of Ultrafast Photoisomerization in Thermophilic Rhodopsin: Assessment versus Other Microbial Proton Pumps
Primary photochemical events in the
unusually thermostable proton
pumping rhodopsin of <i>Thermus thermophilus</i> 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 <i>Gloeobacter</i> 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