Darmstadt 2008 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 25: Laseranwendungen (Spektroskopie)
Q 25.3: Talk
Tuesday, March 11, 2008, 17:00–17:15, 3H
Photo Dynamics of BLUF domain mutant H44R of AppA from Rhodobacter sphaeroides — •Peyman Zirak1, Alfons Penzkofer1, Peter Hegemann2, and Thilo Mathes2 — 1Institut II - Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstrasse 31, D-93053 Regensburg, Germany — 2Institut für Biologie, Experimentelle Biophysik, Humboldt-Universität zu Berlin, Invalidenstr.42, D-10115 Berlin
The photo-cycle dynamics of the H44R mutant of the BLUF domain of the protein AppA (AppA-H44R) from the purple bacterium Rhodobacter sphaeroides is studied. The amino acid residue histidine at position 44 is replaced by arginine. A 12 nm red-shifted signalling state is formed upon blue-light excitation, while in wild-type AppA (AppA-wt) the red-shift is 16 nm. The recovery time to the receptor dark state is 6.5 min. It is approximately a factor of 2.5 faster than the recovery of the wild-type counterpart. Extended light exposure of the mutant causes photo-degradation of flavin (mainly flavin conversion to lumichrome). No photo-degradation was observed for AppA-wt. The quantum efficiency of signalling state formation determined by intensity dependent absorption measurements is found to be 0.3 (for AppA-wt: 0.24). A two-component single-exponential fluorescence relaxation was observed with lifetimes of 80 ps and 900 ps (for AppA-wt: 1.3 ps and 270 ps), which is interpreted as fast fluorescence quenching to an equilibrium by photo-induced electron transfer followed by slower fluorescence decay due to charge recombination. Based on the experimental findings, a photo-cycle model for BLUF domains is proposed.