Time‐Resolved Energetics of Photoprocesses in Prokaryotic Phytochrome‐Related Photoreceptors |
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| Authors: | Aba Losi Hernán R. Bonomi Norbert Michael Kun Tang Kai‐Hong Zhao |
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| Affiliation: | 1. Department of Physics and Earth Science, University of Parma, Parma, Italy;2. Immunology and Molecular Microbiology Laboratory, Fundación Instituto Leloir, Buenos Aires, Argentina;3. Institut für Chemie, Technische Universit?t Berlin, Berlin, Germany;4. State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, China;5. Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany |
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| Abstract: | Time‐resolved photoacoustics (PA) is uniquely able to explore the energy landscape of photoactive proteins and concomitantly detects light‐induced volumetric changes (ΔV) accompanying the formation and decay of transient species in a time window between ca. 20 ns and 5 μs. Here, we report PA measurements on diverse photochromic bilin‐binding photoreceptors of prokaryotic origin: (1) the chromophore‐binding GAF3 domain of the red (R)/green (G) switching cyanobacteriochrome 1393 (Slr1393g3) from Synechocystis; (2) the red/far red (R/FR) Synechocystis Cph1 phytochrome; (3) full‐length and truncated constructs of Xanthomonas campestris bacteriophytochrome (XccBphP), absorbing up to the NIR spectral region. In almost all cases, photoisomerization results in a large fraction of energy dissipated as heat (up to 90%) on the sub‐ns scale, reflecting the low photoisomerization quantum yield (<0.2). This “prompt” step is accompanied by a positive ΔV1 = 5–12.5 mL mol?1. Formation of the first intermediate is the sole process accessible to PA, with the notable exception of Slr1393g3‐G for which ΔV1 = +4.5 mL mol?1 is followed by a time‐resolved, energy‐conserving contraction ΔV2 = ?11.4 mL mol?1, τ2 = 180 ns at 2.4°C. This peculiarity is possibly due to a larger solvent occupancy of the chromophore cavity for Slr1393g3‐G. |
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