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Dynamics and efficiency of photoswitching in biliverdin-binding phytochromes. | LitMetric

Dynamics and efficiency of photoswitching in biliverdin-binding phytochromes.

Photochem Photobiol Sci

Department of Mathematical, Physical and Computer Sciences, University of Parma, Parco Area delle Scienze 7/A, 43124 Parma, Italy.

Published: October 2019

AI Article Synopsis

  • The study investigates the light-driven transformations between two states of bacteriophytochromes (BphPs) that utilize biliverdin IXα as a chromophore, observed using time-resolved absorption spectroscopy.
  • BphPs can switch between a red absorbing state (Pr) and a far-red/near-infrared absorbing state (Pfr), showcasing unique properties compared to plant phytochromes, with examples including PstBphP1, PaBphP, and FphA.
  • The quantum yields for photoconversion between states are low (0.02-0.12 for Pr-to-Pfr), and while thermal recovery of photoproducts occurs, FphA exhibits thermal stability

Article Abstract

The light-driven conversions between the dark-adapted and the photoproduct state were recorded for bacteriophytochromes (BphP) carrying biliverdin IXα (BV) as chromophore by time-resolved absorption spectroscopy. BphPs can be photoswitched between a red absorbing (Pr, maximum at ca. 700 nm) and a far-red/near-infrared (Pfr, maximum at ca. 750 nm) absorbing state, thereby showing a considerable red-shift with respect to plant phytochromes. Representatives for BphPs studied here are: PstBphP1 from Pseudomonas syringae pv. tomato, for which Pfr is the photoproduct; the bathy-phytochrome PaBphP from Pseudomonas aeruginosa for which instead Pfr is the thermally stable parental state. The third BphP-like protein was FphA from the fungus Aspergillus nidulans, a eukaryotic protein also carrying BV as a chromophore, for which Pr is considered to be the dark-adapted state. All three BphPs show a canonical modular arrangement with a three-domain photosensory module (PAS-GAF-PHY) and a histidine-kinase (HK) signalling domain. The quantum yields for Pr-to-Pfr photoconversion are in the range 0.02-0.12, and 0.04-0.08 for the Pfr-to-Pr route. Photoproducts of both bacterial phytochromes thermally recovered in the dark, whereas for the fungal protein (FphA) both Pr and Pfr forms are thermally stable for days and could be interconverted only by selective irradiation. The photoinduced reactions of all three BV-phytochromes are in general kinetically less complex than those of plant phytochromes, with the notable exception of the Pr-to-Pfr route for PstBphP1. By contrast in the Pfr-to-Pr conversion of FphAN753 the final product is already formed during the very early steps of the process, without formation of any further intermediates: to our knowledge it is the first phytochrome showing this behavior. All three proteins investigated are weakly fluorescent in the Pr form, with a maximum fluorescence quantum yield of 0.02 (PaBphP), and have undetectable fluorescence in the Pfr state.

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Source
http://dx.doi.org/10.1039/c9pp00264bDOI Listing

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