| 1. |
- Nöll, Gilbert, et al.
(författare)
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Redox properties of LOV domains: Chemical versus photochemical reduction, and influence on the photocycle
- 2007
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Ingår i: ChemBioChem. - : Wiley. - 1439-4227 .- 1439-7633. ; 8:18, s. 2256-2264
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Tidskriftsartikel (refereegranskat)abstract
- LOV (light-oxygen-voltoge-sensitive) domains comprise the lightsensitive parts of many blue light photoreceptor proteins. Photoexcitation of the chromophore flavin mononucleotide (FMN) in these LOV domains leads to formation of a covalent adduct between FMN and a cysteine residue. So for, the electronically excited singlet and triplet states of FMN have been identified as the only intermediates in the photocycles of LOV domains from several organisms. Since many flavoproteins ore redox-active, however, the photocycles of LOV domains might involve other redox states of FMN, and might be controlled by the external redox potential. Here we report on the redox properties of the LOV1 domain from phototropin of the green alga Chlamydomonas reinhardtii. By equilibrium-redox spectropotentiometry a redox potential [E-fq/fhq (flavoquinone/flavohydroquinone)] of -290 mV vs. the normal hydrogen electrode (NHE) was determined for the wild-type domain (LOV1-wt). A similar value of -280 mV was found for the mutant LOV1-C57G, in which the photoreactive cysteine is replaced by glycine. The recovery kinetics (photoadduct--> ground state) in the photocycle of LOV1-wt are not influenced by a redox potential in the range between +500 and -260 mV versus NHE. No flavosemiquinone could be generated by chemical reduction with sodium dithionite. However photoreduction of LOV1-C57G with EDTA leads exclusively to the flavosemiquinone. This semiquinone is stable against disproportionation, and the photoreduction is not mediated by free FMN.
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| 2. |
- Petroutsos, Dimitris, et al.
(författare)
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A blue-light photoreceptor mediates the feedback regulation of photosynthesis
- 2016
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 537:7621, s. 563-566
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Tidskriftsartikel (refereegranskat)abstract
- In plants and algae, light serves both as the energy source for photosynthesis and a biological signal that triggers cellular responses via specific sensory photoreceptors. Red light is perceived by bilin-containing phytochromes and blue light by the flavin-containing cryptochromes and/or phototropins (PHOTs)1, the latter containing two photosensory light, oxygen, or voltage (LOV) domains2. Photoperception spans several orders of light intensity3, ranging from far below the threshold for photosynthesis to values beyond the capacity of photosynthetic CO2 assimilation. Excess light may cause oxidative damage and cell death, processes prevented by enhanced thermal dissipation via high-energy quenching (qE), a key photoprotective response4. Here we show the existence of a molecular link between photoreception, photosynthesis, and photoprotection in the green alga Chlamydomonas reinhardtii. We show that PHOT controls qE by inducing the expression of the qE effector protein LHCSR3 (light-harvesting complex stress-related protein 3) in high light intensities. This control requires blue-light perception by LOV domains on PHOT, LHCSR3 induction through PHOT kinase, and light dissipation in photosystem II via LHCSR3. Mutants deficient in the PHOT gene display severely reduced fitness under excessive light conditions, indicating that the sensing, utilization, and dissipation of light is a concerted process that plays a vital role in microalgal acclimation to environments of variable light intensities.
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