Phototropins

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Phototropins are light receptors in plants. Their name is derived from their involvement in the regulation of phototropism . In addition to this function, they are also involved in the phototaxis of the chloroplasts and in the regulation of the opening of the stomata .

Phototropins, together with cryptochromes, belong to the light receptors of plants, which have their absorption maximum in the UV / blue range. That is why long-wave UV (UV-A: 320-400 nm) and blue light (400-500 nm) can be combined to form a photobiologically effective range.

Phototropins are genetically old proteins (approx. 120 kDa in size) and are derived from related molecules in bacteria . They contain two LOV domains ( Light Oxygen Voltage ). FMN ( flavin mononucleotide ), which binds to one LOV domain in each case, could be detected as the chromophore . a total of two FMNs can therefore be bound per phototropin. This enables a reversible structural change of the protein when irradiated with light of the effective spectral range.

After exposure to blue light, the conformation of the chromophore changes in such a way (photochemical cycle) that it is briefly covalently bound to its LOV domain via a cysteine. When it returns to its basic state, the bond is released and the chromophore can be excited again. The conformational change that occurs in this process enables ATP-dependent autophosphorylation at 9 locations in the area of ​​the LOV domains. Signal transduction is still being researched. It is probably regulated by the auxin distribution in the shoot.

In the model organism Arabidopsis thaliana (thale cress), two genes are known that code for phototropins (PHOT1 = npl , PHOT2 = nph ). These were found with the help of the nph mutant (non-phototropic hypocotyl); the second gene was later named non-phototropic hypocotyl-like. The corresponding two gene products overlap and complement each other in their functions.

literature

  • Schopfer, Peter; Brennicke, Axel: Plant Physiology , Elsevier Spectrum Academic Publishing House, Munich 2006.
  • E. Peter, B. Dick and SA Baeurle, Mechanism of signal transduction of the LOV2-Jα photosensor from Avena sativa, Nature Commun. 1: 122 (2010); doi : 10.1038 / ncomms1121