Phototropin

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

Phototropins belong together with the cryptochromes to the light receptors of the plants which have their absorption maximum in the UV / blue range. So we can long -wave ultraviolet (UVA: 320-400 nm) summarize and blue light ( 400-500 nm ) to a photo biologically effective range.

Phototropins are phylogenetically old proteins (approximately 120 kDa ) and are derived from related molecules in bacteria. They contain two LOV domains (Light - Oxygen -Voltage). As chromophore could FMN ( flavin mononucleotide ) demonstrated that binds a LOV domain at a time. Overall, therefore, two FMN per Phototropin can be bound. This will light the effective spectral range enables irradiation in a reversible structural change of the protein.

After blue-light irradiation, the conformation of the chromophore in such a way ( photochemical cycle ), it is briefly covalently linked via a cysteine ​​at its LOV domain changes. If it goes back to the ground state, dissolves the bond and the chromophore can be excited again. The conformational change that is created, allowing the ATP-dependent autophosphorylation at 9 locations in the LOV domains. The signal transduction is still being researched. Probably it is regulated by the auxin distribution in the shoot.

In the model organism Arabidopsis thaliana ( thale cress ) two genes are known that encode phototropins ( phot1 = npl, phot2 = nph ). These were using the nph mutant ( non -photo tropic hypocotyl ) found; the second gene was later called non -photo tropic hypocotyl -like. The corresponding gene products both overlap and complement each other in their functions.