Ilia Solov'yov, Tatiana Domratcheva, and Klaus Schulten. Separation of photo-induced radical pair in cryptochrome to a functionally critical distance. Scientific Reports, 4:3845, 2014. (8 pages). (PMC:  PMC4894384)

SOLO2014 Animals and plants, together with other life forms, possess internal clocks that attune them to the daily rhythm on Earth. A key blue-light receptor serving for this purpose is a protein called cryptochrome. An apparent second role of cryptochrome is that of a sensor for the Earth's magnetic field, which helps migratory birds in long-range navigation. The latter function of cryptochrome arises from a light-induced reduction of its flavin cofactor through step-wise electron transfer involving several tryptophan amino acid residues. Here, this electron transfer is investigated by combining quantum-chemical and classical molecular dynamics calculations. The results reveal that the transfer occurs in tandem with key rearrangements in the cryptochrome structure in the vicinity of the polar environment of the protein's tryptophan residues and that a second transfer step can extend electron - - hole separation before the state reached in a first transfer step becomes stabilized through proton transfer. A large electron-hole separation extends the life time of the reduced state of cryptochrome's flavin cofactor and, thereby, extends receptor signaling as well as increases the signaling's sensitivity to the geomagnetic field.


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