Migrating birds fly thousand miles and more, often without visual cues and in treacherous winds, yet keep direction. They employ for this purpose, apparently, as a powerful navigational tool the photoreceptor protein cryptochrome to sense the geomagnetic field. The unique biological function of cryptochrome must arise from the photoactivation reaction occurring in the protein: exposure to blue light results in electron transfer to a flavin pigment co-factor, leading to formation of an electron spin-entangled pair of radicals. Theoretical and experimental studies established long ago that such radical pairs, indeed, can act as a magnetic compass. The photo-reaction pathway in cryptochrome is not fully resolved yet. We employ ab initio quantum chemistry and classical all-atom MD simulations for Arabidopsis thaliana cryptochrome to determine how the radical pair is formed, becomes stabilized through proton transfer, and how it decays back to the protein's resting state.
Journal of the American Chemical Society, 2012, Vol 134, p. 18046-18052