title: Decrypting cryptochrome: revealing the molecular identity of the photoactivation reaction.
abstract: Migrating birds fly thousands of miles or 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 supposedly arises from a photoactivation reaction involving radical pair formation through electron transfer. Radical pairs, indeed, can act as a magnetic compass; however, the cryptochrome photoreaction pathway is not fully resolved yet. To reveal this pathway and underlying photochemical mechanisms, we carried out a combination of quantum chemical calculations and molecular dynamics simulations on plant ( Arabidopsis thaliana ) cryptochrome. The results demonstrate that after photoexcitation a radical pair forms, becomes stabilized through proton transfer, and decays back to the protein's resting state on time scales allowing the protein, in principle, to act as a radical pair-based magnetic sensor. We briefly relate our findings on  A. thaliana  cryptochrome to photoreaction pathways in animal cryptochromes.
authors.affiliation: Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, 405 N. Mathews Ave, Urbana, Illinois 61801, USA. ilia@illinois.edu
authors.forename: Ilia A
authors.initials: IA
authors.lastname: Solov'yov
authors.forename: Tatiana
authors.initials: T
authors.lastname: Domratcheva
authors.forename: Abdul Rehaman
authors.initials: AR
authors.lastname: Moughal Shahi
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
mesh_terms: D017360:Arabidopsis / Q000737:chemistry; D056931:Cryptochromes / Q000737:chemistry*; D004579:Electron Transport; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D055668:Photochemical Processes; D011522:Protons; D011789:Quantum Theory; D014364:Tryptophan / Q000737:chemistry
chemical_list: D056931:Cryptochromes; D011522:Protons; D014364:Tryptophan