Decrypting Cryptochrome:
Revealing the Molecular Identity
of the Photoactivation Reaction
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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