On the quest of a biological compass: magnetic field effects on the cryptochrome protein – BIOMAGNET

Certain migratory animals orient during their long-distance migrations by perceiving the terrestrial magnetic field. The exact molecular origin of such sense is still unknown. Recently, the cryptochrome protein has been proposed as responsible of such "biological compass". The photochemical mechanism would be based on the radical pair creation in donor-acceptor complexes: after light absorption, an electron transfer occurs between one flavin and the tryptophans forming the active site of cryptochrome, generating in this way a localized radical pair. Such radical pair would undergo a coherent dynamics of populations of singlet and triplet excited states. Theoretical models have shown that such dynamics can be affected by low-intensity external magnetic fields, supposing that the excited states have specific magnetic and dynamical properties: long-lived radical pairs, different singlet and triplet reactivity, anisotropic hyperfine coupling, etc. To this point, there is no proof that such a mechanism can exist in a biological medium. We propose to develop a multi-scale quantum dynamical model with the objective of determining the effect of magnetic fields to the activity of the cryptochrome protein. This model is based on analytic effective Hamiltonians, which contain the information of magnetic, electronic and vibrational properties of the excited states of the protein. Such Hamiltonians will be used subsequently to propagate wavepackets in real time under the action of external magnetic fields. The project will give a first proof of whether the cryptochrome protein can be considered as a biological compass. Furthermore, the results can constitute the first direct proof of the effect of a low-intensity magnetic field on the mechanism of a photochemical reaction taking place in a biological medium.