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Magnetic sensitivity of cryptochrome 4 from a migratory songbird


Night-migratory songbirds are remarkably proficient navigators1. Flying alone and often over great distances, they use various directional cues including, crucially, a light-dependent magnetic compass2,3. The mechanism of this compass has been suggested to rely on the quantum spin dynamics of photoinduced radical pairs in cryptochrome flavoproteins located in the retinas of the birds4,5,6,7. Here we show that the photochemistry of cryptochrome 4 (CRY4) from the night-migratory European robin (Erithacus rubecula) is magnetically sensitive in vitro, and more so than CRY4 from two non-migratory bird species, chicken (Gallus gallus) and pigeon (Columba livia). Site-specific mutations of ErCRY4 reveal the roles of four successive flavin–tryptophan radical pairs in generating magnetic field effects and in stabilizing potential signalling states in a way that could enable sensing and signalling functions to be independently optimized in night-migratory birds.

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Fig. 1: Purification, electron transfer pathway and photoreduction of European robin CRY4.
Fig. 2: Magnetic field effects on the yields of photoinduced radicals in CRY4 proteins.
Fig. 3: Electron paramagnetic resonance and optical spectroscopy of photoinduced FAD–Trp radical pairs in ErCRY4.
Fig. 4: Reaction scheme and simulated magnetic field effects for ErCRY4.

Data availability

The complete set of molecular dynamics simulation and quantum chemistry data (300 GB) can be downloaded from the University of Oldenburg repository: Specific molecular dynamics data can also be obtained directly from I.A.S. on request. Source data are provided with this paper.


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This work was supported by the Air Force Office of Scientific Research (Air Force Materiel Command, USAF award no. FA9550-14-1-0095, to P.J.H., H.M., C.R.T., S.R.M. and K.-W.K.); by the European Research Council (under the European Union’s Horizon 2020 research and innovation programme, grant agreement no. 810002, Synergy Grant: ‘QuantumBirds’, awarded to P.J.H. and H.M.); by the Office of Naval Research Global, award no. N62909-19-1-2045, to P.J.H., C.R.T. and S.R.M.; by the Deutsche Forschungsgemeinschaft (SFB 1372, ‘Magnetoreception and navigation in vertebrates’, project number: 395940726 to H.M., K.-W.K., I.A.S. and P.J.H., and GRK 1885, ‘Molecular basis of sensory biology’ to K.-W.K., I.A.S. and H.M.); by a DAAD (German Academic Exchange Service, Graduate School Scholarship Programme, ID 57395813) stipend to J.X.; by funding for G.M. from the SCG Innovation Fund; by the Electromagnetic Fields Biological Research Trust (to P.J.H., C.R.T. and S.R.M.); by the National Natural Science Foundation of China, grant no. 31640001, and the Presidential Foundation of Hefei Institutes of Physical Science, Chinese Academy of Sciences, grant no. BJZX201901 (to C.X.); and by the Lundbeck Foundation, the Danish Councils for Independent Research, and the Volkswagen Foundation (to I.A.S.). V.D. is grateful to the Clarendon Fund, University of Oxford. M.J.G. thanks the Biotechnology and Biological Sciences Research Council, grant number BB/M011224/1 and the Clarendon Fund. We acknowledge use of the Advanced Research Computing (ARC) facility of the University of Oxford. J.S.T. is an Investigator and Y.C. is a Research Specialist in the Howard Hughes Medical Institute. I.A.S. is grateful to the DeiC National HPC Center, University of Southern Denmark for computational resources. We thank B. Grünberg, I. Fomins, A. Günther and A. Einwich for laboratory assistance and for providing protein sequence information. J.X. thanks Y. Tan for training in protein expression and purification. We thank S. Chandler for mass spectrometry, S. Y. Wong for assistance with spin dynamics calculations, and W. Myers (CAESR, Engineering and Physical Sciences Research Council, grant no. EP/L011972/1) for obtaining a threefold improvement in the time-resolved electron paramagnetic resonance signal. We are grateful to the staff of the mechanical and electronic workshops in the Oxford Chemistry Department and at the University of Oldenburg.

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Authors and Affiliations



J.X., L.E.J., T.Z., M.K., K.B.H., S.R. and M.J.G. made particularly important experimental contributions. J.X. cloned wild-type ErCRY4 and all the mutants and developed the protocols for expression and purification of the proteins with FAD bound. J.X. and J.S. produced the protein samples. L.E.J. developed the continuous illumination experiment for studying photoreduction and the picosecond transient absorption experiment for measuring magnetic field effects, and recorded and interpreted data. T.Z. and M.J.G. developed the CRDS experiment for measuring magnetic field effects and recorded and interpreted data. M.K. developed the broadband cavity-enhanced absorption spectroscopy experiment for measuring magnetic field effects and recorded and interpreted data. S.R. and S.W. recorded and interpreted the EPR data. K.B.H. participated in all five of the above experiments and recorded and interpreted spectroscopic data. J.F., with K.B.H., recorded and interpreted some of the transient absorption data and all of the re-oxidation data. M.K. helped with the global analysis of the re-oxidation data. M.J.G., V.D., J.R.W. and P.D.F.M. made spectroscopic measurements of magnetic field effects. D.J.C.S. helped to develop the picosecond TA apparatus. J.L. and Y.W. performed spin dynamics calculations. T.L.P. and G.M. reproduced and helped to interpret the EPR data. A.S.G. recorded and interpreted mass spectra. M.B. expressed and purified chicken CRY4. M.H., S.H., G.D. and S.J.K. expressed and purified some of the ErCRY4 protein samples. Y.C., J.S.T. and J.X. expressed and purified pigeon CRY4. H.Y., H.W., K.-W.K., R.B. and C.X. provided advice on protein expression. I.A.S. performed molecular dynamics simulations and provided advice on cryptochrome structure and dynamics. L.E.J. had oversight of the organization and administration of the optical spectroscopy measurements. P.J.H., H.M., C.R.T. and S.R.M. conceived the study. P.J.H., H.M., C.R.T., S.R.M. and C.X. supervised the work. P.J.H. and H.M. wrote the manuscript, and all authors commented on the manuscript.

Corresponding authors

Correspondence to Ilia A. Solov’yov, Can Xie, Stuart R. Mackenzie, Christiane R. Timmel, Henrik Mouritsen or P. J. Hore.

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Xu, J., Jarocha, L.E., Zollitsch, T. et al. Magnetic sensitivity of cryptochrome 4 from a migratory songbird. Nature 594, 535–540 (2021).

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