What Computational Simulations Tell Us about Cryptochromes in Magnetoreception

The ability of migratory birds to orient using the Earth's magnetic field has been proposed to rely on a radical-pair mechanism operating within Cryptochrome 4, a blue-light flavoprotein. In this perspective, we review how computational approaches have shaped our molecular understanding of cryptochrome-based magnetoreception. We organize the discussion around the three steps that connect light absorption to a cellular signal: the photochemical step, in which light absorption by FAD drives a hole-hopping electron-transfer cascade along a conserved tryptophan tetrad; the spin-dependent step, in which the resulting radical pair interconverts between singlet and triplet states under the influence of the magnetic field; and the structural step, in which this transient information is converted into a long-lived signaling state. The early electron-transfer events are now described with growing confidence and appear conserved across avian orthologs, although the relative stability of the final radical-pair states remains debated. The spin-dependent step remains more problematic: once the fluctuations of the hyperfine couplings and a realistic number of nuclear spins are included, the predicted magnetic sensitivity at geomagnetic field intensities becomes very small, and explaining the magnitude of the effect is still a central open problem. The postactivation conformational dynamics, involving intrinsically disordered regions, remains the principal challenge. We suggest that atomistic multiscale modeling, integrated with artificial intelligence-based approaches, has become indispensable for connecting the conserved photochemistry to this downstream process.