The Secrets of Cryptochromes: Photoreceptors, Clock Proteins, and Magnetic Sensors

Abstract A class of light-activated proteins in the eyes of birds, called cryptochromes, are thought to act as the primary magnetic sensors allowing night-migratory songbirds to navigate over thousands of kilometers using the earth’s magnetic field. Having evolved from DNA-repairing photolyases, cryptochromes have redirected the energy from light to fuel a variety of other functions: as photoreceptors, as regulators of the circadian clock – and, in some species, most likely as sensors of the magnetic field. While the quantum effects of magnetic fields on cryptochromes are already being studied in detail, almost nothing is known about the signaling cascade involving cryptochrome as the primary receptor protein. Two different screening methods have identified potential interaction partners that suggest an involvement of the visual phototransduction pathway, the visual cycle, potassium channels or glutamate receptors, but more pioneering research is needed to unravel the signaling cascade responsible for transducing the magnetic signal.