The Earth is enveloped in a protective magnetic field that emanates from the planet's core. This invisible field passes through our atmosphere, mountains, oceans, houses and even our bodies. Though it is concealed from human sensation, many organisms can detect and make use of magnetic fields to inform navigation and migration behaviors. This ability is known as magnetosensing, and it has been a topic of neurobiological intrigue for several decades. There are hypotheses to explain how magnetic sensing works, but there has been little scientific validation of any mechanism. However, a recent study now provides new evidence for a putative magnetoreceptor that might explain how biological cells detect magnetic fields.

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Siying Qin (Peking University, China) and colleagues extensively screened the genome of fruit flies to identify a protein complex that is found in several species and is capable of interacting with magnetic fields (Nat. Mater. doi:10.1038/nmat4484; published online 16 November 2015). The protein complex they uncovered is composed of two main pieces. The first piece is a flavoprotein called cryptochrome that has long been implicated in magnetic sensing. The other piece is a novel component that the authors call MagR. MagR is a protein containing iron-sulphur clusters, which potentially act as the initial magnetosensors within the complex. Using imaging techniques and molecular modeling, the researchers determined that the protein complex appears as a rod-like string of MagR molecules surrounded by a double-helix of cryptochrome molecules.

Most importantly, the authors' work provides the first direct observation of a protein complex within biological tissue that is capable of detecting magnetic fields. In experiments using imaging during application of an external magnetic field, the authors show that MagR-cryptochrome molecules display physical rotational changes in the presence of strong magnetic fields. The researchers also show that these protein complexes are found in multiple animal species, including the retinas of pigeons, which are known to use the earth's geomagnetic field during navigation.

The combination of techniques used by the authors provides the best evidence to date that a magnetoreceptor molecule exists within magnetosensitive organisms, and might provide a molecular mechanism for this mysterious sensory system. Future studies are needed to confirm this novel mechanism, including electrophysiology to demonstrate that these protein complexes actually function as true receptors in neurons. If these molecules do function as magnetoreceptors, then these results could open up an entire new area of sensory neuroscience.