Mechanism of magnetic field effect in cryptochrome

TL;DR

This paper proposes a detailed reaction cycle in cryptochrome that explains how magnetic fields influence bird magnetoreception, integrating experimental observations and offering insights into the structural features needed for geomagnetic sensing.

Contribution

It introduces a concrete light-driven reaction cycle in cryptochrome that links experimental data with the biological mechanism of avian magnetoreception.

Findings

Cryptochrome can feasibly act as a geomagnetic compass in birds.

The reaction cycle explains how magnetic fields influence cryptochrome signaling.

Structural and dynamic features are identified as crucial for magnetic field detection.

Abstract

Creatures as varied as mammals, fish, insects, reptiles, and migratory birds have an intriguing `sixth' sense that allows them to distinguish north from south by using the Earth's intrinsic magnetic field. Yet despite decades of study, the physical basis of this magnetic sense remains elusive. A likely mechanism is furnished by magnetically sensitive radical pair reactions occurring in the retina, the light-sensitive part of the eyes. A photoreceptor, cryptochrome, has been suggested to endow birds with magnetoreceptive abilities as the protein has been shown to exhibit the biophysical properties required for an animal magnetoreceptor to operate properly. Here, we propose a concrete light-driven reaction cycle in cryptochrome that lets a magnetic field influence the signaling state of the photoreceptor. The reaction cycle ties together transient absorption and electron-spin-resonance observations with known facts on avian magnetoreception. Our analysis establishes the feasibility of cryptochrome to act as a geomagnetic compass in birds, gives insight into structural and dynamic design features required for optimal detection of the geomagnetic field direction, and suggests further theoretical and experimental studies.