Cryptochrome magnetoreception: four tryptophans could be better than three

Area of Science:

• * Biophysics
• * Molecular Biology
• * Ornithology

Background:

• * Cryptochrome (Cry) proteins in bird eyes are hypothesized to function as magnetic compass sensors.
• * Photo-induced radical pairs within Cry proteins are believed to mediate magnetoreception.
• * Avian Cry4a is the most probable candidate for magnetic sensing, involving a chain of four tryptophan residues.

Purpose of the Study:

• * To investigate the dynamic equilibrium between two specific radical pair states in Cry4a.
• * To explore how these states contribute to magnetic sensing and signaling.
• * To understand the evolutionary implications of Cry4a's structure in avian magnetoreception.

Main Methods:

• * Purification of Cry4a from the European robin.
• * Spin dynamics simulations to model radical pair behavior.
• * Analysis of magnetic sensitivity and kinetic properties of radical pair states.

Main Results:

• * The third flavin-tryptophan radical pair in Cry4a exhibits higher magnetic sensitivity than the fourth.
• * Spin dynamics simulations suggest a rapid equilibrium between the third and fourth radical pair states.
• * The third radical pair is implicated in magnetic sensing, while the fourth may facilitate signaling.

Conclusions:

• * A dynamic equilibrium between Cry4a radical pair states allows for independent optimization of sensing and signaling.
• * The proposed mechanism provides a rationale for the four-tryptophan structure in avian Cry4a.
• * This model enhances understanding of the biophysical basis of avian magnetic navigation.