The sensitivity of a radical pair compass magnetoreceptor can be significantly amplified by radical scavengers

TL;DR

This paper proposes a new model for avian magnetic sensing involving radical scavengers, which significantly enhances sensitivity and allows for greater radical separation, expanding the potential biological structures capable of magnetic detection.

Contribution

The study introduces a radical scavenger-based model that improves magnetic sensitivity and relaxes spatial constraints on radical pairs in cryptochrome proteins.

Findings

Sensitivity to magnetic fields is greatly increased.

Radicals can be more than 2 nm apart in the receptor.

The model reduces effects of radical interactions.

Abstract

Birds have a remarkable ability to obtain navigational information from the Earth's magnetic field. The primary detection mechanism of this compass sense is uncertain but appears to involve the quantum spin dynamics of radical pairs formed transiently in cryptochrome proteins. We propose here a new version of the current model in which spin-selective recombination of the radical pair is not essential. One of the two radicals is imagined to react with a paramagnetic scavenger via spin-selective electron transfer. By means of simulations of the spin dynamics of cryptochrome-inspired radical pairs, we show that the new scheme offers two clear and important benefits. The sensitivity to a 50 {\mu}T magnetic field is greatly enhanced and, unlike the current model, the radicals can be more than 2 nm apart in the magnetoreceptor protein. The latter means that animal cryptochromes that have a tetrad (rather than a triad) of tryptophan electron donors can still be expected to be viable as magnetic compass sensors. Lifting the restriction on the rate of the spin-selective recombination reaction also means that the detrimental effects of inter-radical exchange and dipolar interactions can be minimised by placing the radicals much further apart than in the current model.