Ascorbic acid may not be involved in cryptochrome-based magnetoreception
Journal of the Royal Society Interface
© 2017 The Author(s). Published by the Royal Society. All rights reserved.
Seventeen years after it was originally suggested, the photoreceptor protein cryptochrome remains the most probable host for the radical pair intermediates that are thought to be the sensors in the avian magnetic compass. Although evidence in favour of this hypothesis is accumulating, the intracellular interaction partners of the sensory protein are still unknown. It has been suggested that ascorbate ions could interact with surface-exposed tryptophan radicals in photoactivated cryptochromes, and so lead to the formation of a radical pair comprised of the reduced form of the flavin adenine dinucleotide cofactor, FAD•-, and the ascorbate radical, Asc•- This species could provide a more sensitive compass than a FAD-tryptophan radical pair. In this study of Drosophila melanogaster cryptochrome and Erithacus rubecula (European robin) cryptochrome 1a, we use molecular dynamics simulations to characterize the transient encounters of ascorbate ions with tryptophan radicals in cryptochrome in order to assess the likelihood of the [FAD•- Asc•-]-pathway. It is shown that ascorbate ions are expected to bind near the tryptophan radicals for periods of a few nanoseconds. The rate at which these encounters happen is low, and it is therefore concluded that ascorbate ions are unlikely to be involved in magnetoreception if the ascorbate concentration is only of the order of 1 mM or less.
This work was supported by the European Research Council (under the European Union's 7th Framework Programme, FP7/2007–2013/ERC Grant 340451) and the US Air Force (USAF) Office of Scientific Research (Air Force Materiel Command, USAF Award FA9550-14-1-0095). I.A.S. and C.N. are grateful to the Lundbeck Foundation for financial support. Computational resources for the simulations were provided by the DeiC National HPC Center, SDU.
This is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this record.
Vol. 14 (137), article 20170657
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