This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A collaborative research team led by Yasuhiro Kobori at Kobe University, together with researchers from Toho University, Saitama University, Nagoya Institute of Technology and the University of Freiburg, has identified a potential molecular mechanism that could enhance magnetic compass responses in cryptochrome, a blue-light-sensitive protein implicated in magnetoreception. Using time-resolved electron paramagnetic resonance (EPR) spectroscopy, the team identified structural rearrangements in light-induced intermediates and a contribution from chirality-induced spin selectivity (CISS).
Their analysis suggests that chiral rotational motion of a tryptophan residue can influence electron-spin polarization and enhance the directional dependence of downstream chemical reactions. Their findings are published in The Journal of Physical Chemistry Letters. Migratory birds and other organisms are thought to use Earth's magnetic field for directional information.
Cryptochrome contains flavin adenine dinucleotide (FAD), which absorbs blue light and initiates sequential electron transfer from tryptophan residues. The resulting charge-separated radical pairs have two unpaired electron spins whose singlet–triplet dynamics can depend on the external magnetic field. CISS links molecular chirality to preferential spin transport.
Whether motion within cryptochrome can produce this effect and influence a radical-pair compass has remained largely unexplored. The researchers examined Xenopus laevis cryptochrome-DASH using time-resolved EPR following pulsed laser excitation, at temperatures from −153 °C (−243°F) to −33 °C (−27°F). Quantum-mechanical simulations incorporated CISS, exchange coupling, electron–electron dipolar coupling and hyperfine interactions.
The spectra supported a structural rearrangement involving chiral rotation of the oxidized tryptophan WB(H)•+ in the second charge-separated state, FAD•−···WB(H)•+, with an estimated CISS contribution of 8%. A smaller contribution, no greater than 6%, was inferred for the longer-range FAD•−···WC(H)•+ state. The findings support transfer of spin coherence generated during the earlier charge-separation step to the terminal radical pair.
Calculations of the signaling-state reaction yield predicted a normalized anisotropy of approximately 0.3% without CISS. Including a 6% CISS contribution increased the predicted anisotropy to 1.6%. The model also predicted differences between responses to reversed magnetic-field directions, reflecting the coupling of chiral spin polarization to radical-pair dynamics.
Extract — continue reading at the source.
