title: Variable electron transfer pathways in an amphibian cryptochrome: tryptophan versus tyrosine-based radical pairs.
abstract: Electron transfer reactions play vital roles in many biological processes. Very often the transfer of charge(s) proceeds stepwise over large distances involving several amino acid residues. By using time-resolved electron paramagnetic resonance and optical spectroscopy, we have studied the mechanism of light-induced reduction of the FAD cofactor of cryptochrome/photolyase family proteins. In this study, we demonstrate that electron abstraction from a nearby amino acid by the excited FAD triggers further electron transfer steps even if the conserved chain of three tryptophans, known to be an effective electron transfer pathway in these proteins, is blocked. Furthermore, we were able to characterize this secondary electron transfer pathway and identify the amino acid partner of the resulting flavin-amino acid radical pair as a tyrosine located at the protein surface. This alternative electron transfer pathway could explain why interrupting the conserved tryptophan triad does not necessarily alter photoreactions of cryptochromes in vivo. Taken together, our results demonstrate that light-induced electron transfer is a robust property of cryptochromes and more intricate than commonly anticipated.
authors: Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom.
authors: Till
authors: T
authors: Biskup
authors: Bernd
authors: B
authors: Paulus
authors: Asako
authors: A
authors: Okafuji
authors: Kenichi
authors: K
authors: Hitomi
authors: Elizabeth D
authors: ED
authors: Getzoff
authors: Stefan
authors: S
authors: Weber
authors: Erik
authors: E
authors: Schleicher
mesh_terms: D000663:Amphibians; D000818:Animals; D056931:Cryptochromes / Q000737:chemistry*; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport / Q000235:genetics*; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D008968:Molecular Conformation; D055095:Optics and Photonics / Q000379:methods; D010777:Photochemistry / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D056931:Cryptochromes; D005182:Flavin-Adenine Dinucleotide; D014443:Tyrosine; D014364:Tryptophan; D004255:Deoxyribodipyrimidine Photo-Lyase