Ultrafast Oxidation of a Tyrosine by Proton-Coupled Electron Transfer Promotes Light Activation of an Animal-like Cryptochrome.
J Am Chem Soc
; 141(34): 13394-13409, 2019 08 28.
Article
in En
| MEDLINE
| ID: mdl-31368699
ABSTRACT
The animal-like cryptochrome of Chlamydomonas reinhardtii (CraCRY) is a recently discovered photoreceptor that controls the transcriptional profile and sexual life cycle of this alga by both blue and red light. CraCRY has the uncommon feature of efficient formation and longevity of the semireduced neutral form of its FAD cofactor upon blue light illumination. Tyrosine Y373 plays a crucial role by elongating , as fourth member, the electron transfer (ET) chain found in most other cryptochromes and DNA photolyases, which comprises a conserved tryptophan triad. Here, we report the full mechanism of light-induced FADH⢠formation in CraCRY using transient absorption spectroscopy from hundreds of femtoseconds to seconds. Electron transfer starts from ultrafast reduction of excited FAD to FADâ¢- by the proximal tryptophan (0.4 ps) and is followed by delocalized migration of the produced WHâ¢+ radical along the tryptophan triad (â¼4 and â¼50 ps). Oxidation of Y373 by coupled ET to WHâ¢+ and deprotonation then proceeds in â¼800 ps, without any significant kinetic isotope effect, nor a pH effect between pH 6.5 and 9.0. The FADâ¢-/Y373⢠pair is formed with high quantum yield (â¼60%); its intrinsic decay by recombination is slow (â¼50 ms), favoring reduction of Y373⢠by extrinsic agents and protonation of FADâ¢- to form the long-lived, red-light absorbing FADH⢠species. Possible mechanisms of tyrosine oxidation by ultrafast proton-coupled ET in CraCRY, a process about 40 times faster than the archetypal tyrosine-Z oxidation in photosystem II, are discussed in detail.
Full text:
1
Database:
MEDLINE
Main subject:
Plant Proteins
/
Tyrosine
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Chlamydomonas reinhardtii
/
Cryptochromes
Language:
En
Year:
2019
Type:
Article