Delocalized hole transport coupled to sub-ns tryptophanyl deprotonation promotes photoreduction of class II photolyases - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Physical Chemistry Chemical Physics Année : 2018

Delocalized hole transport coupled to sub-ns tryptophanyl deprotonation promotes photoreduction of class II photolyases

Résumé

Class II photolyases utilize for the photoreduction of their flavin cofactor (FAD) a completely different tryptophan triad than most other photolyases and cryptochromes. To counter sped-up back electron transfer, they evolved an unusually fast deprotonation of the distal tryptophanyl radical cation (WH •+) that is produced after excitation of the flavin. We studied the 2 primary aspects of oxidized FAD photoreduction by ultrafast transient absorption spectroscopy, using the class II photolyase from Methanosarcina mazei. With a time constant of 9.2 ps, the initial reduction step of the excited flavin by the proximal W 381 tryptophan proceeds almost twentyfold slower than in other photolyases carrying oxidized FAD, most likely because of the larger distance between the flavin and the proximal tryptophan. The thus formed W 381 H •+ radical is tracked by transient anisotropy measurements to migrate in 29 ps with delocalization over several members of the tryptophan triad. This 29-ps phase also includes the decay of a small fraction of excited flavin, reacting on a slower timescale, and a partial recombination of the FAD •-/WH •+ radical pair. A final kinetic phase in 230 ps is assigned to the deprotonation of W 388 H •+ that occurs in competition with partial charge recombination. Interestingly, we show by comparison with the Y345F mutant that this last phase additionally involves oxidation of the Y 345 phenolic group by W 388 H •+ , producing a small amount of neutral tyrosyl radical (YO •). The rate of this electron transfer step is about six orders of magnitude faster than the corresponding oxidation of Y 345 by the deprotonated W 388 • radical. Unlike conventional photolyases, where the electron hole accumulates on the distal tryptophan before the much slower tryptophanyl deprotonation, our data show that delocalized hole transport is concomitantly concluded by ultrafast deprotonation of W 388 H •+.
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Dates et versions

hal-01913266 , version 1 (24-01-2019)

Identifiants

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Fabien Lacombat, Agathe Espagne, Nadia Dozova, Pascal Plaza, Elisabeth Ignatz, et al.. Delocalized hole transport coupled to sub-ns tryptophanyl deprotonation promotes photoreduction of class II photolyases. Physical Chemistry Chemical Physics, 2018, 20 (39), pp.25446 - 25457. ⟨10.1039/c8cp04548h⟩. ⟨hal-01913266⟩
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