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LABORATOIRE D'ELECTROCHIMIE MOLECULAIREUniversité Paris 7 – Denis Diderot


Unité Mixte de Recherche CNRS / Paris 7 (7591) /

Séminaire du vendredi 15 décembre 2006

14h30, Salle 506, couloir 33-34 5ème étage

Electron transfer and proton dynamics in DNA photolyase: hopping along the FAD-Trp-Trp-Trp chain

Klaus Brettel

Service de Bioénergétique, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France

Abstract

DNA photolyase is a flavoprotein that catalyzes light-driven repair of major UV-induced DNA lesions (pyrimidine dimers). The photorepair reaction is presumably initiated by electron transfer from the excited state of the fully reduced FAD cofactor to the pyrimidine dimer. Another photoreaction of photolyase, named photoactivation, serves to re-establish the fully reduced form of the FAD cofactor once it has become oxidized to its semi-reduced form, the neutral radical FADH° that is typically found in isolated photolyase.

The presentation will focus on the reaction mechanism of photoactivation in E. coli photolyase, studied by fast and ultrafast transient absorption spectroscopy. Upon excitation, FADH° oxidizes the tryptophan residue W306 that is ~15Å apart and close to the surface of the protein so that it is readily re-reduced by extrinsic reductants. Evidence will be presented that

(1)oxidation of W306 occurs in two kinetically well separated steps: electron abstraction in <10 ns and proton release to bulk water in ~200 ns.

(2)

(3)Electron transfer from W306 to photoexcited FADH° is a three-step hopping process that involves two more tryptophan residues, W382 and W359, that bridge the distance between the flavin and W306. The first electron transfer step (from W382 to FADH°*) occurs in ~30 ps.

Part of the work has been reviewed by Martin Byrdin, Valérie Sartor, André P.M. Eker, Marten H. Vos, Corinne Aubert, Klaus Brettel & Paul Mathis in Biochim. Biophys. Acta1655, 64-70 (2004).

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