Regensburg 2010 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 29: Biomolecular Spectroscopy

BP 29.9: Vortrag

Donnerstag, 25. März 2010, 16:45–17:00, H45

Photocycle Dynamics of the E149A Mutant of Cryptochrome 3 from Arabidopsis thaliana — Peyman Zirak¹, •Alfons Penzkofer¹, Judit Moldt², Richard Pokorny², Alfred Batschauer², and Lars-Oliver Essen³ — ¹Institut II - Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg — ²Fachbereich Biologie, Pflanzenphysiologie/Photobiologie, Philipps-Universität, Karl-von-Frisch-Str. 8, 35032 Marburg — ³Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str., 35032 Marburg

The E149A mutant of the cryDASH member cryptochrome 3 (cry3) from Arabidopsis thaliana was characterized in vitro by absorption and emission spectroscopy. The mutant protein non-covalently binds the cofactor flavin adenine dinucleotide (FAD), but not the second cofactor 5,10-methenyl-tetrahydrofolate (MTHF). Thus, the photo-dynamics caused by FAD is accessible without the intervening coupling with MTHF. In dark adapted cry3-E149A, FAD is present in the oxidized form (FAD_ox), semiquinone form (FADH^.), and anionic hydroquinone form (FAD_redH⁻). Blue-light photo-excitation of previously unexposed cry3-E149A transfers FAD_ox to the anionic semiquinone form (FAD^.−) with a quantum efficiency of 0.02 and a back recovery time of 10 s (photocycle I). Prolonged photo-excitation leads to an irreversible protein re-conformation leading to a change in the photo-cycle dynamics with photo-conversion of FAD_ox to FADH^. (efficiency 0.00032), of FADH^. to FAD_redH⁻ (efficiency 0.016), and thermal back equilibration in the dark on a minute timescale (photocycle II).