Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 7, Issue 17, Pages 3472-3476Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.6b01484
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- NWO through VICI grant
- Middelgroot investment grant
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Light-triggered reactions of biological photoreceptors have gained immense attention for their role as molecular switches in their native organisms and for optogenetic application. The light, oxygen, and voltage 2 (LOV2) sensing domain of plant phototropin binds a C-terminal J alpha helix that is docked on a beta-sheet and unfolds upon light absorption by the flavin mononucleotide (FMN) chromophore. In this work, the signal transduction pathway of LOV2 from Avena sativa was investigated using time-resolved infrared spectroscopy from picoseconds to microseconds. In D2O buffer, FMN singlet-to-triplet conversion occurs in 2 ns and formation of the covalent cysteinyl-FMN adduct in 10 mu s. We observe a two-step unfolding of the J alpha helix: The first phase occurs concomitantly with Cys-FMN covalent adduct formation in 10 mu s, along with hydrogen-bond rupture of the FMN C4=O with Gln-513, motion of the beta-sheet, and an additional helical element. The second phase occurs in approximately 240 mu s. The final spectrum at 500 mu s is essentially identical to the steadystate light-minus-dark Fourier transform infrared spectrum, indicating that J alpha helix unfolding is complete on that time scale.
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