1 research outputs found
Unfolding of the C‑Terminal Jα Helix in the LOV2 Photoreceptor Domain Observed by Time-Resolved Vibrational Spectroscopy
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
Jα helix that is docked on a β-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 D<sub>2</sub>O buffer, FMN singlet-to-triplet conversion occurs in 2 ns and formation
of the covalent cysteinyl-FMN adduct in 10 μs. We observe a
two-step unfolding of the Jα helix: The first phase occurs concomitantly
with Cys-FMN covalent adduct formation in 10 μs, along with
hydrogen-bond rupture of the FMN C4î—»O with Gln-513, motion
of the β-sheet, and an additional helical element. The second
phase occurs in approximately 240 μs. The final spectrum at
500 μs is essentially identical to the steady-state light-minus-dark
Fourier transform infrared spectrum, indicating that Jα helix
unfolding is complete on that time scale