2 research outputs found
Primary Photochemistry of the Dark- and Light-Adapted States of the YtvA Protein from <i>Bacillus subtilis</i>
The
primary (100 fs to 10 ns) and secondary (10 ns to 100 μs)
photodynamics in the type II light–oxygen–voltage (LOV)
domain from the blue light YtvA photoreceptor extracted from <i>Bacillus subtilis</i> were explored with transient absorption
spectroscopy. The photodynamics of full-length YtvA were characterized
after femtosecond 400 nm excitation of both the dark-adapted D<sub>447</sub> state and the light-adapted S<sub>390</sub> state. The
S<sub>390</sub> state relaxes on a 43 min time scale at room temperature
back into D<sub>447</sub>, which is weakly accelerated by the introduction
of imidazole. This is ascribed to an obstructed cavity in YtvA that
hinders access to the embedded FMN chromophore and is more open in
type I LOV domains. The primary photochemistry of dark-adapted YtvA
is qualitatively similar to that of the type I LOV domains, including
AsLOV2 from <i>Avena sativa</i>, but exhibits an appreciably
higher (60% greater) terminal triplet yield, estimated near the maximal
Φ<sub>ISC</sub> value of ≈78%; the other 22% decays via
non-triplet-generating fluorescence. The subsequent secondary dynamics
are inhomogeneous, with three triplet populations co-evolving: the
faster-decaying <sup>I</sup>T* population (38% occupancy) with a 200
ns decay time is nonproductive in generating the S<sub>390</sub> adduct
state, a slower <sup>II</sup>T* population (57% occupancy) exhibits
a high yield (Φ<sub>adduct</sub> ≈ 100%) in generating
S<sub>390</sub> and a third (5%) <sup>III</sup>T*population persists
(>100 μs) with unresolved photoactivity. The ultrafast photoswitching
dynamics of the S<sub>390</sub> state appreciably differ from those
previously resolved for the type I AcLOV2 domain from <i>Adiantum
capillus-veneris</i> [Kennis, J. T., et al. (2004) <i>J.
Am. Chem. Soc. 126</i>, 4512], with a low-yield dissociation
(Φ<sub>dis</sub> ≈ 2.5%) reaction, which is due to an
ultrafast recombination reaction, following photodissociation, and
is absent in AcLOV2, which results in the increased photoswitching
activity of the latter domain
Subpicosecond Excited-State Proton Transfer Preceding Isomerization During the Photorecovery of Photoactive Yellow Protein
The ultrafast excited-state dynamics underlying the receptor state photorecovery is resolved in the M100A mutant of the photoactive yellow protein (PYP) from Halorhodospira halophila. The M100A PYP mutant, with its distinctly slower photocycle than wt PYP, allows isolation of the pB signaling state for study of the photodynamics of the protonated chromophore <i>cis-p</i>-coumaric acid. Transient absorption signals indicate a subpicosecond excited-state proton-transfer reaction in the pB state that results in chromophore deprotonation prior to the cis−trans isomerization required in the photorecovery dynamics of the pG state. Two terminal photoproducts are observed, a blue-absorbing species presumed to be deprotonated <i>trans-p</i>-coumaric acid and an ultraviolet-absorbing protonated photoproduct. These two photoproducts are hypothesized to originate from an equilibrium of open and closed folded forms of the signaling state, I<sub>2</sub> and I<sub>2</sub>′