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Peripheral Methionine Residues Impact Flavin Photoreduction and Protonation in an Engineered LOV Domain Light Sensor
Estella F Yee1, Sabine Oldemeyer2, Elena Böhm2
1Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States.
Biochemistry
|March 31, 2021
Summary
Flavoprotein light sensors use proton-coupled electron transfer for signaling. Methionine and tyrosine residues in VVD-III protein control flavin photoreduction, favoring either anionic (ASQ) or neutral semiquinone (NSQ) formation based on protein environment.
Area of Science:
- Biochemistry
- Photobiology
- Protein Science
Background:
- Proton-coupled electron transfer (PCET) is vital for sensory phototransduction.
- Flavoprotein light sensors utilize flavin excited-state quenching for signal transmission.
- Understanding factors governing flavin photoreduction products (anionic semiquinone, ASQ vs. neutral semiquinone, NSQ) is crucial.
Purpose of the Study:
- To investigate the mechanism of flavin photoreduction and protonation in the LOV domain protein VVD-III.
- To elucidate the roles of specific amino acid residues in controlling the outcome of flavin photoreduction.
Main Methods:
- Utilized a modified VVD protein (VVD-III) lacking adduct-forming Cys.
- Employed site-directed mutagenesis, kinetic measurements, fluorescence quantum yield analysis, FTIR difference spectroscopy, and molecular dynamics simulations.
Main Results:
- Tyrosine residues promote charge recombination, limiting sustained flavin reduction.
- Methionine residues facilitate radical propagation, quenching, and gate solvent access for protonation.
- Replacing methionine with leucine favors ASQ formation and reduces oxidant sensitivity.
- Increasing hydrophilicity via glutamine substitution promotes NSQ formation and diminishes redox environment influence.
Conclusions:
- Flavin photoreactivity in VVD-III is governed by electron donors, internal quenching, and coupled proton transfer.
- Protein conformation, dynamics, and solvent accessibility critically influence PCET reactions and photoreductive outcomes.
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