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Coupled Methyl Group Rotation in FMN Radicals Revealed by Selective Deuterium Labeling
journal contribution
posted on 2020-02-20, 22:43 authored by Richard Brosi, Boris Illarionov, Lorenz Heidinger, Ryu-Ryun Kim, Markus Fischer, Stefan Weber, Adelbert Bacher, Robert Bittl, Erik SchleicherFlavin
semiquinones are common intermediate redox states in flavoproteins,
and thus, knowledge of their electronic structure is essential for
fully understanding their chemistry and chemical versatility. In this
contribution, we use a combination of high-field electron nuclear
double resonance spectroscopy and selective deuterium labeling of
flavin mononucleotide (FMN) with subsequent incorporation as cofactor
into a variant Avena sativa LOV domain
to extract missing traits of the electronic structure of a protein-bound
FMN radical. From these experiments, precise values of small proton
hyperfine and deuterium nuclear quadrupole couplings could be extracted.
Specifically, isotropic hyperfine couplings of −3.34, −0.11,
and +0.91 MHz were obtained for the protons H(6), H(9), and H(7α),
respectively. These values are discussed in the light of specific
protein–cofactor interactions. Furthermore, the temperature
behavior of the H(7α) methyl-group rotation elicited by its
energy landscape was analyzed in greater detail. Pronounced interplay
between the two methyl groups at C(7) and C(8) of FMN could be revealed.
Most strikingly, this rotational behavior could be modulated by selective
deuterium editing.
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redox statesFMN Radicals Revealedquadrupole couplingshigh-field electronFlavin semiquinonestemperature behaviorMethyl Group Rotationmethyl groupsprotonresonance spectroscopyflavin mononucleotidevariant Avena sativa LOV domainSelective DeuteriumPronounced interplaychemical versatilitydeuterium editingenergy landscape
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