10.1021/bi400561e.s001
Pascal Lanciano
Pascal
Lanciano
Bahia Khalfaoui-Hassani
Bahia
Khalfaoui-Hassani
Nur Selamoglu
Nur
Selamoglu
Fevzi Daldal
Fevzi
Daldal
Intermonomer Electron Transfer between the <i>b</i> Hemes of Heterodimeric Cytochrome <i>bc</i><sub>1</sub>
American Chemical Society
2016
bL hemes
Rhodobacter capsulatus
intermonomer electron transfer
heterodimeric Q cycle model
Intermonomer Electron Transfer
b Hemes
epitope tags
photosynthetic energy transduction pathways
photosynthetic growth
DOI
ATP
b heme cofactors
mass spectrometry analyses
dimeric cytochrome bc 1
heterodimeric cytochrome bc 1 variants
cytochrome bc 1.
c redox kinetics
proton gradient
heterodimeric variant
homodimeric organization
cytochrome bc 1 show
cytochrome b
cytochrome b subunits
2016-02-18 15:38:40
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Intermonomer_Electron_Transfer_between_the_i_b_i_Hemes_of_Heterodimeric_Cytochrome_i_bc_i_sub_1_sub_/2366386
The
ubihydroquinone:cytochrome <i>c</i> oxidoreductase,
or cytochrome <i>bc</i><sub>1</sub>, is a central component
of respiratory and photosynthetic energy transduction pathways in
many organisms. It contributes to the generation of membrane potential
and proton gradient used for cellular energy (ATP) production. The
three-dimensional structures of cytochrome <i>bc</i><sub>1</sub> show a homodimeric organization of its three catalytic subunits.
The unusual architecture revived the issue of whether the monomers
operate independently or function cooperatively during the catalytic
cycle of the enzyme. In recent years, different genetic approaches
allowed the successful production of heterodimeric cytochrome <i>bc</i><sub>1</sub> variants and evidenced the occurrence of
intermonomer electron transfer between the monomers of this enzyme.
Here we used a version of the “two-plasmid” genetic
system, also described in the preceding paper (DOI:
10.1021/bi400560p), to study a new heterodimeric mutant variant
of cytochrome <i>bc</i><sub>1</sub>. The strain producing
this heterodimeric variant sustained photosynthetic growth of <i>Rhodobacter capsulatus</i> and yielded an active heterodimer.
Interestingly, kinetic data showed equilibration of electrons among
the four <i>b</i> heme cofactors of the heterodimer, via
“reverse” intermonomer electron transfer between the <i>b</i><sub>L</sub> hemes. Both inactive homodimeric and active
heterodimeric cytochrome <i>bc</i><sub>1</sub> variants
were purified to homogeneity from the same cells, and purified samples
were subjected to mass spectrometry analyses. The data unequivocally
supported the idea that the cytochrome <i>b</i> subunits
carried the expected mutations and their associated epitope tags.
Implications of these findings on our interpretation of light-activated
transient cytochrome <i>b</i> and <i>c</i> redox
kinetics and the mechanism of function of a dimeric cytochrome <i>bc</i><sub>1</sub> are discussed with respect to the previously
proposed heterodimeric Q cycle model.