Abstract
Electronic connection between Qo and Qi quinone catalytic sites of dimeric cytochrome bc1 is a central feature of the energy-conserving Q cycle. While both the intra- and inter-monomer electron transfers were shown to connect the sites in the enzyme, mechanistic and physiological significance of the latter remains unclear. Here, using a series of mutated hybrid cytochrome bc1-like complexes, we show that inter-monomer electron transfer robustly sustains the function of the enzyme in vivo, even when the two subunits in a dimer come from different species. This indicates that minimal requirement for bioenergetic efficiency is to provide a chain of cofactors for uncompromised electron flux between the catalytic sites, while the details of protein scaffold are secondary.
Highlights
Cytochrome bc1 is a multi-subunit enzyme which transfers electrons between quinone molecules and cytochrome c and couples this electron transfer to proton translocation across the membrane
Photoheterotrophic growth of R. capsulatus requires obligatory presence of the functional cytochrome bc1, the most straightforward way to verify in vivo functionality of specific mutant derivatives of this complex is to test the capability of the mutant cells to grow under the photoheterotrophic conditions [20]
We used this approach in combination with the asymmetric mutagenesis to assess physiological relevance of the inter-monomer electron transfer in cytochrome bc1
Summary
Cytochrome bc (ubihydroquinone:cytochrome c oxidoreductase or mitochondrial complex III) is a multi-subunit enzyme which transfers electrons between quinone molecules and cytochrome c and couples this electron transfer to proton translocation across the membrane. This way cytochrome bc contributes to generation of the protonmotive force used for cellular ATP production [1]. The Qo and Qi sites are connected by a chain composed of two hemes (heme bL and heme bH), while a chain composed of FeS and heme c1 connects the Qo site with cytochrome c pool. The scheme shows that cytochrome bc is a homodimer
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More From: Biochemical and Biophysical Research Communications
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