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J Biol Chem. 2019 Aug 9;294(32):12007-12019. doi: 10.1074/jbc.RA119.008381. Epub 2019 Jun 10.

Crystal structure of bacterial cytochrome bc 1 in complex with azoxystrobin reveals a conformational switch of the Rieske iron-sulfur protein subunit.

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Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892.
Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078.
Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892


Cytochrome bc 1 complexes (cyt bc 1), also known as complex III in mitochondria, are components of the cellular respiratory chain and of the photosynthetic apparatus of non-oxygenic photosynthetic bacteria. They catalyze electron transfer (ET) from ubiquinol to cytochrome c and concomitantly translocate protons across the membrane, contributing to the cross-membrane potential essential for a myriad of cellular activities. This ET-coupled proton translocation reaction requires a gating mechanism that ensures bifurcated electron flow. Here, we report the observation of the Rieske iron-sulfur protein (ISP) in a mobile state, as revealed by the crystal structure of cyt bc 1 from the photosynthetic bacterium Rhodobacter sphaeroides in complex with the fungicide azoxystrobin. Unlike cyt bc 1 inhibitors stigmatellin and famoxadone that immobilize the ISP, azoxystrobin causes the ISP-ED to separate from the cyt b subunit and to remain in a mobile state. Analysis of anomalous scattering signals from the iron-sulfur cluster of the ISP suggests the existence of a trajectory for electron delivery. This work supports and solidifies the hypothesis that the bimodal conformation switch of the ISP provides a gating mechanism for bifurcated ET, which is essential to the Q-cycle mechanism of cyt bc 1 function.


X-ray crystallography; conformation switch; conformational change; cytochrome; cytochrome bc1; electron transfer; electron transfer mechanism; respiratory chain; respiratory inhibitors

[Available on 2020-08-09]

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