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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.

Author information

1
Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892.
2
Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078.
3
Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892 xiad@mail.nih.gov.

Abstract

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.

KEYWORDS:

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

PMID:
31182483
PMCID:
PMC6690702
[Available on 2020-08-09]
DOI:
10.1074/jbc.RA119.008381

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