1
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Zhan J, Zeher A, Huang R, Tang WK, Jenkins LM, Xia D. Conformations of Bcs1L undergoing ATP hydrolysis suggest a concerted translocation mechanism for folded iron-sulfur protein substrate. Nat Commun 2024; 15:4655. [PMID: 38821922 PMCID: PMC11143374 DOI: 10.1038/s41467-024-49029-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Accepted: 05/20/2024] [Indexed: 06/02/2024] Open
Abstract
The human AAA-ATPase Bcs1L translocates the fully assembled Rieske iron-sulfur protein (ISP) precursor across the mitochondrial inner membrane, enabling respiratory Complex III assembly. Exactly how the folded substrate is bound to and released from Bcs1L has been unclear, and there has been ongoing debate as to whether subunits of Bcs1L act in sequence or in unison hydrolyzing ATP when moving the protein cargo. Here, we captured Bcs1L conformations by cryo-EM during active ATP hydrolysis in the presence or absence of ISP substrate. In contrast to the threading mechanism widely employed by AAA proteins in substrate translocation, subunits of Bcs1L alternate uniformly between ATP and ADP conformations without detectable intermediates that have different, co-existing nucleotide states, indicating that the subunits act in concert. We further show that the ISP can be trapped by Bcs1 when its subunits are all in the ADP-bound state, which we propose to be released in the apo form.
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Affiliation(s)
- Jingyu Zhan
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Allison Zeher
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
- NIH Intramural Cryo-EM Consortium (NICE), Bethesda, MD, USA
| | - Rick Huang
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
- NIH Intramural Cryo-EM Consortium (NICE), Bethesda, MD, USA
| | - Wai Kwan Tang
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Lisa M Jenkins
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Di Xia
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA.
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2
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Havens J, Su T, Wang Q, Yu CA, Yu L, Durham B, Millett F. Photoinduced electron transfer in cytochrome bc 1: Dynamics of rotation of the Iron-sulfur protein during bifurcated electron transfer from ubiquinol to cytochrome c 1 and cytochrome b L. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2023; 1864:148957. [PMID: 36709837 DOI: 10.1016/j.bbabio.2023.148957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2022] [Revised: 01/12/2023] [Accepted: 01/20/2023] [Indexed: 01/27/2023]
Abstract
The electron transfer reactions within wild-type Rhodobacter sphaeroides cytochrome bc1 (cyt bc1) were studied using a binuclear ruthenium complex to rapidly photooxidize cyt c1. When cyt c1, the iron‑sulfur center Fe2S2, and cyt bH were reduced before the reaction, photooxidation of cyt c1 led to electron transfer from Fe2S2 to cyt c1 with a rate constant of ka = 80,000 s-1, followed by bifurcated reduction of both Fe2S2 and cyt bL by QH2 in the Qo site with a rate constant of k2 = 3000 s-1. The resulting Q then traveled from the Qo site to the Qi site and oxidized one equivalent each of cyt bL and cyt bH with a rate constant of k3 = 340 s-1. The rate constant ka was decreased in a nonlinear fashion by a factor of 53 as the viscosity was increased to 13.7. A mechanism that is consistent with the effect of viscosity involves rotational diffusion of the iron‑sulfur protein from the b state with reduced Fe2S2 close to cyt bL to one or more intermediate states, followed by rotation to the final c1 state with Fe2S2 close to cyt c1, and rapid electron transfer to cyt c1.
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Affiliation(s)
- Jeffrey Havens
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, United States of America; Vaccines and Therapeutics Division, Chemical and Biological Technologies, Defense Threat Reduction Agency, Fort Belvoir, VA 22060, United States of America
| | - Ting Su
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, United States of America; ABclonal Technology Woburn, MA 01801, United States of America
| | - Qiyu Wang
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, United States of America; Vesigen Therapeutics Cambridge, MA 02139, United States of America
| | - Chang-An Yu
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, United States of America
| | - Linda Yu
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, United States of America
| | - Bill Durham
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, United States of America
| | - Francis Millett
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, United States of America.
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3
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Sindhu T, Debnath P. Cytochrome bc1-aa3 oxidase supercomplex as emerging and potential drug target against tuberculosis. Curr Mol Pharmacol 2021; 15:380-392. [PMID: 34602044 DOI: 10.2174/1874467214666210928152512] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 03/26/2021] [Accepted: 06/06/2021] [Indexed: 11/22/2022]
Abstract
The cytochrome bc1-aa3 supercomplex plays an essential role in the cellular respiratory system of Mycobacterium Tuberculosis. It transfers electrons from menaquinol to cytochrome aa3 (Complex IV) via cytochrome bc1 (Complex III), which reduces the oxygen. The electron transfer from a variety of donors into oxygen through the respiratory electron transport chain is essential to pump protons across the membrane creating an electrochemical transmembrane gradient (proton motive force, PMF) that regulates the synthesis of ATP via the oxidative phosphorylation process. Cytochrome bc1-aa3 supercomplex in M. tuberculosis is, therefore, a major drug target for antibiotic action. In recent years, several respiratory chain components have been targeted for developing new candidate drugs, illustrating the therapeutic potential of obstructing energy conversion of M. tuberculosis. The recently available cryo-EM structure of mycobacterial cytochrome bc1-aa3 supercomplex with open and closed conformations has opened new avenues for understanding its structure and function for developing more effective, new therapeutics against pulmonary tuberculosis. In this review, we discuss the role and function of several components, subunits, and drug targeting elements of the supercomplex cytochrome bc1-aa3, and its potential inhibitors in detail.
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Affiliation(s)
- Thangaraj Sindhu
- Department of Computational and Data Sciences, Indian Institute of Science, Bangalore, Karnataka. India
| | - Pal Debnath
- Department of Computational and Data Sciences, Indian Institute of Science, Bangalore, Karnataka. India
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4
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Sarewicz M, Pintscher S, Pietras R, Borek A, Bujnowicz Ł, Hanke G, Cramer WA, Finazzi G, Osyczka A. Catalytic Reactions and Energy Conservation in the Cytochrome bc1 and b6f Complexes of Energy-Transducing Membranes. Chem Rev 2021; 121:2020-2108. [PMID: 33464892 PMCID: PMC7908018 DOI: 10.1021/acs.chemrev.0c00712] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Indexed: 12/16/2022]
Abstract
This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome bc1 and b6f (Cytbc1/b6f) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes c or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cytsbc1/b6f share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cytbc1/b6f, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cytsbc1/b6f. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.
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Affiliation(s)
- Marcin Sarewicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Sebastian Pintscher
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Rafał Pietras
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Arkadiusz Borek
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Łukasz Bujnowicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Guy Hanke
- School
of Biological and Chemical Sciences, Queen
Mary University of London, London E1 4NS, U.K.
| | - William A. Cramer
- Department
of Biological Sciences, Purdue University, West Lafayette, Indiana 47907 United States
| | - Giovanni Finazzi
- Laboratoire
de Physiologie Cellulaire et Végétale, Université Grenoble Alpes, Centre National Recherche Scientifique,
Commissariat Energie Atomique et Energies Alternatives, Institut National
Recherche l’agriculture, l’alimentation et l’environnement, 38054 Grenoble Cedex 9, France
| | - Artur Osyczka
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
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5
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Xia D. Structural snapshots of the cellular folded protein translocation machinery Bcs1. FEBS J 2020; 288:2870-2883. [PMID: 32979284 PMCID: PMC7994207 DOI: 10.1111/febs.15576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 09/05/2020] [Accepted: 09/22/2020] [Indexed: 11/29/2022]
Abstract
Proteins destined to various intra‐ and extra‐cellular locations must traverse membranes most frequently in an unfolded form. When the proteins being translocated need to remain in a folded state, specialized cellular transport machinery is used. One such machine is the membrane‐bound AAA protein Bcs1 (Bcs1), which assists the iron‐sulfur protein, an essential subunit of the respiratory Complex III, across the mitochondrial inner membrane. Recent structure determinations of mouse and yeast Bcs1 in three different nucleotide states reveal its homo‐heptameric association and at least two dramatically different conformations. The apo and ADP‐bound structures are similar, both containing a large substrate‐binding cavity accessible to the mitochondrial matrix space, which contracts by concerted motion of the ATPase domains upon ATP binding, suggesting that bound substrate could then be pushed across the membrane. ATP hydrolysis drives substrate release and resets Bcs1 conformation back to the apo/ADP form. These structures shed new light on the mechanism of folded protein translocation across a membrane, provide better understanding on the assembly process of the respiratory Complex III, and correlate clinical presentations of disease‐associated mutations with their locations in the 3D structure.
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Affiliation(s)
- Di Xia
- Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
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6
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Kokhan O, Marzolf DR. Detection and quantification of transition metal leaching in metal affinity chromatography with hydroxynaphthol blue. Anal Biochem 2019; 582:113347. [PMID: 31251926 DOI: 10.1016/j.ab.2019.113347] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Revised: 06/13/2019] [Accepted: 06/24/2019] [Indexed: 11/17/2022]
Abstract
The widespread use of immobilized metal-affinity chromatography (IMAC) for fast and efficient purification of recombinant proteins has brought potentially toxic transition elements into common laboratory usage. However, there are few studies on the leaching of metal from the affinity resin, such as nickel-nitrilotriacetic acid (Ni-NTA), with possible deleterious impact on the biological activity. This is of particular importance when reducing or chelating eluants stronger than imidazole are used. We present a detailed study of hydroxynaphthol blue (HNB) as an indicator of several divalent metal cations, but with emphasis on Ni2+, clarifying and correcting many errors and ambiguities in the older literature on this dye compound. The assay is simple and sensitive and many metals, notably Ni2+, Zn2+, Cu2+, Pb2+, Fe2+, Co2+, and Al3+, can be readily detected and quantified at concentrations down to 15-50 nM (1-5 ppb) at neutral pH and in most commonly used buffers using spectroscopic equipment available in typical biochemistry research labs. Using this method, we show that significant amounts of Ni2+ (up to 20 mM) are co-purified with a target protein (cytochrome bc1 complex) when histidine is used to elute from Ni-NTA resin.
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Affiliation(s)
- Oleksandr Kokhan
- Department of Chemistry and Biochemistry, James Madison University, 901 Carrier Drive, Harrisonburg, VA, 22807, USA.
| | - Daniel R Marzolf
- Department of Chemistry and Biochemistry, James Madison University, 901 Carrier Drive, Harrisonburg, VA, 22807, USA
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7
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Esser L, Zhou F, Yu CA, Xia D. Crystal structure of bacterial cytochrome bc 1 in complex with azoxystrobin reveals a conformational switch of the Rieske iron-sulfur protein subunit. J Biol Chem 2019; 294:12007-12019. [PMID: 31182483 DOI: 10.1074/jbc.ra119.008381] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 06/06/2019] [Indexed: 11/06/2022] Open
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.
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Affiliation(s)
- Lothar Esser
- Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Fei Zhou
- Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Chang-An Yu
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078
| | - Di Xia
- Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892.
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8
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Borek A, Ekiert R, Osyczka A. Functional flexibility of electron flow between quinol oxidation Q o site of cytochrome bc 1 and cytochrome c revealed by combinatory effects of mutations in cytochrome b, iron-sulfur protein and cytochrome c 1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1859:754-761. [PMID: 29705394 DOI: 10.1016/j.bbabio.2018.04.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2018] [Revised: 04/16/2018] [Accepted: 04/24/2018] [Indexed: 01/07/2023]
Abstract
Transfer of electron from quinol to cytochrome c is an integral part of catalytic cycle of cytochrome bc1. It is a multi-step reaction involving: i) electron transfer from quinol bound at the catalytic Qo site to the Rieske iron-sulfur ([2Fe-2S]) cluster, ii) large-scale movement of a domain containing [2Fe-2S] cluster (ISP-HD) towards cytochrome c1, iii) reduction of cytochrome c1 by reduced [2Fe-2S] cluster, iv) reduction of cytochrome c by cytochrome c1. In this work, to examine this multi-step reaction we introduced various types of barriers for electron transfer within the chain of [2Fe-2S] cluster, cytochrome c1 and cytochrome c. The barriers included: impediment in the motion of ISP-HD, uphill electron transfer from [2Fe-2S] cluster to heme c1 of cytochrome c1, and impediment in the catalytic quinol oxidation. The barriers were introduced separately or in various combinations and their effects on enzymatic activity of cytochrome bc1 were compared. This analysis revealed significant degree of functional flexibility allowing the cofactor chains to accommodate certain structural and/or redox potential changes without losing overall electron and proton transfers capabilities. In some cases inhibitory effects compensated one another to improve/restore the function. The results support an equilibrium model in which a random oscillation of ISP-HD between the Qo site and cytochrome c1 helps maintaining redox equilibrium between all cofactors of the chain. We propose a new concept in which independence of the dynamics of the Qo site substrate and the motion of ISP-HD is one of the elements supporting this equilibrium and also is a potential factor limiting the overall catalytic rate.
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Affiliation(s)
- Arkadiusz Borek
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Robert Ekiert
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Artur Osyczka
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland.
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9
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Qu Y, Dong F. New methods for determining proton pumping ability and electron transfer activity of the cytochrome bc1 complex. Acta Biochim Biophys Sin (Shanghai) 2015; 47:114-20. [PMID: 25543120 DOI: 10.1093/abbs/gmu126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
It is important to determine the electron transfer activity and proton pumping ability of the cytochrome bc1 complex for better understanding its structure and function. In this study, several methods for determining the electron transfer and proton pumping of the bc1 complex, including the traditional and the new methods, are presented and evaluated. For determining the proton pumping ability of the bc1 complex, the new stopped-flow method has a higher accuracy than the traditional pH meter method, and the new spectrophotometer method is more convenient than the traditional pH meter method. In measuring the electron transfer activity of the bc1 complex, the new stopped-flow method is more accurate and has a higher separating capacity than the traditional spectrophotometer method.
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Affiliation(s)
- Yuangang Qu
- College of Life Sciences, Linyi University, Linyi 276000, China Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater 74078, USA
| | - Fang Dong
- College of Life Sciences, Linyi University, Linyi 276000, China
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10
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Sarewicz M, Osyczka A. Electronic connection between the quinone and cytochrome C redox pools and its role in regulation of mitochondrial electron transport and redox signaling. Physiol Rev 2015; 95:219-43. [PMID: 25540143 PMCID: PMC4281590 DOI: 10.1152/physrev.00006.2014] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Mitochondrial respiration, an important bioenergetic process, relies on operation of four membranous enzymatic complexes linked functionally by mobile, freely diffusible elements: quinone molecules in the membrane and water-soluble cytochromes c in the intermembrane space. One of the mitochondrial complexes, complex III (cytochrome bc1 or ubiquinol:cytochrome c oxidoreductase), provides an electronic connection between these two diffusible redox pools linking in a fully reversible manner two-electron quinone oxidation/reduction with one-electron cytochrome c reduction/oxidation. Several features of this homodimeric enzyme implicate that in addition to its well-defined function of contributing to generation of proton-motive force, cytochrome bc1 may be a physiologically important point of regulation of electron flow acting as a sensor of the redox state of mitochondria that actively responds to changes in bioenergetic conditions. These features include the following: the opposing redox reactions at quinone catalytic sites located on the opposite sides of the membrane, the inter-monomer electronic connection that functionally links four quinone binding sites of a dimer into an H-shaped electron transfer system, as well as the potential to generate superoxide and release it to the intermembrane space where it can be engaged in redox signaling pathways. Here we highlight recent advances in understanding how cytochrome bc1 may accomplish this regulatory physiological function, what is known and remains unknown about catalytic and side reactions within the quinone binding sites and electron transfers through the cofactor chains connecting those sites with the substrate redox pools. We also discuss the developed molecular mechanisms in the context of physiology of mitochondria.
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Affiliation(s)
- Marcin Sarewicz
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Kraków, Poland
| | - Artur Osyczka
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Kraków, Poland
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11
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Xia D, Esser L, Tang WK, Zhou F, Zhou Y, Yu L, Yu CA. Structural analysis of cytochrome bc1 complexes: implications to the mechanism of function. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1827:1278-94. [PMID: 23201476 PMCID: PMC3593749 DOI: 10.1016/j.bbabio.2012.11.008] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 11/13/2012] [Accepted: 11/19/2012] [Indexed: 01/18/2023]
Abstract
The cytochrome bc1 complex (bc1) is the mid-segment of the cellular respiratory chain of mitochondria and many aerobic prokaryotic organisms; it is also part of the photosynthetic apparatus of non-oxygenic purple bacteria. The bc1 complex catalyzes the reaction of transferring electrons from the low potential substrate ubiquinol to high potential cytochrome c. Concomitantly, bc1 translocates protons across the membrane, contributing to the proton-motive force essential for a variety of cellular activities such as ATP synthesis. Structural investigations of bc1 have been exceedingly successful, yielding atomic resolution structures of bc1 from various organisms and trapped in different reaction intermediates. These structures have confirmed and unified results of decades of experiments and have contributed to our understanding of the mechanism of bc1 functions as well as its inactivation by respiratory inhibitors. This article is part of a Special Issue entitled: Respiratory complex III and related bc complexes.
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Affiliation(s)
- Di Xia
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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12
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Berry EA, De Bari H, Huang LS. Unanswered questions about the structure of cytochrome bc1 complexes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:1258-77. [PMID: 23624176 DOI: 10.1016/j.bbabio.2013.04.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Revised: 03/13/2013] [Accepted: 04/16/2013] [Indexed: 11/25/2022]
Abstract
X-ray crystal structures of bc1 complexes obtained over the last 15 years have provided a firm structural basis for our understanding of the complex. For the most part there is good agreement between structures from different species, different crystal forms, and with different inhibitors bound. In this review we focus on some of the remaining unexplained differences, either between the structures themselves or the interpretations of the structural observations. These include the structural basis for the motion of the Rieske iron-sulfur protein in response to inhibitors, a possible conformational change involving tyrosine132 of cytochrome (cyt) b, the presence of cis-peptides at the beginnings of transmembrane helices C, E, and H, the structural insight into the function of the so-called "Core proteins", different modelings of the retained signal peptide, orientation of the low-potential heme b, and chirality of the Met ligand to heme c1. This article is part of a Special Issue entitled: Respiratory complex III and related bc complexes.
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Affiliation(s)
- Edward A Berry
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA.
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13
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Millett F, Havens J, Rajagukguk S, Durham B. Design and use of photoactive ruthenium complexes to study electron transfer within cytochrome bc1 and from cytochrome bc1 to cytochrome c. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:1309-19. [PMID: 22985600 DOI: 10.1016/j.bbabio.2012.09.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Revised: 08/29/2012] [Accepted: 09/03/2012] [Indexed: 10/27/2022]
Abstract
The cytochrome bc1 complex (ubiquinone:cytochrome c oxidoreductase) is the central integral membrane protein in the mitochondrial respiratory chain as well as the electron-transfer chains of many respiratory and photosynthetic prokaryotes. Based on X-ray crystallographic studies of cytochrome bc1, a mechanism has been proposed in which the extrinsic domain of the iron-sulfur protein first binds to cytochrome b where it accepts an electron from ubiquinol in the Qo site, and then rotates by 57° to a position close to cytochrome c1 where it transfers an electron to cytochrome c1. This review describes the development of a ruthenium photooxidation technique to measure key electron transfer steps in cytochrome bc1, including rapid electron transfer from the iron-sulfur protein to cytochrome c1. It was discovered that this reaction is rate-limited by the rotational dynamics of the iron-sulfur protein rather than true electron transfer. A conformational linkage between the occupant of the Qo ubiquinol binding site and the rotational dynamics of the iron-sulfur protein was discovered which could play a role in the bifurcated oxidation of ubiquinol. A ruthenium photoexcitation method is also described for the measurement of electron transfer from cytochrome c1 to cytochrome c. This article is part of a Special Issue entitled: Respiratory Complex III and related bc complexes.
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Key Words
- 2,2′-bipyrazine
- 2,2′-bipyridine
- 2,2′:4′,4″:2″,2‴-quaterpyridine
- 2Fe2S
- 3,3′-bipyridazine
- 4,4′-dimethyl-2,2′-bipridine
- Cc
- CcO
- Cytochrome bc(1)
- Cytochrome c
- Electron transfer
- ISP
- JG144
- MOAS
- P(f)
- P(m)
- Q
- Q(i)
- Q(o)
- Q(o) site inhibitor which fixes ISP in b state
- Q(o) site inhibitor which promotes mobile state of ISP
- QH(2)
- R. sphaeroides
- Rhodobacter sphaeroides
- Rieske iron–sulfur center
- Ru(2)D
- Ruthenium
- S-3-anilino-5-methyl-5-(4,6-difluorophenyl)-1,3-oxazolidine-2,4-dione
- [Ru(bpy)(2)](2)qpy(4+)
- bpd
- bpy
- bpz
- cyt bc(1)
- cytochrome bc(1)
- cytochrome c
- cytochrome c oxidase
- dmb
- inside ubiquinone binding site
- iron–sulfur protein
- methoxyacrylate stilbene
- outside ubiquinol binding site
- qpy
- ubiquinol
- ubiquionone
- yCc
- yeast Cc
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Affiliation(s)
- Francis Millett
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
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14
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Yang WC, Li H, Wang F, Zhu XL, Yang GF. Rieske Iron-Sulfur Protein of the Cytochrome bc1 Complex: A Potential Target for Fungicide Discovery. Chembiochem 2012; 13:1542-51. [DOI: 10.1002/cbic.201200295] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2012] [Indexed: 01/17/2023]
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15
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Kallas T. Cytochrome b 6 f Complex at the Heart of Energy Transduction and Redox Signaling. PHOTOSYNTHESIS 2012. [DOI: 10.1007/978-94-007-1579-0_21] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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16
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Havens J, Castellani M, Kleinschroth T, Ludwig B, Durham B, Millett F. Photoinitiated electron transfer within the Paracoccus denitrificans cytochrome bc1 complex: mobility of the iron-sulfur protein is modulated by the occupant of the Q(o) site. Biochemistry 2011; 50:10462-72. [PMID: 22026826 DOI: 10.1021/bi200453r] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Domain rotation of the Rieske iron-sulfur protein (ISP) between the cytochrome (cyt) b and cyt c(1) redox centers plays a key role in the mechanism of the cyt bc(1) complex. Electron transfer within the cyt bc(1) complex of Paracoccus denitrificans was studied using a ruthenium dimer to rapidly photo-oxidize cyt c(1) within 1 μs and initiate the reaction. In the absence of any added quinol or inhibitor of the bc(1) complex at pH 8.0, electron transfer from reduced ISP to cyt c(1) was biphasic with rate constants of k(1f) = 6300 ± 3000 s(-1)and k(1s) = 640 ± 300 s(-1) and amplitudes of 10 ± 3% and 16 ± 4% of the total amount of cyt c(1) photooxidized. Upon addition of any of the P(m) type inhibitors MOA-stilbene, myxothiazol, or azoxystrobin to cyt bc(1) in the absence of quinol, the total amplitude increased 2-fold, consistent with a decrease in redox potential of the ISP. In addition, the relative amplitude of the fast phase increased significantly, consistent with a change in the dynamics of the ISP domain rotation. In contrast, addition of the P(f) type inhibitors JG-144 and famoxadone decreased the rate constant k(1f) by 5-10-fold and increased the amplitude over 2-fold. Addition of quinol substrate in the absence of inhibitors led to a 2-fold increase in the amplitude of the k(1f) phase. The effect of QH(2) on the kinetics of electron transfer from reduced ISP to cyt c(1) was thus similar to that of the P(m) inhibitors and very different from that of the P(f) inhibitors. The current results indicate that the species occupying the Q(o) site has a significant conformational influence on the dynamics of the ISP domain rotation.
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Affiliation(s)
- Jeffrey Havens
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, United States
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17
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Gong L, Yang X, Zhang B, Zhong G, Hu M. Silencing of Rieske iron-sulfur protein using chemically synthesised siRNA as a potential biopesticide against Plutella xylostella. PEST MANAGEMENT SCIENCE 2011; 67:514-520. [PMID: 21472969 DOI: 10.1002/ps.2086] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 09/25/2010] [Accepted: 09/29/2010] [Indexed: 05/30/2023]
Abstract
BACKGROUND Extensive applications and frequent long-term use of pesticides can affect behavioural mechanisms and physiological and biochemical aspects of insects, leading to resistance. However, insect control strategies involving a different mode of action would be valuable for managing the emergence of insect resistance. In this context, the development of RNA interference technology has brought a turning point in the creation of new biopesticides. RESULTS Full-length cDNA of Rieske iron-sulfur protein (RISP) was cloned and characterised from Plutella xylostella L. Three siRNAs specific to RISP sequences were designed and chemically synthesised, and fed to P. xylostella larvae by coating cabbage leaves. This resulted in specific gene silencing of RISP, and consequently brought significant mortality of P. xylostella larvae compared with the control treatment. Silencing of RISP leads to significantly lower transcript levels of RISP compared with the control. In addition, the amount of ATP in the surviving larvae was lower than in the control. However, surviving larvae gradually recovered to normal transcript and protein levels. CONCLUSION This is the first demonstration of the potential use of chemically synthesised siRNA in the development of new biopesticides as a mitochondrial electron transport inhibitor.
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Affiliation(s)
- Liang Gong
- Key Laboratory of Pesticide and Chemical Biology, College of Natural Resources and Environment, South China Agricultural University, Guangzhou, China
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18
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Yin Y, Yang S, Yu L, Yu CA. Reaction mechanism of superoxide generation during ubiquinol oxidation by the cytochrome bc1 complex. J Biol Chem 2010; 285:17038-45. [PMID: 20371599 DOI: 10.1074/jbc.m110.104364] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In addition to its main functions of electron transfer and proton translocation, the cytochrome bc(1) complex (bc(1)) also catalyzes superoxide anion (O(2)(*)) generation upon oxidation of ubiquinol in the presence of molecular oxygen. The reaction mechanism of superoxide generation by bc(1) remains elusive. The maximum O(2)(*) generation activity is observed when the complex is inhibited by antimycin A or inactivated by heat treatment or proteinase K digestion. The fact that the cytochrome bc(1) complex with less structural integrity has higher O(2)(*)-generating activity encouraged us to speculate that O(2)(*) is generated inside the complex, perhaps in the hydrophobic environment of the Q(P) pocket through bifurcated oxidation of ubiquinol by transferring its two electrons to a high potential electron acceptor, iron-sulfur cluster, and a low potential heme b(L) or molecular oxygen. If this speculation is correct, then one should see more O(2)(*) generation upon oxidation of ubiquinol by a high potential oxidant, such as cytochrome c or ferricyanide, in the presence of phospholipid vesicles or detergent micelles than in the hydrophilic conditions, and this is indeed the case. The protein subunits, at least those surrounding the Q(P) pocket, may play a role either in preventing the release of O(2)(*) from its production site to aqueous environments or in preventing O(2) from getting access to the hydrophobic Q(P) pocket and might not directly participate in superoxide production.
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Affiliation(s)
- Ying Yin
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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19
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Cooley JW, Lee DW, Daldal F. Across membrane communication between the Q(o) and Q(i) active sites of cytochrome bc(1). Biochemistry 2009; 48:1888-99. [PMID: 19254042 DOI: 10.1021/bi802216h] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ubihydroquinone:cytochrome c oxidoreductase (cyt bc(1)) contains two catalytically active domains, termed the hydroquinone oxidation (Q(o)) and quinone reduction (Q(i)) sites, which are distant from each other by over 30 A. Previously, we have reported that binding of inhibitors to the Q(i) site on one (n) side of the energy-transducing membrane changes the local environment of the iron-sulfur (Fe/S) protein subunit residing in the Q(o) site on the other (p) side of the lipid bilayer [Cooley, J. W., Ohnishi, T., and Daldal, F. (2005) Biochemistry 44, 10520-10532]. These findings best fit a model whereby the Q(o) and Q(i) sites of the cyt bc(1) are actively coupled in spite of their distant locations. Because the Fe/S protein of the cyt bc(1) undergoes a large-scale (macro) domain movement during catalysis, we examined various macromobility-defective Fe/S subunit mutants to assess the role of this motion on the coupling of the active sites and also during the multiple turnovers of the enzyme. By monitoring the changing environments of the Fe/S protein [2Fe-2S] cluster upon addition of Q(i) site inhibitors in selected mutants, we found that the Q(o)-Q(i) site interactions manifest differently depending on the ability of the Fe/S protein to move between the cytochrome b and cytochrome c(1) subunits of the enzyme. In the presence of antimycin A, an immobile Fe/S protein mutant exhibited no changes in its EPR spectra. In contrast, mobility-restricted mutants showed striking alterations in the EPR line shapes and revealed two discrete subpopulations in respect to the [2Fe-2S] cluster environments at the Q(o) site. These findings led us to conclude that the mobility of the Fe/S protein is involved in its response to the occupancy of the Q(i) site by different molecules. We propose that the heterogeneity seen might reflect the distinct responses of the two Fe/S proteins at the Q(o) sites of the dimeric enzyme upon the occupancy of the Q(i) sites and discuss it in terms of the function of the dimeric cyt bc(1) during its multiple turnovers.
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Affiliation(s)
- Jason W Cooley
- Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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20
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Yu L, Yang S, Yin Y, Cen X, Zhou F, Xia D, Yu CA. Chapter 25 Analysis of electron transfer and superoxide generation in the cytochrome bc1 complex. Methods Enzymol 2009; 456:459-73. [PMID: 19348904 DOI: 10.1016/s0076-6879(08)04425-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
Abstract
During the electron transfer through the cytochrome bc(1) complex (ubiquinol-cytochrome c oxidoreductase or complex III), protons are translocated across the membrane, and production of superoxide anion radicals (O(2)(*-)) is observed. The bc(1) complex is purified from broken mitochondrial preparation prepared from frozen heart muscles by repeated detergent solubilization and salt fractionation. The electron transfer of the purified complex is determined spectrophotometrically. The activity depends on the choice of detergent, protein concentration, and ubiquinol derivatives used. The proton translocation activity of 2H(+)/e(-) is determined in the reconstituted bc(1)-PL vesicles. The O(2)(*-) production by bc(1) is determined by measuring the chemiluminescence of the 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazol[1,2-1]pyrazin-3-one hydrochloride (MCLA)-O(2)(*-) adduct during a single turnover of bc(1) complex, with the Applied Photophysics stopped-flow reaction analyzer SX.18MV, by leaving the excitation light source off and registering the light emission. Production of O(2)(*-) by bc(1) is in an inverse relationship to its electron transfer activity. Inactivation of the bc(1) complex by incubating at elevated temperature (37 degrees C) or by treatment with proteinase K results in an increase in O(2)(*-)-generating activity to the same level as that of the antimycin A-inhibited complex. These results suggest that the structural integrity of protein subunits is not required for O(2)(*-)-generating activity in the bc(1) complex.
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Affiliation(s)
- Linda Yu
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma, USA
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21
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Yin Y, Tso SC, Yu CA, Yu L. Effect of subunit IV on superoxide generation by Rhodobacter sphaeroides cytochrome bc(1) complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:913-9. [PMID: 19348783 DOI: 10.1016/j.bbabio.2009.03.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2008] [Revised: 03/30/2009] [Accepted: 03/30/2009] [Indexed: 10/20/2022]
Abstract
Previous studies indicate that the three-subunit cytochrome bc(1) core complex of Rhodobacter sphaeroides contains a fraction of the electron transfer activity of the wild-type enzyme. Addition of subunit IV to the core complex increases electron transfer activity to the same level as that of the wild-type complex. This activity increase may result from subunit IV preventing electron leakage, from the low potential electron transfer chain, and reaction with molecular oxygen, producing superoxide anion. This suggestion is based on the following observations: (1) the extent of cytochrome b reduction in the three-subunit core complex, by ubiquinol, in the presence of antimycin A, never reaches the same level as that in the wild-type complex; (2) the core complex produces 4 times as much superoxide anion as does the wild-type complex; and (3) when the core complex is reconstituted with subunit IVs having varying reconstitutive activities, the activity increase in reconstituted complexes correlates with superoxide production decrease and extent of cytochrome b reduction increase.
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Affiliation(s)
- Ying Yin
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, USA
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22
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Xia D, Esser L, Elberry M, Zhou F, Yu L, Yu CA. The road to the crystal structure of the cytochrome bc1 complex from the anoxigenic, photosynthetic bacterium Rhodobacter sphaeroides. J Bioenerg Biomembr 2008; 40:485-92. [PMID: 18953640 DOI: 10.1007/s10863-008-9180-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2008] [Accepted: 08/01/2008] [Indexed: 10/21/2022]
Abstract
The advantages of using bacterial systems to study the mechanism and function of cytochrome bc (1) complexes do not extend readily to their structural investigations. High quality crystals of bacterial complexes have been difficult to obtain despite the enzymes' smaller sizes and simpler subunit compositions compared to their mitochondrial counterparts. In the course of the structure determination of the bc (1) complex from R. sphaeroides, we observed that the growth of only low quality crystals correlated with low activity and stability of the purified complex, which was mitigated in part by introducing a double mutations to the enzyme. The S287R(cyt b)/V135S(ISP) mutant shows 40% increase in electron transfer activity and displays a 4.3 degrees C increase in thermal stability over wild-type enzyme. The amino acid histidine was found important in maintaining structural integrity of the bacterial complex, while the respiratory inhibitors such as stigmatellin are required for immobilization of the iron-sulfur protein extrinsic domain. Crystal quality of the R. sphaeroides bc (1) complex can be improved further by the presence of strontium ions yielding crystals that diffracted X-rays to better than 2.3 A resolution. The improved crystal quality can be understood in terms of participation of strontium ions in molecular packing arrangement in crystal.
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Affiliation(s)
- Di Xia
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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Yang S, Ma HW, Yu L, Yu CA. On the mechanism of quinol oxidation at the QP site in the cytochrome bc1 complex: studied using mutants lacking cytochrome bL or bH. J Biol Chem 2008; 283:28767-76. [PMID: 18713733 DOI: 10.1074/jbc.m803013200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To elucidate the mechanism of bifurcated oxidation of quinol in the cytochrome bc1 complex, Rhodobacter sphaeroides mutants, H198N and H111N, lacking heme bL and heme bH, respectively, were constructed and characterized. Purified mutant complexes have the same subunit composition as that of the wild-type complex, but have only 9-11% of the electron transfer activity, which is sensitive to stigmatellin or myxothiazol. The Em values for hemes bL and bH in the H111N and H198N complexes are -95 and -35 mV, respectively. The pseudo first-order reduction rate constants for hemes bL and bH in H111N and H198N, by ubiquiniol, are 16.3 and 12.4 s(-1), respectively. These indicate that the Qp site in the H111N mutant complex is similar to that in the wild-type complex. Pre-steady state reduction rates of heme c1 by these two mutant complexes decrease to a similar extent of their activity, suggesting that the decrease in electron transfer activity is due to impairment of movement of the head domain of reduced iron-sulfur protein, caused by disruption of electron transfer from heme bL to heme bH. Both mutant complexes produce as much superoxide as does antimycin A-treated wild-type complex. Ascorbate eliminates all superoxide generating activity in the intact or antimycin inhibited wild-type or mutant complexes.
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Affiliation(s)
- Shaoqing Yang
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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24
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Gurung B, Yu L, Yu CA. Stigmatellin induces reduction of iron-sulfur protein in the oxidized cytochrome bc1 complex. J Biol Chem 2008; 283:28087-94. [PMID: 18701458 DOI: 10.1074/jbc.m804229200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stigmatellin, a Q(P) site inhibitor, inhibits electron transfer from iron-sulfur protein (ISP) to cytochrome c1 in the bc1 complex. Stigmatellin raises the midpoint potential of ISP from 290 mV to 540 mV. The binding of stigmatellin to the fully oxidized complex, oxidized completely by catalytic amounts of cytochrome c oxidase and cytochrome c, results in ISP reduction. The extent of ISP reduction is proportional to the amount of inhibitor used and reaches a maximum when the ratio of inhibitor to enzyme complex reaches unity. A g = 2.005 EPR peak, characteristic of an organic free radical, is also observed when stigmatellin is added to the oxidized complex, and its signal intensity depends on the amount of stigmatellin. Addition of ferricyanide, a strong oxidant, to the oxidized complex also generates a g = 2.005 EPR peak that is oxidant concentration-dependent. Oxygen radicals are generated when stigmatellin is added to the oxidized complex in the absence of the exogenous substrate, ubiquinol. The amount of oxygen radical formed is proportional to the amount of stigmatellin added. Oxygen radicals are not generated when stigmatellin is added to a mutant bc1 complex lacking the Rieske iron-sulfur cluster. Based on these results, it is proposed that ISP becomes a strong oxidant upon stigmatellin binding, extracting electrons from an organic compound, likely an amino acid residue. This results in the reduction of ISP and generation of organic radicals.
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Affiliation(s)
- Buddha Gurung
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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Yu CA, Cen X, Ma HW, Yin Y, Yu L, Esser L, Xia D. Domain conformational switch of the iron-sulfur protein in cytochrome bc1 complex is induced by the electron transfer from cytochrome bL to bH. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:1038-43. [PMID: 18452702 DOI: 10.1016/j.bbabio.2008.03.033] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Revised: 03/06/2008] [Accepted: 03/25/2008] [Indexed: 11/30/2022]
Abstract
Intensive biochemical, biophysical and structural studies of the cytochrome (cyt) bc(1) complex in the past have led to the formulation of the "protonmotive Q-cycle" mechanism for electron and proton transfer in this vitally important complex. The key step of this mechanism is the separation of electrons during the oxidation of a substrate quinol at the Q(P) site with both electrons transferred simultaneously to ISP and cyt b(L) when the extrinsic domain of ISP (ISP-ED) is located at the b-position. Pre-steady state fast kinetic analysis of bc(1) demonstrates that the reduced ISP-ED moves to the c(1)-position to reduce cyt c(1) only after the reduced cyt b(L) is oxidized by cyt b(H). However, the question of how the conformational switch of ISP-ED is initiated remains unanswered. The results obtained from analysis of inhibitory efficacy and binding affinity of two types of Q(P) site inhibitors, Pm and Pf, under various redox states of the bc(1) complex, suggest that the electron transfer from heme b(L) to b(H) is the driving force for the releasing of the reduced ISP-ED from the b-position to c(1)-position to reduce cyt c(1).
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Affiliation(s)
- Chang-An Yu
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, USA.
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26
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Esser L, Elberry M, Zhou F, Yu CA, Yu L, Xia D. Inhibitor-complexed Structures of the Cytochrome bc1 from the Photosynthetic Bacterium Rhodobacter sphaeroides. J Biol Chem 2008; 283:2846-57. [DOI: 10.1074/jbc.m708608200] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Formation of engineered intersubunit disulfide bond in cytochrome bc1 complex disrupts electron transfer activity in the complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:317-26. [PMID: 18258178 DOI: 10.1016/j.bbabio.2008.01.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2007] [Revised: 01/10/2008] [Accepted: 01/11/2008] [Indexed: 11/19/2022]
Abstract
Protein domain movement of the Rieske iron-sulfur protein has been speculated to play an essential role in the bifurcated oxidation of ubiquinol catalyzed by the cytochrome bc1 complex. To better understand the electron transfer mechanism of the bifurcated ubiquinol oxidation at Qp site, we fixed the head domain of ISP at the cyt c1 position by creating an intersubunit disulfide bond between two genetically engineered cysteine residues: one at position 141 of ISP and the other at position 180 of the cyt c1 [S141C(ISP)/G180C(cyt c1)]. The formation of a disulfide bond between ISP and cyt c1 in this mutant complex is confirmed by SDS-PAGE and Western blot. In this mutant complex, the disulfide bond formation is concurrent with the loss of the electron transfer activity of the complex. When the disulfide bond is released by treatment with beta-mercaptoethanol, the activity is restored. These results further support the hypothesis that the mobility of the head domain of ISP is functionally important in the cytochrome bc1 complex. Formation of the disulfide bond between ISP and cyt c1 shortens the distance between the [2Fe-2S] cluster and heme c1, hence the rate of intersubunit electron transfer between these two redox prosthetic groups induced by pH change is increased. The intersubunit disulfide bond formation also decreases the rate of stigmatellin induced reduction of ISP in the fully oxidized complex, suggesting that an endogenous electron donor comes from the vicinity of the b position in the cytochrome b.
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A structural perspective on mechanism and function of the cytochrome bc (1) complex. Results Probl Cell Differ 2007; 45:253-78. [PMID: 18038116 DOI: 10.1007/400_2007_042] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The cytochrome bc (1) complex is a fundamental component of the energy conversion machinery of respiratory and photosynthetic electron transfer chains. The multi-subunit membrane protein complex couples electron transfer from hydroquinone to cytochrome c to the translocation of protons across the membrane, thereby substantially contributing to the proton motive force that is used for ATP synthesis. Considerable progress has been made with structural and functional studies towards complete elucidation of the Q cycle mechanism, which was originally proposed by Mitchell 30 years ago. Yet, open questions regarding key steps of the mechanism still remain. The role of the complex as a major source of reactive oxygen species and its implication in pathophysiological conditions has recently gained interest.
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Xia D, Esser L, Yu L, Yu CA. Structural basis for the mechanism of electron bifurcation at the quinol oxidation site of the cytochrome bc1 complex. PHOTOSYNTHESIS RESEARCH 2007; 92:17-34. [PMID: 17457691 DOI: 10.1007/s11120-007-9155-3] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Accepted: 03/01/2007] [Indexed: 05/15/2023]
Abstract
At the heart of the Q cycle hypothesis, the cytochrome bc1 complex (bc1) is required to separate the two electrons from a quinol molecule at the quinol oxidation site. Recent studies have brought to light an intricate mechanism for this bifurcated electron transfer. A survey of the protein data bank shows 30 entries for the structures of bc1 and the homologous b6 f complex. These structures provide considerable insights into the structural organization of mitochondrial, bacterial, and plant enzymes. Crystallographic binding studies of bc1 with either quinone reduction (QN) and/or quinol oxidation (QP) site inhibitors offer atomic details on how these compounds interact with residues at their respective sites. Most importantly, the different locations and apparent flexibility observed in crystals for the extrinsic domain of the iron-sulfur protein (ISP) subunit suggest a mechanism for electron bifurcation at the QP site. Analyses of various inhibitor-bound structures revealed two classes of QP site inhibitors: Pm inhibitors that promote ISP mobility and Pf inhibitors that favor the fixation of the ISP conformation. Those analyses also shed light on a possible process by which the ISP motion switch is controlled. The first phase reduction of ISP is shown to be comparable to the reduction of the bL heme by pre-steady state kinetic analysis, whereas the second phase reduction of ISP share similar kinetics with the reduction of the bH heme. The reduction of cyt c1 is measured much slower, indicating that the reduced ISP remains bound at the QP site until the reduced heme bL is oxidized by the heme bH and supporting the existence of a control mechanism for the ISP motion switch.
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Affiliation(s)
- Di Xia
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, NIH, 37 Convent Dr., Building 37, Room 2122C, Bethesda, MD 20892, USA.
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Rajagukguk S, Yang S, Yu CA, Yu L, Durham B, Millett F. Effect of mutations in the cytochrome b ef loop on the electron-transfer reactions of the Rieske iron-sulfur protein in the cytochrome bc1 complex. Biochemistry 2007; 46:1791-8. [PMID: 17253777 PMCID: PMC2527182 DOI: 10.1021/bi062094g] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Long-range movement of the Rieske iron-sulfur protein (ISP) between the cytochrome (cyt) b and cyt c1 redox centers plays a key role in electron transfer within the cyt bc1 complex. A series of 21 mutants in the cyt b ef loop of Rhodobacter sphaeroides cyt bc1 were prepared to examine the role of this loop in controlling the capture and release of the ISP from cyt b. Electron transfer in the cyt bc1 complex was studied using a ruthenium dimer to rapidly photo-oxidize cyt c1 within 1 mus and initiate the reaction. The rate constant for electron transfer from the Rieske iron-sulfur center [2Fe2S] to cyt c1 was k1 = 60 000 s-1. Famoxadone binding to the Qo site decreases k1 to 5400 s-1, indicating that a conformational change on the surface of cyt b decreases the rate of release of the ISP from cyt b. The mutation I292A on the surface of the ISP-binding crater decreased k1 to 4400 s-1, while the addition of famoxadone further decreased it to 3000 s-1. The mutation L286A at the tip of the ef loop decreased k1 to 33 000 s-1, but famoxadone binding caused no further decrease, suggesting that this mutation blocked the conformational change induced by famoxadone. Studies of all of the mutants provide further evidence that the ef loop plays an important role in regulating the domain movement of the ISP to facilitate productive electron transfer and prevent short-circuit reactions.
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Affiliation(s)
- Sany Rajagukguk
- Department of Chemistry and Biochemistry University of Arkansas Fayetteville, Arkansas 72701
| | - Shaoqing Yang
- Department of Biochemistry and Molecular Biology Oklahoma State University Stillwater, Oklahoma 74078
| | - Chang-An Yu
- Department of Biochemistry and Molecular Biology Oklahoma State University Stillwater, Oklahoma 74078
| | - Linda Yu
- Department of Biochemistry and Molecular Biology Oklahoma State University Stillwater, Oklahoma 74078
| | - Bill Durham
- Department of Chemistry and Biochemistry University of Arkansas Fayetteville, Arkansas 72701
| | - Francis Millett
- Department of Chemistry and Biochemistry University of Arkansas Fayetteville, Arkansas 72701
- To whom correspondence should be addressed FAX: 479−575−4049, Phone: 479−575−4999, E-mail:
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Esser L, Gong X, Yang S, Yu L, Yu CA, Xia D. Surface-modulated motion switch: capture and release of iron-sulfur protein in the cytochrome bc1 complex. Proc Natl Acad Sci U S A 2006; 103:13045-50. [PMID: 16924113 PMCID: PMC1551902 DOI: 10.1073/pnas.0601149103] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the cytochrome bc(1) complex, the swivel motion of the iron-sulfur protein (ISP) between two redox sites constitutes a key component of the mechanism that achieves the separation of the two electrons in a substrate molecule at the quinol oxidation (Q(o)) site. The question remaining is how the motion of ISP is controlled so that only one electron enters the thermodynamically favorable chain via ISP. An analysis of eight structures of mitochondrial bc(1) with bound Q(o) site inhibitors revealed that the presence of inhibitors causes a bidirectional repositioning of the cd1 helix in the cytochrome b subunit. As the cd1 helix forms a major part of the ISP binding crater, any positional shift of this helix modulates the ability of cytochrome b to bind ISP. The analysis also suggests a mechanism for reversal of the ISP fixation when the shape complementarity is significantly reduced after a positional reorientation of the reaction product quinone. The importance of shape complementarity in this mechanism was confirmed by functional studies of bc(1) mutants and by a structure determination of the bacterial form of bc(1). A mechanism for the high fidelity of the bifurcated electron transfer is proposed.
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Affiliation(s)
- Lothar Esser
- *Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892; and
| | - Xing Gong
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078
| | - Shaoqing Yang
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078
| | - Linda Yu
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078
| | - Chang-An Yu
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078
- To whom correspondence may be addressed. E-mail:
| | - Di Xia
- *Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892; and
- To whom correspondence may be addressed at:
Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Building 37, Room 2122C, Bethesda, MD 20892. E-mail:
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Crofts AR, Lhee S, Crofts SB, Cheng J, Rose S. Proton pumping in the bc1 complex: A new gating mechanism that prevents short circuits. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:1019-34. [PMID: 16600173 DOI: 10.1016/j.bbabio.2006.02.009] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Revised: 02/03/2006] [Accepted: 02/16/2006] [Indexed: 11/25/2022]
Abstract
The Q-cycle mechanism of the bc1 complex explains how the electron transfer from ubihydroquinone (quinol, QH2) to cytochrome (cyt) c (or c2 in bacteria) is coupled to the pumping of protons across the membrane. The efficiency of proton pumping depends on the effectiveness of the bifurcated reaction at the Q(o)-site of the complex. This directs the two electrons from QH2 down two different pathways, one to the high potential chain for delivery to an electron acceptor, and the other across the membrane through a chain containing heme bL and bH to the Qi-site, to provide the vectorial charge transfer contributing to the proton gradient. In this review, we discuss problems associated with the turnover of the bc1 complex that center around rates calculated for the normal forward and reverse reactions, and for bypass (or short-circuit) reactions. Based on rate constants given by distances between redox centers in known structures, these appeared to preclude conventional electron transfer mechanisms involving an intermediate semiquinone (SQ) in the Q(o)-site reaction. However, previous research has strongly suggested that SQ is the reductant for O2 in generation of superoxide at the Q(o)-site, introducing an apparent paradox. A simple gating mechanism, in which an intermediate SQ mobile in the volume of the Q(o)-site is a necessary component, can readily account for the observed data through a coulombic interaction that prevents SQ anion from close approach to heme bL when the latter is reduced. This allows rapid and reversible QH2 oxidation, but prevents rapid bypass reactions. The mechanism is quite natural, and is well supported by experiments in which the role of a key residue, Glu-295, which facilitates proton transfer from the site through a rotational displacement, has been tested by mutation.
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Affiliation(s)
- Antony R Crofts
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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Elberry M, Xiao K, Esser L, Xia D, Yu L, Yu CA. Generation, characterization and crystallization of a highly active and stable cytochrome bc1 complex mutant from Rhodobacter sphaeroides. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:835-40. [PMID: 16828701 DOI: 10.1016/j.bbabio.2006.05.031] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2006] [Revised: 05/11/2006] [Accepted: 05/12/2006] [Indexed: 11/21/2022]
Abstract
The availability of the three dimensional structure of mitochondrial enzyme, obtained by X-ray crystallography, allowed a significant progress in the understanding of the structure-function relation of the cytochrome bc(1) complex. Most of the structural information obtained has been confirmed by molecular genetic studies of the bacterial complex. Despite its small size and simple subunit composition, high quality crystals of the bacterial complex have been difficult to obtain and so far, only low resolution structural data has been reported. The low quality crystal observed is likely associated in part with the low activity and stability of the purified complex. To mitigate this problem, we recently engineered a mutant [S287R(cytb)/V135S(ISP)] from Rhodobacter sphaeroides to produce a highly active and more stable cytochrome bc(1) complex. The purified mutant complex shows a 40% increase in electron transfer activity as compared to that of the wild type enzyme. Differential scanning calorimetric study shows that the mutant is more stable than the wild type complex as indicated by a 4.3 degrees C increase in the thermo-denaturation temperature. Crystals formed from this mutant complex, in the presence of stigmatellin, diffract X-rays up to 2.9 Angstroms resolution.
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Affiliation(s)
- Maria Elberry
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, 74078, USA
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Tso SC, Yin Y, Yu CA, Yu L. Identification of amino acid residues essential for reconstitutive activity of subunit IV of the cytochrome bc1 complex from Rhodobacter sphaeroides. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:1561-7. [PMID: 16890186 DOI: 10.1016/j.bbabio.2006.06.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2006] [Revised: 05/30/2006] [Accepted: 06/01/2006] [Indexed: 11/28/2022]
Abstract
A region of subunit IV comprising residues 77-85 is identified as essential for interaction with the core complex to restore the bc(1) activity (reconstitutive activity). Recombinant subunit IV mutants with single or multiple alanine substitution at this region were generated and characterized to identify the essential amino acid residues. Residues 81-84, with sequence of YRYR, are required for reconstitutive activity of subunit IV, because a mutant with these four residues substituted with alanine has little activity, while a mutant with alanine substitution at residues 77-80 and 85 have the same reconstitutive activity as that of the wild-type IV. The positively charged group at R-82 and R-84 and both the hydroxyl group and aromatic group at Y-81 and Y-83 are essential. The interactions between these four residues of subunit IV and residues of core subunits are also responsible for the stability of the complex. However, these interactions are not essential for the incorporation of subunit IV into the bc(1) complex.
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Affiliation(s)
- Shih-Chia Tso
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, USA
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35
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Mulkidjanian AY. Ubiquinol oxidation in the cytochrome bc1 complex: Reaction mechanism and prevention of short-circuiting. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1709:5-34. [PMID: 16005845 DOI: 10.1016/j.bbabio.2005.03.009] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2004] [Revised: 12/01/2004] [Accepted: 03/22/2005] [Indexed: 11/26/2022]
Abstract
This review is focused on the mechanism of ubiquinol oxidation by the cytochrome bc1 complex (bc1). This integral membrane complex serves as a "hub" in the vast majority of electron transfer chains. The bc1 oxidizes a ubiquinol molecule to ubiquinone by a unique "bifurcated" reaction where the two released electrons go to different acceptors: one is accepted by the mobile redox active domain of the [2Fe-2S] iron-sulfur Rieske protein (FeS protein) and the other goes to cytochrome b. The nature of intermediates in this reaction remains unclear. It is also debatable how the enzyme prevents short-circuiting that could happen if both electrons escape to the FeS protein. Here, I consider a reaction mechanism that (i) agrees with the available experimental data, (ii) entails three traits preventing the short-circuiting in bc1, and (iii) exploits the evident structural similarity of the ubiquinone binding sites in the bc1 and the bacterial photosynthetic reaction center (RC). Based on the latter congruence, it is suggested that the reaction route of ubiquinol oxidation by bc1 is a reversal of that leading to the ubiquinol formation in the RC. The rate-limiting step of ubiquinol oxidation is then the re-location of a ubiquinol molecule from its stand-by site within cytochrome b into a catalytic site, which is formed only transiently, after docking of the mobile redox domain of the FeS protein to cytochrome b. In the catalytic site, the quinone ring is stabilized by Glu-272 of cytochrome b and His-161 of the FeS protein. The short circuiting is prevented as long as: (i) the formed semiquinone anion remains bound to the reduced FeS domain and impedes its undocking, so that the second electron is forced to go to cytochrome b; (ii) even after ubiquinol is fully oxidized, the reduced FeS domain remains docked to cytochrome b until electron(s) pass through cytochrome b; (iii) if cytochrome b becomes (over)reduced, the binding and oxidation of further ubiquinol molecules is hampered; the reason is that the Glu-272 residue is turned towards the reduced hemes of cytochrome b and is protonated to stabilize the surplus negative charge; in this state, this residue cannot participate in the binding/stabilization of a ubiquinol molecule.
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Affiliation(s)
- Armen Y Mulkidjanian
- Max Planck Institute of Biophysics, Department of Biophysical Chemistry, Max-von-Laue-Str. 3, D-60438 Frankfurt-am-Main, Germany.
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Gurung B, Yu L, Xia D, Yu CA. The iron-sulfur cluster of the Rieske iron-sulfur protein functions as a proton-exiting gate in the cytochrome bc(1) complex. J Biol Chem 2005; 280:24895-902. [PMID: 15878858 DOI: 10.1074/jbc.m503319200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The destruction of the Rieske iron-sulfur cluster ([2Fe-2S]) in the bc(1) complex by hematoporphyrin-promoted photoinactivation resulted in the complex becoming proton-permeable. To study further the role of this [2Fe-2S] cluster in proton translocation of the bc(1) complex, Rhodobacter sphaeroides mutants expressing His-tagged cytochrome bc(1) complexes with mutations at the histidine ligands of the [2Fe-2S] cluster were generated and characterized. These mutants lacked the [2Fe-2S] cluster and possessed no bc(1) activity. When the mutant complex was co-inlaid in phospholipid vesicles with intact bovine mitochondrial bc(1) complex or cytochrome c oxidase, the proton ejection, normally observed in intact reductase or oxidase vesicles during the oxidation of their corresponding substrates, disappeared. This indicated the creation of a proton-leaking channel in the mutant complex, whose [2Fe-2S] cluster was lacking. Insertion of the bc(1) complex lacking the head domain of the Rieske iron-sulfur protein, removed by thermolysin digestion, into PL vesicles together with mitochondrial bc(1) complex also rendered the vesicles proton-permeable. Addition of the excess purified head domain of the Rieske iron-sulfur protein partially restored the proton-pumping activity. These results indicated that elimination of the [2Fe-2S] cluster in mutant bc(1) complexes opened up an otherwise closed proton channel within the bc(1) complex. It was speculated that in the normal catalytic cycle of the bc(1) complex, the [2Fe-2S] cluster may function as a proton-exiting gate.
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Affiliation(s)
- Buddha Gurung
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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37
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Gong X, Yu L, Xia D, Yu CA. Evidence for electron equilibrium between the two hemes bL in the dimeric cytochrome bc1 complex. J Biol Chem 2004; 280:9251-7. [PMID: 15615714 DOI: 10.1074/jbc.m409994200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Structural analysis of the dimeric mitochondrial cytochrome bc1 complex suggests that electron transfer between inter-monomer hemes bL-bL may occur during bc1 catalysis. Such electron transfer may be facilitated by the aromatic pairs present between the two bL hemes in the two symmetry-related monomers. To test this hypothesis, R. sphaeroides mutants expressing His6-tagged bc1 complexes with mutations at three aromatic residues (Phe-195, Tyr-199, and Phe-203), located between two bL hemes, were generated and characterized. All three mutants grew photosynthetically at a rate comparable to that of wild-type cells. The bc1 complexes prepared from mutants F195A, Y199A, and F203A have, respectively, 78%, 100%, and 100% of ubiquinol-cytochrome c reductase activity found in the wild-type complex. Replacing the Phe-195 of cytochrome b with Tyr, His, or Trp results in mutant complexes (F195Y, F195H, or F195W) having the same ubiquinol-cytochrome c reductase activity as the wild-type. These results indicate that the aromatic group at position195 of cytochrome b is involved in electron transfer reactions of the bc1 complex. The rate of superoxide anion (O2*) generation, measured by the chemiluminescence of 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-alpha]pyrazin-3-one hydrochloride-O2* adduct during oxidation of ubiquinol, is 3 times higher in the F195A complex than in the wild-type or mutant complexes Y199A or F203A. This supports the idea that the interruption of electron transfer between the two bL hemes enhances electron leakage to oxygen and thus decreases the ubiquinol-cytochrome c reductase activity.
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Affiliation(s)
- Xing Gong
- Department of Biochemistry & Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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38
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Liu X, Yu CA, Yu L. The Role of Extra Fragment at the C-terminal of Cytochrome b (Residues 421–445) in the Cytochrome bc1 Complex from Rhodobacter sphaeroides. J Biol Chem 2004; 279:47363-71. [PMID: 15339929 DOI: 10.1074/jbc.m406497200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sequence alignment of cytochrome b of the cytochrome bc1 complex from various sources reveals that bacterial cytochrome b contain an extra fragment at the C terminus. To study the role of this fragment in bacterial cytochrome bc1 complex, Rhodobacter sphaeroides mutants expressing His-tagged cytochrome bc1 complexes with progressive deletion from this fragment (residues 421-445) were generated and characterized. The cytbDelta-(433-445) bc1 complex, in which 13 residues from the C-terminal end of this fragment are deleted, has electron transfer activity, subunit composition, and physical properties similar to those of the complement complex, indicating that this region of the extra fragment is not essential. In contrast, the electron transfer activity, binding of cytochrome b, ISP, and subunit IV to cytochrome c1, redox potentials of cytochromes b and c1 in the cytbDelta-(427-445), cytbDelta-(425-445), and cytbDelta-(421-445) mutant complexes, in which 19, 21, or all residues of this fragment are deleted, decrease progressively. EPR spectra of the [2Fe-2S] cluster and the cytochromes b in these three deletion mutant bc1 complexes are also altered; the extent of spectral alteration increases as this extra fragment is shortened. These results indicate that the first 12 residues (residues 421-432) from the N-terminal end of the C-terminal extra fragment of cytochrome b are essential for maintaining structural integrity of the bc1 complex.
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Affiliation(s)
- Xiaoying Liu
- Department of Biochemistry & Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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39
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Esser L, Quinn B, Li YF, Zhang M, Elberry M, Yu L, Yu CA, Xia D. Crystallographic studies of quinol oxidation site inhibitors: a modified classification of inhibitors for the cytochrome bc(1) complex. J Mol Biol 2004; 341:281-302. [PMID: 15312779 DOI: 10.1016/j.jmb.2004.05.065] [Citation(s) in RCA: 191] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2004] [Revised: 05/24/2004] [Accepted: 05/26/2004] [Indexed: 10/26/2022]
Abstract
Cytochrome bc(1) is an integral membrane protein complex essential for cellular respiration and photosynthesis; it couples electron transfer from quinol to cytochrome c to proton translocation across the membrane. Specific bc(1) inhibitors have not only played crucial roles in elucidating the mechanism of bc(1) function but have also provided leads for the development of novel antibiotics. Crystal structures of bovine bc(1) in complex with the specific Q(o) site inhibitors azoxystrobin, MOAS, myxothiazol, stigmatellin and 5-undecyl-6-hydroxy-4,7-dioxobenzothiazole were determined. Interactions, conformational changes and possible mechanisms of resistance, specific to each inhibitor, were defined. Residues and secondary structure elements that are capable of discriminating different classes of Q(o) site inhibitors were identified for the cytochrome b subunit. Directions in the displacement of the cd1 helix of cytochrome b subunit in response to various Q(o) site inhibitors were correlated to the binary conformational switch of the extrinsic domain of the iron-sulfur protein subunit. The new structural information, together with structures previously determined, provide a basis that, combined with biophysical and mutational data, suggest a modification to the existing classification of bc(1) inhibitors. bc(1) inhibitors are grouped into three classes: class P inhibitors bind to the Q(o) site, class N inhibitors bind to the Q(i) site and the class PN inhibitors target both sites. Class P contains two subgroups, Pm and Pf, that are distinct by their ability to induce mobile or fixed conformation of iron-sulfur protein.
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Affiliation(s)
- Lothar Esser
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA
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40
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Ebert CE, Beattie DS. A compensatory double mutation of the alanine-86 to leucine mutant located in the hinge region of the iron-sulfur protein of the yeast cytochrome bc1 complex. Arch Biochem Biophys 2004; 429:16-22. [PMID: 15288805 DOI: 10.1016/j.abb.2004.04.031] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2004] [Revised: 04/16/2004] [Indexed: 10/26/2022]
Abstract
Mutations in the hinge region connecting the membrane anchor to the extra-membranous head-group of the iron-sulfur protein can impede proper assembly and function of the cytochrome bc(1) complex. Mutating the conserved alanines, residues 86, 90, and 92, located in the hinge region resulted in a 30-50% decrease in enzymatic activity without loss of the iron-sulfur protein [J. Bioenerg. Biomembr. 31 (1999) 215]. The lowered enzymatic activity in the A86L mutant was shown to result from steric interference between the side chains of Leu-86 and Leu-89 [Biochemistry 40 (2001) 327]. The compensatory double mutant A86L/L89A restored activity to wild type levels and relieved the steric hindrance; however, the L89A mutant did not assemble properly into the bc(1) complex. Molecular modeling studies of these mutants compared to the wild type have suggested that the hydrophobic residues located in the hinge region are critical to the motion of the head group of the iron-sulfur protein during catalysis.
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Affiliation(s)
- C Edward Ebert
- Department of Biochemistry and Molecular Pharmacology, West Virginia University School of Medicine, Morgantown, WV 26506-9142, USA
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Schneider D, Berry S, Volkmer T, Seidler A, Rögner M. PetC1 is the major Rieske iron-sulfur protein in the cytochrome b6f complex of Synechocystis sp. PCC 6803. J Biol Chem 2004; 279:39383-8. [PMID: 15262969 DOI: 10.1074/jbc.m406288200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many of the completely sequenced cyanobacterial genomes contain a gene family that encodes for putative Rieske iron-sulfur proteins. The Rieske protein is one of the large subunits of the cytochrome bc-type complexes involved in respiratory and photosynthetic electron transfer. In contrast to all other subunits of this complex that are encoded by single genes, the genome of the cyanobacterium Synechocystis PCC 6803 contains three petC genes, all encoding potential Rieske subunits. Most interestingly, any of the petC genes can be deleted individually without altering the Synechocystis phenotype dramatically. In contrast, double deletion experiments revealed that petC1 and petC2 cannot be deleted in combination, whereas petC3 can be deleted together with any of the other two petC genes. Further results suggest a different physiological function for each of the Rieske proteins. Whereas PetC2 can partly replace the dominating Rieske isoform PetC1, PetC3 is unable to functionally replace either PetC1 or PetC2 and may have a special function involving a special donor with a lower redox potential than plastoquinone. A predominant role of PetC1, which is (partly) different from PetC2, is suggested by the mutational analysis and a detailed characterization of the electron transfer reactions in the mutant strains.
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Affiliation(s)
- Dirk Schneider
- Lehrstuhl für Biochemie der Pflanzen, Ruhr-Universität Bochum, Germany.
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Brasseur G, Lemesle-Meunier D, Reinaud F, Meunier B. QO Site Deficiency Can Be Compensated by Extragenic Mutations in the Hinge Region of the Iron-Sulfur Protein in the bc1 Complex of Saccharomyces cerevisiae. J Biol Chem 2004; 279:24203-11. [PMID: 15039445 DOI: 10.1074/jbc.m311576200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial bc(1) complex catalyzes the oxidation of ubiquinol and the reduction of cytochrome (cyt) c. The cyt b mutation A144F has been introduced in yeast by the biolistic method. This residue is located in the cyt b cd(1) amphipathic helix in the quinol-oxidizing (Q(O)) site. The resulting mutant was respiration-deficient and was affected in the quinol binding and electron transfer rates at the Q(O) site. An intragenic suppressor mutation was selected (A144F+F179L) that partially alleviated the defect of quinol oxidation of the original mutant A144F. The suppressor mutation F179L, located at less than 4 A from A144F, is likely to compensate directly the steric hindrance caused by phenylalanine at position 144. A second set of suppressor mutations was obtained, which also partially restored the quinol oxidation activity of the bc(1) complex. They were located about 20 A from A144F in the hinge region of the iron-sulfur protein (ISP) between residues 85 and 92. This flexible region is crucial for the movement of the ISP between cyt b and cyt c(1) during enzyme turnover. Our results suggested that the compensatory effect of the mutations in ISP was due to the repositioning of this subunit on cyt b during quinol oxidation. This genetic and biochemical study thus revealed the close interaction between the cyt b cd(1) helix in the quinol-oxidizing Q(O) site and the ISP via the flexible hinge region and that fine-tuning of the Q(O) site catalysis can be achieved by subtle changes in the linker domain of the ISP.
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Affiliation(s)
- Gaël Brasseur
- Laboratoire de Bioénergétique et Ingénierie des Protéines, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
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Crofts AR. Proton-coupled electron transfer at the Qo-site of the bc1 complex controls the rate of ubihydroquinone oxidation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2004; 1655:77-92. [PMID: 15100020 DOI: 10.1016/j.bbabio.2003.10.012] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2003] [Revised: 09/29/2003] [Accepted: 10/27/2003] [Indexed: 10/26/2022]
Abstract
The rate-limiting reaction of the bc(1) complex from Rhodobacter sphaeroides is transfer of the first electron from ubihydroquinone (quinol, QH(2)) to the [2Fe-2S] cluster of the Rieske iron-sulfur protein (ISP) at the Q(o)-site. Formation of the ES-complex requires participation of two substrates (S), QH(2) and ISP(ox). From the variation of rate with [S], the binding constants for both substrates involved in formation of the complex can be estimated. The configuration of the ES-complex likely involves the dissociated form of the oxidized ISP (ISP(ox)) docked at the b-interface on cyt b, in a complex in which N(epsilon) of His-161 (bovine sequence) forms a H-bond with the quinol -OH. A coupled proton and electron transfer occurs along this H-bond. This brief review discusses the information available on the nature of this reaction from kinetic, structural and mutagenesis studies. The rate is much slower than expected from the distance involved, likely because it is controlled by the low probability of finding the proton in the configuration required for electron transfer. A simplified treatment of the activation barrier is developed in terms of a probability function determined by the Brønsted relationship, and a Marcus treatment of the electron transfer step. Incorporation of this relationship into a computer model allows exploration of the energy landscape. A set of parameters including reasonable values for activation energy, reorganization energy, distances between reactants, and driving forces, all consistent with experimental data, explains why the rate is slow, and accounts for the altered kinetics in mutant strains in which the driving force and energy profile are modified by changes in E(m) and/or pK of ISP or heme b(L).
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Affiliation(s)
- Antony R Crofts
- Department of Biochemistry and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, 419 Roger Adams Lab, 600 S. Mathews Avenue, Urbana, IL 61801, USA.
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Fisher N, Bourges I, Hill P, Brasseur G, Meunier B. Disruption of the interaction between the Rieske iron-sulfur protein and cytochrome b in the yeast bc1 complex owing to a human disease-associated mutation within cytochrome b. ACTA ACUST UNITED AC 2004; 271:1292-8. [PMID: 15030479 DOI: 10.1111/j.1432-1033.2004.04036.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The mitochondrial cytochrome b missense mutation, G167E, has been reported in a patient with cardiomyopathy. The residue G167 is located in an extramembranous helix close to the hinge region of the iron-sulfur protein. In order to characterize the effects of the mutation on the structure and function of the bc(1) complex, we introduced G167E into the highly similar yeast cytochrome b. The mutation had a severe effect on the respiratory function, with the activity of the bc(1) complex decreased to a few per cent of the wild type. Analysis of the enzyme activity indicated that the mutation affected its stability, which could be the result of an altered binding of the iron-sulfur protein on the complex. G167E had no major effect on the interaction between the iron-sulfur protein headgroup and the quinol oxidation site, as judged by the electron paramagnetic resonance signal, and only a minor effect on the rate of cytochrome b reduction, but it severely reduced the rate of cytochrome c(1) reduction. This suggested that the mutation G167E could hinder the movement of the iron-sulfur protein, probably by distorting the structure of the hinge region. The function of bc(1) was partially restored by mutations (W164L and W166L) located close to the primary change, which reduced the steric hindrance caused by G167E. Taken together, these observations suggest that the protein-protein interaction between the n-sulfur protein hinge region and the cytochrome b extramembranous cd2 helix is important for maintaining the structure of the hinge region and, by consequence, the movement of the headgroup and the integrity of the enzyme.
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Affiliation(s)
- Nicholas Fisher
- Wolfson Institute for Biomedical Research, University College London, UK
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Abstract
The bc1 complexes are intrinsic membrane proteins that catalyze the oxidation of ubihydroquinone and the reduction of cytochrome c in mitochondrial respiratory chains and bacterial photosynthetic and respiratory chains. The bc1 complex operates through a Q-cycle mechanism that couples electron transfer to generation of the proton gradient that drives ATP synthesis. Genetic defects leading to mutations in proteins of the respiratory chain, including the subunits of the bc1 complex, result in mitochondrial myopathies, many of which are a direct result of dysfunction at catalytic sites. Some myopathies, especially those in the cytochrome b subunit, exacerbate free-radical damage by enhancing superoxide production at the ubihydroquinone oxidation site. This bypass reaction appears to be an unavoidable feature of the reaction mechanism. Cellular aging is largely attributable to damage to DNA and proteins from the reactive oxygen species arising from superoxide and is a major contributing factor in many diseases of old age. An understanding of the mechanism of the bc1 complex is therefore central to our understanding of the aging process. In addition, a wide range of inhibitors that mimic the quinone substrates are finding important applications in clinical therapy and agronomy. Recent structural studies have shown how many of these inhibitors bind, and have provided important clues to the mechanism of action and the basis of resistance through mutation. This paper reviews recent advances in our understanding of the mechanism of the bc1 complex and their relation to these physiologically important issues in the context of the structural information available.
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Affiliation(s)
- Antony R Crofts
- Department of Biochemistry, and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
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Crofts AR, Shinkarev VP, Kolling DRJ, Hong S. The modified Q-cycle explains the apparent mismatch between the kinetics of reduction of cytochromes c1 and bH in the bc1 complex. J Biol Chem 2003; 278:36191-201. [PMID: 12829696 DOI: 10.1074/jbc.m305461200] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Crystallographic structures of the bc1 complex from different sources have provided evidence that a movement of the Rieske iron-sulfur protein (ISP) extrinsic domain is essential for catalysis. This dynamic feature has opened up the question of what limits electron transfer, and several authors have suggested that movement of the ISP head, or gating of such movement, is rate-limiting. Measurements of the kinetics of cytochromes and of the electrochromic shift of carotenoids, following flash activation through the reaction center in chromatophore membranes from Rhodobacter sphaeroides, have allowed us to demonstrate that: (i) ubiquinol oxidation at the Qo-site of the bc1 complex has the same rate in the absence or presence of antimycin bound at the Qi-site, and is the reaction limiting turnover. (ii) Activation energies for transient processes to which movement of the ISP must contribute are much lower than that of the rate-limiting step. (iii) Comparison of experimental data with a simple mathematical model demonstrates that the kinetics of reduction of cytochromes c1 and bH are fully explained by the modified Q-cycle. (iv) All rates for processes associated with movement of the ISP are more rapid by at least an order of magnitude than the rate of ubiquinol oxidation. (v) Movement of the ISP head does not introduce a significant delay in reduction of the high potential chain by quinol, and it is not necessary to invoke such a delay to explain the kinetic disparity between the kinetics of reduction of cytochromes c1 and bH.
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Affiliation(s)
- Antony R Crofts
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
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Maneli MH, Corrigall AV, Klump HH, Davids LM, Kirsch RE, Meissner PN. Kinetic and physical characterisation of recombinant wild-type and mutant human protoporphyrinogen oxidases. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1650:10-21. [PMID: 12922165 DOI: 10.1016/s1570-9639(03)00186-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The effects of various protoporphyrinogen oxidase (PPOX) mutations responsible for variegate porphyria (VP), the roles of the arginine-59 residue and the glycines in the conserved flavin binding site, in catalysis and/or cofactor binding, were examined. Wild-type recombinant human PPOX and a selection of mutants were generated, expressed, purified and partially characterised. All mutants had reduced PPOX activity to varying degrees. However, the activity data did not correlate with the ability/inability to bind flavin. The positive charge at arginine-59 appears to be directly involved in catalysis and not in flavin-cofactor binding alone. The K(m)s for the arginine-59 mutants suggested a substrate-binding problem. T(1/2) indicated that arginine-59 is required for the integrity of the active site. The dominant alpha-helical content was decreased in the mutants. The degree of alpha-helix did not correlate linearly with T(1/2) nor T(m) values, supporting the suggestion that arginine-59 is important for catalysis at the active site. Examination of the conserved dinucleotide-binding sequence showed that substitution of glycine in codon 14 was less disruptive than substitutions in codons 9 and 11. Ultraviolet melting curves generally showed a two-state transition suggesting formation of a multi-domain structure. All mutants studied were more resistant to thermal denaturation compared to wild type, except for R168C.
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Affiliation(s)
- Mbulelo H Maneli
- Lennox Eales Porphyria Laboratories, MRC/UCT Liver Research Centre, Department of Medicine, University of Cape Town Medical School, K-floor, Old GSH Main Building, Observatory 7925, South Africa
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Yan J, Cramer WA. Functional insensitivity of the cytochrome b6f complex to structure changes in the hinge region of the Rieske iron-sulfur protein. J Biol Chem 2003; 278:20925-33. [PMID: 12672829 DOI: 10.1074/jbc.m212616200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Structure analysis of the cytochrome bc1 complex in the presence and absence of Qp quinol analog inhibitors implied that a large amplitude motion of the Rieske iron-sulfur protein (ISP) is required to mediate electron transfer from ubiquinol to cytochrome c1. Studies of the functional consequences of mutagenesis of an 8-residue ISP "hinge" region in the bc1 complex showed it to be sensitive to structure perturbation, implying that optimum flexibility and length are required for the large amplitude motion. Mutagenesis-function analysis carried out on the ISP hinge region of the cytochrome b6 f complex using the cyanobacterium Synechococcus sp. PCC 7002 showed the following. (i) Of three petC genes, only that in the petCA operon codes for functional ISP. (ii) The function of the complex was insensitive to changes in the hinge region that increased flexibility, decreased flexibility by substitutions of 4-6 Pro residues, shortened the hinge by a 1-residue deletion, or elongated it by insertion of 4 residues. The latter change increased sensitivity to Qp inhibitors, whereas deletion of 2 residues resulted in a loss of inhibitor sensitivity and a decrease in activity, indicating a minimum hinge length of 7 residues required for optimum binding of ISP at the Qp site. Thus, in contrast to the bc1 complex, the function of the b6 f complex was insensitive to sequence changes in the ISP hinge that altered its length or flexibility. This implies that either the barriers to motion or the amplitude of ISP motion required for function is smaller than in the bc1 complex.
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Affiliation(s)
- Jiusheng Yan
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-2054,USA
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Xiao K, Engstrom G, Rajagukguk S, Yu CA, Yu L, Durham B, Millett F. Effect of famoxadone on photoinduced electron transfer between the iron-sulfur center and cytochrome c1 in the cytochrome bc1 complex. J Biol Chem 2003; 278:11419-26. [PMID: 12525495 DOI: 10.1074/jbc.m211620200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Famoxadone is a new cytochrome bc(1) Q(o) site inhibitor that immobilizes the iron-sulfur protein (ISP) in the b conformation. The effects of famoxadone on electron transfer between the iron-sulfur center (2Fe-2S) and cyt c(1) were studied using a ruthenium dimer to photoinitiate the reaction. The rate constant for electron transfer in the forward direction from 2Fe-2S to cyt c(1) was found to be 16,000 s(-1) in bovine cyt bc(1). Binding famoxadone decreased this rate constant to 1,480 s(-1), consistent with a decrease in mobility of the ISP. Reverse electron transfer from cyt c(1) to 2Fe-2S was found to be biphasic in bovine cyt bc(1) with rate constants of 90,000 and 7,300 s(-1). In the presence of famoxadone, reverse electron transfer was monophasic with a rate constant of 1,420 s(-1). It appears that the rate constants for the release of the oxidized and reduced ISP from the b conformation are the same in the presence of famoxadone. The effects of famoxadone binding on electron transfer were also studied in a series of Rhodobacter sphaeroides cyt bc(1) mutants involving residues at the interface between the Rieske protein and cyt c(1) and/or cyt b.
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Affiliation(s)
- Kunhong Xiao
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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Soriano GM, Guo LW, De Vitry C, Kallas T, Cramer WA. Electron transfer from the Rieske iron-sulfur protein (ISP) to cytochrome f in vitro. Is a guided trajectory of the ISP necessary for competent docking? J Biol Chem 2002; 277:41865-71. [PMID: 12207018 DOI: 10.1074/jbc.m205772200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The time course of electron transfer in vitro between soluble domains of the Rieske iron-sulfur protein (ISP) and cytochrome f subunits of the cytochrome b(6)f complex of oxygenic photosynthesis was measured by stopped-flow mixing. The domains were derived from Chlamydomonas reinhardtii and expressed in Escherichia coli. The expressed 142-residue soluble ISP apoprotein was reconstituted with the [2Fe-2S] cluster. The second-order rate constant, k(2)((ISP-f)) = 1.5 x 10(6) m(-1) s(-1), for ISP to cytochrome f electron transfer was <10(-2) of the rate constant at low ionic strength, k(2)((f-PC))(> 200 x 10(6) m(-1) s(-1)), for the reduction of plastocyanin by cytochrome f, and approximately 1/30 of k(2)((f-PC)) at the ionic strength estimated for the thylakoid interior. In contrast to k(2)((f-PC)), k(2)((ISP-f)) was independent of pH and ionic strength, implying no significant role of electrostatic interactions. Effective pK values of 6.2 and 8.3, respectively, of oxidized and reduced ISP were derived from the pH dependence of the amplitude of cytochrome f reduction. The first-order rate constant, k(1)((ISP-f)), predicted from k(2)((ISP-f)) is approximately 10 and approximately 150 times smaller than the millisecond and microsecond phases of cytochrome f reduction observed in vivo. It is proposed that in the absence of electrostatic guidance, a productive docking geometry for fast electron transfer is imposed by the guided trajectory of the ISP extrinsic domain. The requirement of a specific electrically neutral docking configuration for ISP electron transfer is consistent with structure data for the related cytochrome bc(1) complex.
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Affiliation(s)
- Glenda M Soriano
- Department of Biological Sciences and Program in Biochemistry/Molecular Biology, Purdue University, West Lafayette, Indiana 47907-1392, USA
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