1
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Yang Y, An Y, Ren M, Wang H, Bai J, Du W, Kong D. The mechanisms of action of mitochondrial targeting agents in cancer: inhibiting oxidative phosphorylation and inducing apoptosis. Front Pharmacol 2023; 14:1243613. [PMID: 37954849 PMCID: PMC10635426 DOI: 10.3389/fphar.2023.1243613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Accepted: 10/12/2023] [Indexed: 11/14/2023] Open
Abstract
The tumor microenvironment affects the structure and metabolic function of mitochondria in tumor cells. This process involves changes in metabolic activity, an increase in the amount of reactive oxygen species (ROS) in tumor cells compared to normal cells, the production of more intracellular free radicals, and the activation of oxidative pathways. From a practical perspective, it is advantageous to develop drugs that target mitochondria for the treatment of malignant tumors. Such drugs can enhance the selectivity of treatments for specific cell groups, minimize toxic effects on normal tissues, and improve combinational treatments. Mitochondrial targeting agents typically rely on small molecule medications (such as synthetic small molecules agents, active ingredients of plants, mitochondrial inhibitors or autophagy inhibitors, and others), modified mitochondrial delivery system agents (such as lipophilic cation modification or combining other molecules to form targeted mitochondrial agents), and a few mitochondrial complex inhibitors. This article will review these compounds in three main areas: oxidative phosphorylation (OXPHOS), changes in ROS levels, and endogenous oxidative and apoptotic processes.
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Affiliation(s)
- Yi Yang
- Department of Pharmacy, Fourth Hospital of Hebei Medical University, Shijiazhuang, China
| | - Yahui An
- Department of Pharmacy, Fourth Hospital of Hebei Medical University, Shijiazhuang, China
| | - Mingli Ren
- Department of Pharmacy, Fourth Hospital of Hebei Medical University, Shijiazhuang, China
| | - Haijiao Wang
- Department of Pharmacy, Fourth Hospital of Hebei Medical University, Shijiazhuang, China
| | - Jing Bai
- Department of Pharmacy, Fourth Hospital of Hebei Medical University, Shijiazhuang, China
| | - Wenli Du
- Department of Pharmacy, Fourth Hospital of Hebei Medical University, Shijiazhuang, China
| | - Dezhi Kong
- Institute of Chinese Integrative Medicine, Hebei Medical University, Shijiazhuang, China
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2
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Zdorevskyi O, Djurabekova A, Lasham J, Sharma V. Horizontal proton transfer across the antiporter-like subunits in mitochondrial respiratory complex I. Chem Sci 2023; 14:6309-6318. [PMID: 37325138 PMCID: PMC10266447 DOI: 10.1039/d3sc01427d] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Accepted: 05/09/2023] [Indexed: 06/17/2023] Open
Abstract
Respiratory complex I is a redox-driven proton pump contributing to about 40% of total proton motive force required for mitochondrial ATP generation. Recent high-resolution cryo-EM structural data revealed the positions of several water molecules in the membrane domain of the large enzyme complex. However, it remains unclear how protons flow in the membrane-bound antiporter-like subunits of complex I. Here, we performed multiscale computer simulations on high-resolution structural data to model explicit proton transfer processes in the ND2 subunit of complex I. Our results show protons can travel the entire width of antiporter-like subunits, including at the subunit-subunit interface, parallel to the membrane. We identify a previously unrecognized role of conserved tyrosine residues in catalyzing horizontal proton transfer, and that long-range electrostatic effects assist in reducing energetic barriers of proton transfer dynamics. Results from our simulations warrant a revision in several prevailing proton pumping models of respiratory complex I.
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Affiliation(s)
| | | | - Jonathan Lasham
- Department of Physics, University of Helsinki Helsinki Finland
| | - Vivek Sharma
- Department of Physics, University of Helsinki Helsinki Finland
- HiLIFE Institute of Biotechnology, University of Helsinki Helsinki Finland
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3
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Sazanov LA. From the 'black box' to 'domino effect' mechanism: what have we learned from the structures of respiratory complex I. Biochem J 2023; 480:319-333. [PMID: 36920092 PMCID: PMC10212512 DOI: 10.1042/bcj20210285] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 03/16/2023]
Abstract
My group and myself have studied respiratory complex I for almost 30 years, starting in 1994 when it was known as a L-shaped giant 'black box' of bioenergetics. First breakthrough was the X-ray structure of the peripheral arm, followed by structures of the membrane arm and finally the entire complex from Thermus thermophilus. The developments in cryo-EM technology allowed us to solve the first complete structure of the twice larger, ∼1 MDa mammalian enzyme in 2016. However, the mechanism coupling, over large distances, the transfer of two electrons to pumping of four protons across the membrane remained an enigma. Recently we have solved high-resolution structures of mammalian and bacterial complex I under a range of redox conditions, including catalytic turnover. This allowed us to propose a robust and universal mechanism for complex I and related protein families. Redox reactions initially drive conformational changes around the quinone cavity and a long-distance transfer of substrate protons. These set up a stage for a series of electrostatically driven proton transfers along the membrane arm ('domino effect'), eventually resulting in proton expulsion from the distal antiporter-like subunit. The mechanism radically differs from previous suggestions, however, it naturally explains all the unusual structural features of complex I. In this review I discuss the state of knowledge on complex I, including the current most controversial issues.
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Affiliation(s)
- Leonid A. Sazanov
- Institute of Science and Technology Austria, Am Campus 1, Klosterneuburg 3400, Austria
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4
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Wikström M, Djurabekova A, Sharma V. On the role of ubiquinone in the proton translocation mechanism of respiratory complex I. FEBS Lett 2023; 597:224-236. [PMID: 36180980 DOI: 10.1002/1873-3468.14506] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 09/23/2022] [Accepted: 09/23/2022] [Indexed: 01/26/2023]
Abstract
Complex I converts oxidoreduction energy into a proton electrochemical gradient across the inner mitochondrial or bacterial cell membrane. This gradient is the primary source of energy for aerobic synthesis of ATP. Oxidation of reduced nicotinamide adenine dinucleotide (NADH) by ubiquinone (Q) yields NAD+ and ubiquinol (QH2 ), which is tightly coupled to translocation of four protons from the negatively to the positively charged side of the membrane. Electrons from NADH oxidation reach the iron-sulfur centre N2 positioned near the bottom of a tunnel that extends circa 30 Å from the membrane domain into the hydrophilic domain of the complex. The tunnel is occupied by ubiquinone, which can take a distal position near the N2 centre or proximal positions closer to the membrane. Here, we review important structural, kinetic and thermodynamic properties of ubiquinone that define its role in complex I function. We suggest that this function exceeds that of a mere substrate or electron acceptor and propose that ubiquinone may be the redox element of complex I coupling electron transfer to proton translocation.
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Affiliation(s)
- Mårten Wikström
- HiLIFE Institute of Biotechnology, University of Helsinki, Finland
| | | | - Vivek Sharma
- HiLIFE Institute of Biotechnology, University of Helsinki, Finland.,Department of Physics, University of Helsinki, Finland
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5
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Kampjut D, Sazanov LA. Structure of respiratory complex I – An emerging blueprint for the mechanism. Curr Opin Struct Biol 2022; 74:102350. [PMID: 35316665 PMCID: PMC7613608 DOI: 10.1016/j.sbi.2022.102350] [Citation(s) in RCA: 39] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 01/25/2022] [Accepted: 02/08/2022] [Indexed: 11/26/2022]
Abstract
Complex I is one of the major respiratory complexes, conserved from bacteria to mammals. It oxidises NADH, reduces quinone and pumps protons across the membrane, thus playing a central role in the oxidative energy metabolism. In this review we discuss our current state of understanding the structure of complex I from various species of mammals, plants, fungi, and bacteria, as well as of several complex I-related proteins. By comparing the structural evidence from these systems in different redox states and data from mutagenesis and molecular simulations, we formulate the mechanisms of electron transfer and proton pumping and explain how they are conformationally and electrostatically coupled. Finally, we discuss the structural basis of the deactivation phenomenon in mammalian complex I.
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6
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Djurabekova A, Galemou Yoga E, Nyman A, Pirttikoski A, Zickermann V, Haapanen O, Sharma V. Docking and molecular simulations reveal a quinone binding site on the surface of respiratory complex I. FEBS Lett 2022; 596:1133-1146. [PMID: 35363885 DOI: 10.1002/1873-3468.14346] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 03/11/2022] [Accepted: 03/24/2022] [Indexed: 11/07/2022]
Abstract
The first component of the mitochondrial electron transport chain is respiratory complex I. Several high-resolution structures of complex I from different species have been resolved. However, despite these significant achievements, the mechanism of redox-coupled proton pumping remains elusive. Here, we combined atomistic docking, molecular dynamics simulations and site-directed mutagenesis on respiratory complex I from Yarrowia lipolytica to identify a quinone (Q) binding site on its surface near the horizontal amphipathic helices of ND1 and NDUFS7 subunits. The surface-bound Q makes stable interactions with conserved charged and polar residues, including the highly conserved Arg72 from the NDUFS7 subunit. The binding and dynamics of a Q molecule at the surface-binding site raises interesting possibilities about the mechanism of complex I, which are discussed.
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Affiliation(s)
| | - Etienne Galemou Yoga
- Institute of Biochemistry II, University Hospital, Goethe University, Frankfurt am Main, Germany.,Centre for Biomolecular Magnetic Resonance, Institute for Biophysical Chemistry, Goethe University, Frankfurt am Main, Germany
| | - Aino Nyman
- Department of Physics, University of Helsinki, Finland
| | | | - Volker Zickermann
- Institute of Biochemistry II, University Hospital, Goethe University, Frankfurt am Main, Germany.,Centre for Biomolecular Magnetic Resonance, Institute for Biophysical Chemistry, Goethe University, Frankfurt am Main, Germany
| | - Outi Haapanen
- Department of Physics, University of Helsinki, Finland
| | - Vivek Sharma
- Department of Physics, University of Helsinki, Finland.,HiLIFE Institute of Biotechnology, University of Helsinki, Finland
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7
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Nguyen T, Gronauer TF, Nast‐Kolb T, Sieber SA, Lang K. Substrate Profiling of Mitochondrial Caseinolytic Protease P via a Site-Specific Photocrosslinking Approach. Angew Chem Int Ed Engl 2022; 61:e202111085. [PMID: 34847623 PMCID: PMC9306725 DOI: 10.1002/anie.202111085] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Indexed: 11/17/2022]
Abstract
Approaches for profiling protease substrates are critical for defining protease functions, but remain challenging tasks. We combine genetic code expansion, photocrosslinking and proteomics to identify substrates of the mitochondrial (mt) human caseinolytic protease P (hClpP). Site-specific incorporation of the diazirine-bearing amino acid DiazK into the inner proteolytic chamber of hClpP, followed by UV-irradiation of cells, allows to covalently trap substrate proteins of hClpP and to substantiate hClpP's major involvement in maintaining overall mt homeostasis. In addition to confirming many of the previously annotated hClpP substrates, our approach adds a diverse set of new proteins to the hClpP interactome. Importantly, our workflow allows identifying substrate dynamics upon application of external cues in an unbiased manner. Identification of unique hClpP-substrate proteins upon induction of mt oxidative stress, suggests that hClpP counteracts oxidative stress by processing of proteins that are involved in respiratory chain complex synthesis and maturation as well as in catabolic pathways.
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Affiliation(s)
- Tuan‐Anh Nguyen
- Department of ChemistryGroup of Synthetic BiochemistryTechnical University of MunichLichtenbergstr. 485748GarchingGermany
| | - Thomas F. Gronauer
- Center for Protein Assemblies (CPA)Department of ChemistryChair of Organic Chemistry IITechnical University of MunichLichtenbergstr. 485748GarchingGermany
| | - Timon Nast‐Kolb
- Center for Protein Assemblies (CPA) and Lehrstuhl für Biophysik (E27)Physics DepartmentTechnical University of MunichLichtenbergstr. 485748GarchingGermany
| | - Stephan A. Sieber
- Center for Protein Assemblies (CPA)Department of ChemistryChair of Organic Chemistry IITechnical University of MunichLichtenbergstr. 485748GarchingGermany
| | - Kathrin Lang
- Department of ChemistryGroup of Synthetic BiochemistryTechnical University of MunichLichtenbergstr. 485748GarchingGermany
- Laboratory of Organic ChemistryDepartment of Chemistry and Applied BiosciencesChair of Chemical BiologyETH ZürichVladimir-Prelog-Weg 38093ZurichSwitzerland
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8
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Nguyen T, Gronauer TF, Nast‐Kolb T, Sieber SA, Lang K. Substrate Profiling of Mitochondrial Caseinolytic Protease P via a Site‐Specific Photocrosslinking Approach. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202111085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Tuan‐Anh Nguyen
- Department of Chemistry Group of Synthetic Biochemistry Technical University of Munich Lichtenbergstr. 4 85748 Garching Germany
| | - Thomas F. Gronauer
- Center for Protein Assemblies (CPA) Department of Chemistry Chair of Organic Chemistry II Technical University of Munich Lichtenbergstr. 4 85748 Garching Germany
| | - Timon Nast‐Kolb
- Center for Protein Assemblies (CPA) and Lehrstuhl für Biophysik (E27) Physics Department Technical University of Munich Lichtenbergstr. 4 85748 Garching Germany
| | - Stephan A. Sieber
- Center for Protein Assemblies (CPA) Department of Chemistry Chair of Organic Chemistry II Technical University of Munich Lichtenbergstr. 4 85748 Garching Germany
| | - Kathrin Lang
- Department of Chemistry Group of Synthetic Biochemistry Technical University of Munich Lichtenbergstr. 4 85748 Garching Germany
- Laboratory of Organic Chemistry Department of Chemistry and Applied Biosciences Chair of Chemical Biology ETH Zürich Vladimir-Prelog-Weg 3 8093 Zurich Switzerland
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9
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Parey K, Lasham J, Mills DJ, Djurabekova A, Haapanen O, Yoga EG, Xie H, Kühlbrandt W, Sharma V, Vonck J, Zickermann V. High-resolution structure and dynamics of mitochondrial complex I-Insights into the proton pumping mechanism. SCIENCE ADVANCES 2021; 7:eabj3221. [PMID: 34767441 PMCID: PMC8589321 DOI: 10.1126/sciadv.abj3221] [Citation(s) in RCA: 65] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 09/24/2021] [Indexed: 05/23/2023]
Abstract
Mitochondrial NADH:ubiquinone oxidoreductase (complex I) is a 1-MDa membrane protein complex with a central role in energy metabolism. Redox-driven proton translocation by complex I contributes substantially to the proton motive force that drives ATP synthase. Several structures of complex I from bacteria and mitochondria have been determined, but its catalytic mechanism has remained controversial. We here present the cryo-EM structure of complex I from Yarrowia lipolytica at 2.1-Å resolution, which reveals the positions of more than 1600 protein-bound water molecules, of which ~100 are located in putative proton translocation pathways. Another structure of the same complex under steady-state activity conditions at 3.4-Å resolution indicates conformational transitions that we associate with proton injection into the central hydrophilic axis. By combining high-resolution structural data with site-directed mutagenesis and large-scale molecular dynamic simulations, we define details of the proton translocation pathways and offer insights into the redox-coupled proton pumping mechanism of complex I.
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Affiliation(s)
- Kristian Parey
- Institute of Biochemistry II, University Hospital, Goethe University, 60590 Frankfurt am Main, Germany
- Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
- Centre for Biomolecular Magnetic Resonance, Institute for Biophysical Chemistry, Goethe University, 60438 Frankfurt am Main, Germany
| | - Jonathan Lasham
- Department of Physics, University of Helsinki, 00014 Helsinki, Finland
| | - Deryck J. Mills
- Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Amina Djurabekova
- Department of Physics, University of Helsinki, 00014 Helsinki, Finland
| | - Outi Haapanen
- Department of Physics, University of Helsinki, 00014 Helsinki, Finland
| | - Etienne Galemou Yoga
- Institute of Biochemistry II, University Hospital, Goethe University, 60590 Frankfurt am Main, Germany
- Centre for Biomolecular Magnetic Resonance, Institute for Biophysical Chemistry, Goethe University, 60438 Frankfurt am Main, Germany
| | - Hao Xie
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Werner Kühlbrandt
- Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Vivek Sharma
- Department of Physics, University of Helsinki, 00014 Helsinki, Finland
- HiLIFE Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - Janet Vonck
- Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Volker Zickermann
- Institute of Biochemistry II, University Hospital, Goethe University, 60590 Frankfurt am Main, Germany
- Centre for Biomolecular Magnetic Resonance, Institute for Biophysical Chemistry, Goethe University, 60438 Frankfurt am Main, Germany
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10
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Kaur D, Khaniya U, Zhang Y, Gunner MR. Protein Motifs for Proton Transfers That Build the Transmembrane Proton Gradient. Front Chem 2021; 9:660954. [PMID: 34211960 PMCID: PMC8239185 DOI: 10.3389/fchem.2021.660954] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Accepted: 05/31/2021] [Indexed: 11/13/2022] Open
Abstract
Biological membranes are barriers to polar molecules, so membrane embedded proteins control the transfers between cellular compartments. Protein controlled transport moves substrates and activates cellular signaling cascades. In addition, the electrochemical gradient across mitochondrial, bacterial and chloroplast membranes, is a key source of stored cellular energy. This is generated by electron, proton and ion transfers through proteins. The gradient is used to fuel ATP synthesis and to drive active transport. Here the mechanisms by which protons move into the buried active sites of Photosystem II (PSII), bacterial RCs (bRCs) and through the proton pumps, Bacteriorhodopsin (bR), Complex I and Cytochrome c oxidase (CcO), are reviewed. These proteins all use water filled proton transfer paths. The proton pumps, that move protons uphill from low to high concentration compartments, also utilize Proton Loading Sites (PLS), that transiently load and unload protons and gates, which block backflow of protons. PLS and gates should be synchronized so PLS proton affinity is high when the gate opens to the side with few protons and low when the path is open to the high concentration side. Proton transfer paths in the proteins we describe have different design features. Linear paths are seen with a unique entry and exit and a relatively straight path between them. Alternatively, paths can be complex with a tangle of possible routes. Likewise, PLS can be a single residue that changes protonation state or a cluster of residues with multiple charge and tautomer states.
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Affiliation(s)
- Divya Kaur
- Department of Chemistry, The Graduate Center, City University of New York, New York, NY, United States.,Department of Physics, City College of New York, New York, NY, United States
| | - Umesh Khaniya
- Department of Physics, City College of New York, New York, NY, United States.,Department of Physics, The Graduate Center, City University of New York, New York, NY, United States
| | - Yingying Zhang
- Department of Physics, City College of New York, New York, NY, United States.,Department of Physics, The Graduate Center, City University of New York, New York, NY, United States
| | - M R Gunner
- Department of Chemistry, The Graduate Center, City University of New York, New York, NY, United States.,Department of Physics, City College of New York, New York, NY, United States.,Department of Physics, The Graduate Center, City University of New York, New York, NY, United States
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11
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Vanoni MA. Iron-sulfur flavoenzymes: the added value of making the most ancient redox cofactors and the versatile flavins work together. Open Biol 2021; 11:210010. [PMID: 33947244 PMCID: PMC8097209 DOI: 10.1098/rsob.210010] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Iron-sulfur (Fe-S) flavoproteins form a broad and growing class of complex, multi-domain and often multi-subunit proteins coupling the most ancient cofactors (the Fe-S clusters) and the most versatile coenzymes (the flavin coenzymes, FMN and FAD). These enzymes catalyse oxidoreduction reactions usually acting as switches between donors of electron pairs and acceptors of single electrons, and vice versa. Through selected examples, the enzymes' structure−function relationships with respect to rate and directionality of the electron transfer steps, the role of the apoprotein and its dynamics in modulating the electron transfer process will be discussed.
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Affiliation(s)
- Maria Antonietta Vanoni
- Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy
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12
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Essential role of accessory subunit LYRM6 in the mechanism of mitochondrial complex I. Nat Commun 2020; 11:6008. [PMID: 33243981 PMCID: PMC7693276 DOI: 10.1038/s41467-020-19778-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 10/29/2020] [Indexed: 01/18/2023] Open
Abstract
Respiratory complex I catalyzes electron transfer from NADH to ubiquinone (Q) coupled to vectorial proton translocation across the inner mitochondrial membrane. Despite recent progress in structure determination of this very large membrane protein complex, the coupling mechanism is a matter of ongoing debate and the function of accessory subunits surrounding the canonical core subunits is essentially unknown. Concerted rearrangements within a cluster of conserved loops of central subunits NDUFS2 (β1-β2S2 loop), ND1 (TMH5-6ND1 loop) and ND3 (TMH1-2ND3 loop) were suggested to be critical for its proton pumping mechanism. Here, we show that stabilization of the TMH1-2ND3 loop by accessory subunit LYRM6 (NDUFA6) is pivotal for energy conversion by mitochondrial complex I. We determined the high-resolution structure of inactive mutant F89ALYRM6 of eukaryotic complex I from the yeast Yarrowia lipolytica and found long-range structural changes affecting the entire loop cluster. In atomistic molecular dynamics simulations of the mutant, we observed conformational transitions in the loop cluster that disrupted a putative pathway for delivery of substrate protons required in Q redox chemistry. Our results elucidate in detail the essential role of accessory subunit LYRM6 for the function of eukaryotic complex I and offer clues on its redox-linked proton pumping mechanism. Respiratory complex I plays a key role in energy metabolism. Cryo-EM structure of a mutant accessory subunit LYRM6 from the yeast Yarrowia lipolytica and molecular dynamics simulations reveal conformational changes at the interface between LYRM6 and subunit ND3, propagated further into the complex. These findings offer insight into the mechanism of proton pumping by respiratory complex I.
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13
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Wang P, Dhananjayan N, Hagras MA, Stuchebrukhov AA. Respiratory complex I: Bottleneck at the entrance of quinone site requires conformational change for its opening. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1862:148326. [PMID: 33045211 DOI: 10.1016/j.bbabio.2020.148326] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Revised: 10/04/2020] [Accepted: 10/06/2020] [Indexed: 12/13/2022]
Abstract
The structure of the entire respiratory complex I is now known at reasonably high resolution for many species - bacteria, yeast, and several mammals, including human. The structure reveals an almost 30 angstrom tunnel-like chamber for ubiquinone binding in the core part of the enzyme, at the joint between the membrane and hydrophilic arms of the enzyme. Here we characterize the geometric bottleneck forming the entrance of the quinone reaction chamber. Computer simulations of quinone/quinol passage through the bottleneck suggest that in all structures available, from bacterial to human, this bottleneck is too narrow for the quinone or quinol to pass and that a conformational change is required to open the channel. Moreover, the bottleneck is too narrow even for isoprenoid tail free passage. The closed structure can be an artifact of the crystallization packing forces, low temperature, or other unnatural conditions occurring in the structural data acquisition procedure that affect this flexible part of the enzyme. Two of the helices forming the bottleneck are in direct contact with the subunit (ND3) that was recently demonstrated to be involved in conformational changes during the redox proton pumping cycle, which indicates flexibility of that part of the enzyme. We conclude that the published structures are all locked in the unfunctional states and do not represent correctly the functional enzyme; we discuss possible ways to open the structure in the context of possible mechanisms of the enzyme.
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Affiliation(s)
- Panyue Wang
- Department of Chemistry, University of California at Davis, One Shields Avenue, Davis, CA 95616, United States of America
| | - Nithin Dhananjayan
- Department of Chemistry, University of California at Davis, One Shields Avenue, Davis, CA 95616, United States of America
| | - Muhammad A Hagras
- Department of Chemistry, University of California at Davis, One Shields Avenue, Davis, CA 95616, United States of America
| | - Alexei A Stuchebrukhov
- Department of Chemistry, University of California at Davis, One Shields Avenue, Davis, CA 95616, United States of America.
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14
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Kampjut D, Sazanov LA. The coupling mechanism of mammalian respiratory complex I. Science 2020; 370:science.abc4209. [PMID: 32972993 DOI: 10.1126/science.abc4209] [Citation(s) in RCA: 149] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Accepted: 09/08/2020] [Indexed: 12/16/2022]
Abstract
Mitochondrial complex I couples NADH:ubiquinone oxidoreduction to proton pumping by an unknown mechanism. Here, we present cryo-electron microscopy structures of ovine complex I in five different conditions, including turnover, at resolutions up to 2.3 to 2.5 angstroms. Resolved water molecules allowed us to experimentally define the proton translocation pathways. Quinone binds at three positions along the quinone cavity, as does the inhibitor rotenone that also binds within subunit ND4. Dramatic conformational changes around the quinone cavity couple the redox reaction to proton translocation during open-to-closed state transitions of the enzyme. In the induced deactive state, the open conformation is arrested by the ND6 subunit. We propose a detailed molecular coupling mechanism of complex I, which is an unexpected combination of conformational changes and electrostatic interactions.
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Affiliation(s)
- Domen Kampjut
- IST Austria, Am Campus 1, 3400 Klosterneuburg, Austria
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15
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Gutiérrez-Fernández J, Kaszuba K, Minhas GS, Baradaran R, Tambalo M, Gallagher DT, Sazanov LA. Key role of quinone in the mechanism of respiratory complex I. Nat Commun 2020; 11:4135. [PMID: 32811817 PMCID: PMC7434922 DOI: 10.1038/s41467-020-17957-0] [Citation(s) in RCA: 62] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Accepted: 07/28/2020] [Indexed: 01/12/2023] Open
Abstract
Complex I is the first and the largest enzyme of respiratory chains in bacteria and mitochondria. The mechanism which couples spatially separated transfer of electrons to proton translocation in complex I is not known. Here we report five crystal structures of T. thermophilus enzyme in complex with NADH or quinone-like compounds. We also determined cryo-EM structures of major and minor native states of the complex, differing in the position of the peripheral arm. Crystal structures show that binding of quinone-like compounds (but not of NADH) leads to a related global conformational change, accompanied by local re-arrangements propagating from the quinone site to the nearest proton channel. Normal mode and molecular dynamics analyses indicate that these are likely to represent the first steps in the proton translocation mechanism. Our results suggest that quinone binding and chemistry play a key role in the coupling mechanism of complex I. Complex I (NADH:ubiquinone oxidoreductase) is the first enzyme of the respiratory chain in bacteria and mitochondria. Here, the authors present cryo-EM and crystal structures of T. thermophilus complex I in different conformational states and further analyse them by Normal Mode Analysis and molecular dynamics simulations and conclude that quinone redox reactions are important for the coupling mechanism of complex I.
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Affiliation(s)
| | - Karol Kaszuba
- Institute of Science and Technology Austria, Am Campus 1, A-3400, Klosterneuburg, Austria
| | - Gurdeep S Minhas
- Medical Research Council Mitochondrial Biology Unit, Keith Peters Building, Hills rd, Cambridge, CB2 0XY, UK.,Sosei Heptares, Steinmetz Building, Granta Park, Cambridge, CB21 6DG, UK
| | - Rozbeh Baradaran
- Medical Research Council Mitochondrial Biology Unit, Keith Peters Building, Hills rd, Cambridge, CB2 0XY, UK.,Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, 17165, Solna, Sweden
| | - Margherita Tambalo
- Institute of Science and Technology Austria, Am Campus 1, A-3400, Klosterneuburg, Austria
| | - David T Gallagher
- Medical Research Council Mitochondrial Biology Unit, Keith Peters Building, Hills rd, Cambridge, CB2 0XY, UK
| | - Leonid A Sazanov
- Institute of Science and Technology Austria, Am Campus 1, A-3400, Klosterneuburg, Austria.
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16
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Haapanen O, Reidelbach M, Sharma V. Coupling of quinone dynamics to proton pumping in respiratory complex I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1861:148287. [PMID: 32777307 DOI: 10.1016/j.bbabio.2020.148287] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 07/09/2020] [Accepted: 08/03/2020] [Indexed: 12/12/2022]
Abstract
Respiratory complex I (NADH:quinone oxidoreductase) plays a central role in generating the proton electrochemical gradient in mitochondrial and bacterial membranes, which is needed to generate ATP. Several high-resolution structures of complex I have been determined, revealing its intricate architecture and complementing the biochemical and biophysical studies. However, the molecular mechanism of long-range coupling between ubiquinone (Q) reduction and proton pumping is not known. Computer simulations have been applied to decipher the dynamics of Q molecule in the ~30 Å long Q tunnel. In this short report, we discuss the binding and dynamics of Q at computationally predicted Q binding sites, many of which are supported by structural data on complex I. We suggest that the binding of Q at these sites is coupled to proton pumping by means of conformational rearrangements in the conserved loops of core subunits.
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Affiliation(s)
- Outi Haapanen
- Department of Physics, University of Helsinki, Finland
| | | | - Vivek Sharma
- Department of Physics, University of Helsinki, Finland; HiLIFE Institute of Biotechnology, University of Helsinki, Finland.
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17
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Lin Y, Xu X, Zhao D, Liu F, Luo Y, Du J, Wang D, Ji K, Zhao Y, Yan C. A novel m.11406 T > A mutation in mitochondrial ND4 gene causes MELAS syndrome. Mitochondrion 2020; 54:57-64. [PMID: 32659360 DOI: 10.1016/j.mito.2020.06.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 05/16/2020] [Accepted: 06/25/2020] [Indexed: 10/23/2022]
Abstract
Pathogenic point mutations of mitochondrial DNA (mtDNA) are associated with a large number of heterogeneous diseases involving multiple systems with which patients may present with a wide range of clinical phenotypes. In this study, we describe a novel heteroplasmic missense mutation, m.11406 T > A, of the ND4 gene encoding the subunit 4 of mitochondrial complex I in a 32-year-old woman with recurrent epileptic seizure, headache and bilateral hearing loss. Skeletal muscle histochemistry demonstrated that approximately 20% of fibers were cytochrome C oxidase (COX) deficient with increased activity of succinate dehydrogenase (SDH). Further investigations in muscle specimens showed significantly reduced level of ND4 protein. It is interesting that the subunits of complex I (ND1 and NDFUB8) and complex IV(CO1) were also remarkably decreased. These findings indicate that ND1, NDFUB8 and CO1 are more susceptible than other subunits to mutations in the mitochondrial ND4 gene.
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Affiliation(s)
- Yan Lin
- Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Xuebi Xu
- Department of Neurology, First Affiliated Hospital of Wenzhou Medical University, Nanbaixiang Street, Ouhai District, Wenzhou 325000, China
| | - Dandan Zhao
- Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Fuchen Liu
- Department of Neurobiology, Yale University School of Medicine, New Haven, CT 06511, USA
| | - Yuebei Luo
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China
| | - Jixiang Du
- Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Dongdong Wang
- Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Kunqian Ji
- Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250012, China.
| | - Yuying Zhao
- Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Chuanzhu Yan
- Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250012, China; Mitochondrial Medicine Laboratory, Qilu Hospital (Qingdao), Shandong University, Qingdao, Shandong 266035, China; Brain Science Research Institute, Shandong University, Jinan, Shandong 250012, China.
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18
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Parey K, Wirth C, Vonck J, Zickermann V. Respiratory complex I - structure, mechanism and evolution. Curr Opin Struct Biol 2020; 63:1-9. [PMID: 32058886 DOI: 10.1016/j.sbi.2020.01.004] [Citation(s) in RCA: 77] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 01/10/2020] [Indexed: 02/07/2023]
Abstract
Respiratory complex I is an intricate multi-subunit membrane protein with a central function in aerobic energy metabolism. During the last years, structures of mitochondrial complex I and respiratory supercomplexes were determined by cryo-EM at increasing resolution. Structural and computational studies have shed light on the dynamics of proton translocation pathways, the interaction of complex I with lipids and the unusual access pathway of ubiquinone to the active site. Recent advances in understanding complex I function include characterization of specific conformational changes that are critical for proton pumping. Cryo-EM structures of the NADH dehydrogenase-like (NDH) complex of photosynthesis and a bacterial membrane bound hydrogenase (MBH) have provided a broader perspective on the complex I superfamily.
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Affiliation(s)
- Kristian Parey
- Institute of Biochemistry II, University Hospital, Goethe University, Frankfurt am Main, Germany; Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany; Centre for Biomolecular Magnetic Resonance, Institute for Biophysical Chemistry, Goethe University, Frankfurt am Main, Germany
| | - Christophe Wirth
- Institute of Biochemistry and Molecular Biology, ZBMZ, Medical Faculty, Albert-Ludwigs-University Freiburg, Freiburg, Germany
| | - Janet Vonck
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
| | - Volker Zickermann
- Institute of Biochemistry II, University Hospital, Goethe University, Frankfurt am Main, Germany; Centre for Biomolecular Magnetic Resonance, Institute for Biophysical Chemistry, Goethe University, Frankfurt am Main, Germany.
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19
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Respiratory complex I - Mechanistic insights and advances in structure determination. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1861:148153. [PMID: 31935361 DOI: 10.1016/j.bbabio.2020.148153] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Revised: 12/16/2019] [Accepted: 01/08/2020] [Indexed: 12/17/2022]
Abstract
Complex I is the largest and most intricate redox-driven proton pump of the respiratory chain. The structure of bacterial and mitochondrial complex I has been determined by X-ray crystallography and cryo-EM at increasing resolution. The recent cryo-EM structures of the complex I-like NDH complex and membrane bound hydrogenase open a new and more comprehensive perspective on the complex I superfamily. Functional studies and molecular modeling approaches have greatly advanced our understanding of the catalytic cycle of complex I. However, the molecular mechanism by which energy is extracted from the redox reaction and utilized to drive proton translocation is unresolved and a matter of ongoing debate. Here, we review progress in structure determination and functional characterization of complex I and discuss current mechanistic models.
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20
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Abstract
Complexes I to IV, with the exception of Complex II, are redox-driven proton pumps that convert redox energy of oxygen reduction to proton gradient across the mitochondrial or bacterial membrane; in turn, the created electrochemical gradient drives the adenosine triphosphate synthesis in the cells by utilizing complex V of the chain. Here we address a general question of the efficiency of such enzymes, considering them as molecular machines that couple endergonic and exergonic reactions and converting one form of free energy into another. One well-known example of the efficiency is given by Carnot's theorem for heat engines. Here we extend the concept to respiratory enzymes and specifically focus on the proton pumping by Complex I of the respiratory chain, nicotinamide adenine dinucleotide dehydrogenase. To discuss the efficiency issues, we develop a model of enzyme kinetics, which generalizes the Michaelis-Menten model. Our model includes several substrates and products and, in general, can be considered as Generalized Michaelis-Menten Kinetic model. The model might be useful for describing complex enzyme kinetics, regardless of the efficiency issues that are addressed in this paper.
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Affiliation(s)
- Alexei A Stuchebrukhov
- Department of Chemistry , University of California at Davis , Davis , California 95616 , United States
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21
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Mutations in a conserved loop in the PSST subunit of respiratory complex I affect ubiquinone binding and dynamics. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:573-581. [PMID: 31226318 DOI: 10.1016/j.bbabio.2019.06.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Revised: 05/10/2019] [Accepted: 06/15/2019] [Indexed: 12/13/2022]
Abstract
Respiratory complex I catalyses the reduction of ubiquinone (Q) from NADH coupled to proton pumping across the inner membrane of mitochondria. The electrical charging of the inner mitochondrial membrane drives the synthesis of ATP, which is used to power biochemical reactions of the cell. The recent surge in structural data on complex I from bacteria and mitochondria have contributed to significant understanding of its molecular architecture. However, despite these accomplishments, the role of various subdomains in redox-coupled proton pumping remains entirely unclear. In this work, we have mutated conserved residues in the loop of the PSST subunit that faces the ~30 Å long unique Q-binding tunnel of respiratory complex I. The data show a drastic decrease in Q reductase activity upon mutating several residues despite full assembly of the complex. In-silico modeling and multiple microsecond long molecular dynamics simulations of wild-type and enzyme variants with exchanges of conserved arginine residues revealed remarkable ejection of the bound Q from the site near terminal electron donor N2. Based on experiments and long-time scale molecular simulations, we identify microscopic elements that dynamically control the diffusion of Q and are central to redox-coupled proton pumping in respiratory complex I.
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22
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Enkavi G, Javanainen M, Kulig W, Róg T, Vattulainen I. Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance. Chem Rev 2019; 119:5607-5774. [PMID: 30859819 PMCID: PMC6727218 DOI: 10.1021/acs.chemrev.8b00538] [Citation(s) in RCA: 184] [Impact Index Per Article: 36.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Indexed: 12/23/2022]
Abstract
Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.
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Affiliation(s)
- Giray Enkavi
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Matti Javanainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy
of Sciences, Flemingovo naḿesti 542/2, 16610 Prague, Czech Republic
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Waldemar Kulig
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Tomasz Róg
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Ilpo Vattulainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
- MEMPHYS-Center
for Biomembrane Physics
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23
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Haapanen O, Djurabekova A, Sharma V. Role of Second Quinone Binding Site in Proton Pumping by Respiratory Complex I. Front Chem 2019; 7:221. [PMID: 31024903 PMCID: PMC6465577 DOI: 10.3389/fchem.2019.00221] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 03/21/2019] [Indexed: 12/22/2022] Open
Abstract
Respiratory complex I performs the reduction of quinone (Q) to quinol (QH2) and pumps protons across the membrane. Structural data on complex I have provided spectacular insights into the electron and proton transfer paths, as well as into the long (~30 Å) and unique substrate binding channel. However, due to missing structural information on Q binding modes, it remains unclear how Q reduction drives long range (~20 nm) redox-coupled proton pumping in complex I. Here we applied multiscale computational approaches to study the dynamics and redox chemistry of Q and QH2. Based on tens of microseconds of atomistic molecular dynamics (MD) simulations of bacterial and mitochondrial complex I, we find that the dynamics of Q is remarkably rapid and it diffuses from the N2 binding site to another stable site near the entrance of the Q channel in microseconds. Analysis of simulation trajectories also reveal the presence of yet another Q binding site 25–30 Å from the N2 center, which is in remarkable agreement with the electron density observed in recent cryo electron microscopy structure of complex I from Yarrowia lipolytica. Quantum chemical computations on the two Q binding sites closer to the entrance of the Q tunnel reveal redox-coupled protonation reactions that may be important in driving the proton pump of complex I.
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Affiliation(s)
- Outi Haapanen
- Department of Physics, University of Helsinki, Helsinki, Finland
| | | | - Vivek Sharma
- Department of Physics, University of Helsinki, Helsinki, Finland.,Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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24
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Uno S, Kimura H, Murai M, Miyoshi H. Exploring the quinone/inhibitor-binding pocket in mitochondrial respiratory complex I by chemical biology approaches. J Biol Chem 2018; 294:679-696. [PMID: 30425100 DOI: 10.1074/jbc.ra118.006056] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Revised: 11/10/2018] [Indexed: 11/06/2022] Open
Abstract
NADH-quinone oxidoreductase (respiratory complex I) couples NADH-to-quinone electron transfer to the translocation of protons across the membrane. Even though the architecture of the quinone-access channel in the enzyme has been modeled by X-ray crystallography and cryo-EM, conflicting findings raise the question whether the models fully reflect physiologically relevant states present throughout the catalytic cycle. To gain further insights into the structural features of the binding pocket for quinone/inhibitor, we performed chemical biology experiments using bovine heart sub-mitochondrial particles. We synthesized ubiquinones that are oversized (SF-UQs) or lipid-like (PC-UQs) and are highly unlikely to enter and transit the predicted narrow channel. We found that SF-UQs and PC-UQs can be catalytically reduced by complex I, albeit only at moderate or low rates. Moreover, quinone-site inhibitors completely blocked the catalytic reduction and the membrane potential formation coupled to this reduction. Photoaffinity-labeling experiments revealed that amiloride-type inhibitors bind to the interfacial domain of multiple core subunits (49 kDa, ND1, and PSST) and the 39-kDa supernumerary subunit, although the latter does not make up the channel cavity in the current models. The binding of amilorides to the multiple target subunits was remarkably suppressed by other quinone-site inhibitors and SF-UQs. Taken together, the present results are difficult to reconcile with the current channel models. On the basis of comprehensive interpretations of the present results and of previous findings, we discuss the physiological relevance of these models.
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Affiliation(s)
- Shinpei Uno
- From the Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Hironori Kimura
- From the Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Masatoshi Murai
- From the Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Hideto Miyoshi
- From the Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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25
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Abstract
Complex I couples the free energy released from quinone (Q) reduction to pump protons across the biological membrane in the respiratory chains of mitochondria and many bacteria. The Q reduction site is separated by a large distance from the proton-pumping membrane domain. To address the molecular mechanism of this long-range proton-electron coupling, we perform here full atomistic molecular dynamics simulations, free energy calculations, and continuum electrostatics calculations on complex I from Thermus thermophilus We show that the dynamics of Q is redox-state-dependent, and that quinol, QH2, moves out of its reduction site and into a site in the Q tunnel that is occupied by a Q analog in a crystal structure of Yarrowia lipolytica We also identify a second Q-binding site near the opening of the Q tunnel in the membrane domain, where the Q headgroup forms strong interactions with a cluster of aromatic and charged residues, while the Q tail resides in the lipid membrane. We estimate the effective diffusion coefficient of Q in the tunnel, and in turn the characteristic time for Q to reach the active site and for QH2 to escape to the membrane. Our simulations show that Q moves along the Q tunnel in a redox-state-dependent manner, with distinct binding sites formed by conserved residue clusters. The motion of Q to these binding sites is proposed to be coupled to the proton-pumping machinery in complex I.
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