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Muneeswaran G, Pandiaraj M, Kartheeswaran S, Sankaralingam M, Muthukumar K, Karunakaran C. Molecular dynamics simulation approach to explore atomistic molecular mechanism of peroxidase activity of apoptotic cytochrome c mutants. INFORMATICS IN MEDICINE UNLOCKED 2018. [DOI: 10.1016/j.imu.2018.04.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
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Muneeswaran G, Kartheeswaran S, Muthukumar K, Karunakaran C. Temperature-dependent conformational dynamics of cytochrome c: Implications in apoptosis. J Mol Graph Model 2017; 79:140-148. [PMID: 29161635 DOI: 10.1016/j.jmgm.2017.10.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 10/12/2017] [Accepted: 10/12/2017] [Indexed: 11/29/2022]
Abstract
Heat, electric shock, and burn injuries induce apoptosis by releasing cytochrome c (cyt-c) from mitochondria and by subsequently activating the death protease, caspases-3. During apoptosis, cyt-c undergoes changes in the secondary structure that have been suggested to increase its peroxidase activity. Information about these structural changes will provide better understanding of the apoptotic mechanism. Hence, temperature-dependent conformational dynamics of cyt-c has been investigated through molecular dynamics (MD) simulations to explain the structural changes and to correlate them with its apoptotic behavior. We observe that, at lower temperatures (223, 248, and 300K), the secondary structure of cyt-c, remains stable, while at higher temperatures (323, 373, 423, and 473K), the secondary structural regions change significantly. Further, our MD results indicate that these structural changes are mainly localized on α-helices, turns, β-sheets, and important loops that were involved in the stabilization of the heme conformation. This conformational transition between specific regions of secondary structure of cyt-c directly affects the electron tunneling properties of the proteins as observed experimentally. We quantify and compare these changes and explain that the temperature plays a vital role in assuring the structural stability of cyt-c and thus its functions. Our findings from this MD study reproduce experimental results at high temperatures and provide evidence for the alteration of the heme through the disruption of the H-bonding interactions between specific regions of cyt-c, thereby enhancing its peroxidase activity which plays a crucial role in the apoptotic process.
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Affiliation(s)
- Gurusamy Muneeswaran
- Biomedical Research Lab, Department of Chemistry, VHNSN College (Autonomous), Virudhunagar, 626 001, Tamilnadu, India; Department of Chemistry, School of Advanced Sciences, Kalasalingam Academy of Research and Education, Krishnanakoil, 626 126, Tamil Nadu, India
| | - Subramanian Kartheeswaran
- Department of Master of Computer Applications, School of Computing, Kalasalingam Academy of Research and Education, Krishnanakoil, 626 126, Tamil Nadu, India
| | | | - Chandran Karunakaran
- Biomedical Research Lab, Department of Chemistry, VHNSN College (Autonomous), Virudhunagar, 626 001, Tamilnadu, India.
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Investigation of structural dynamics of Thrombocytopenia Cargeeg mutants of human apoptotic cytochrome c: A molecular dynamics simulation approach. Biophys Chem 2017; 230:117-126. [PMID: 28958449 DOI: 10.1016/j.bpc.2017.09.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Revised: 09/04/2017] [Accepted: 09/21/2017] [Indexed: 11/24/2022]
Abstract
Naturally occurring mutations to cytochrome c (cyt-c) have been identified recently in patients with mild autosomal dominant thrombocytopenia (low platelet levels), which yield cyt-c mutants with enhanced apoptotic activity. However, the molecular mechanism underlying this low platelet production and enhanced apoptosis remain unclear. Therefore, an attempt is made herein for the first time to investigate the effects of mutations of glycine 41 by serine (G41S) and tyrosine 48 by histidine (Y48H) on the conformational and dynamic changes of apoptotic (Fe3+) cyt-c using all atom molecular dynamics (MD) simulations in explicit water solvent. Our 30ns MD simulations demonstrate considerable structural differences in G41S and Y48H compared to wild type (WT) cyt-c, such as increasing distances between the critical electron transfer residues results in open conformation at the heme active site, large fluctuations in β-turns and α-helices. Additionally, although the β-sheets remain mostly unaffected in all the three cyt-c simulations, the α-helices undergo conformational switch to β-turns in both the mutant simulations. Importantly, this conformational switch of α-helix to β-turn around heme active site should attributes to the loss of intraprotein H-bonds in the mutant simulations especially between NE2 (His26) and O (Pro44) in agreement with the experimental report. Further, essential dynamics analysis reveals that overall motions of WT cyt-c is mainly involved only in the first eigenvector, but in G41S and Y48H the overall motions are mainly in three and two eigenvectors respectively. Overall, the detailed atomistic level information provide a unifying description for the molecular mechanism of structural destabilization, disregulation of platelet formation and enhanced peroxidase activity of the mutant cyt-c's in the pathology of intrinsic apoptosis.
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Crofts AR, Rose SW, Burton RL, Desai AV, Kenis PJA, Dikanov SA. The Q-Cycle Mechanism of the bc1 Complex: A Biologist’s Perspective on Atomistic Studies. J Phys Chem B 2017; 121:3701-3717. [DOI: 10.1021/acs.jpcb.6b10524] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Antony R. Crofts
- Department
of Biochemistry, University of Illinois at Urbana−Champaign, 419 Roger Adams Lab, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
- Center
for Biophysics and Quantitative Biology, University of Illinois at Urbana−Champaign, 179 Loomis, 1110 West Green Street, Urbana, Illinois 61801, United States
| | - Stuart W. Rose
- Center
for Biophysics and Quantitative Biology, University of Illinois at Urbana−Champaign, 179 Loomis, 1110 West Green Street, Urbana, Illinois 61801, United States
| | - Rodney L. Burton
- Department
of Biochemistry, University of Illinois at Urbana−Champaign, 419 Roger Adams Lab, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Amit V. Desai
- Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Paul J. A. Kenis
- Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Sergei A. Dikanov
- Department
of Veterinary Clinical Medicine, University of Illinois at Urbana−Champaign, 1008 West Hazelwood Drive, Urbana, Illinois 61801, United States
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Oliveira ASF, Campos SRR, Baptista AM, Soares CM. Coupling between protonation and conformation in cytochrome c oxidase: Insights from constant-pH MD simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:759-71. [PMID: 27033303 DOI: 10.1016/j.bbabio.2016.03.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 03/18/2016] [Accepted: 03/23/2016] [Indexed: 12/11/2022]
Abstract
Cytochrome c oxidases (CcOs) are the terminal enzymes of the respiratory chain in mitochondria and most bacteria. These enzymes reduce dioxygen (O(2)) to water and, simultaneously, generate a transmembrane electrochemical proton gradient. Despite their importance in the aerobic metabolism and the large amount of structural and biochemical data available for the A1-type CcO family, there is still no consensually accepted description of the molecular mechanisms operating in this protein. A substantial number of questions about the CcO's working mechanism remain to be answered, including how the protonation behavior of some key residues is modulated during a reduction cycle and how is the conformation of the protein affected by protonation. The main objective of this work was to study the protonation-conformation coupling in CcOs and identify the molecular factors that control the protonation state of some key residues. In order to directly capture the interplay between protonation and conformational effects, we have performed constant-pH MD simulations of an A1-type CcO inserted into a lipid bilayer in two redox states (oxidized and reduced) at physiological pH. From the simulations, we were able to identify several groups with unusual titration behavior that are highly dependent on the protein redox state, including the A-propionate from heme a and the D-propionate from heme a3, two key groups possibly involved in proton pumping. The protonation state of these two groups is heavily influenced by subtle conformational changes in the protein (notably of R481(I) and R482(I)) and by small changes in the hydrogen bond network.
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Affiliation(s)
- A Sofia F Oliveira
- ITQB, Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, Portugal
| | - Sara R R Campos
- ITQB, Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, Portugal
| | - António M Baptista
- ITQB, Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, Portugal.
| | - Cláudio M Soares
- ITQB, Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, Portugal.
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Molecular simulation and modeling of complex I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:915-21. [PMID: 26780586 DOI: 10.1016/j.bbabio.2016.01.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 01/06/2016] [Accepted: 01/07/2016] [Indexed: 11/23/2022]
Abstract
Molecular modeling and molecular dynamics simulations play an important role in the functional characterization of complex I. With its large size and complicated function, linking quinone reduction to proton pumping across a membrane, complex I poses unique modeling challenges. Nonetheless, simulations have already helped in the identification of possible proton transfer pathways. Simulations have also shed light on the coupling between electron and proton transfer, thus pointing the way in the search for the mechanistic principles underlying the proton pump. In addition to reviewing what has already been achieved in complex I modeling, we aim here to identify pressing issues and to provide guidance for future research to harness the power of modeling in the functional characterization of complex I. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.
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Wang B, Feig M, Cukier RI, Burton ZF. Computational simulation strategies for analysis of multisubunit RNA polymerases. Chem Rev 2013; 113:8546-66. [PMID: 23987500 PMCID: PMC3829680 DOI: 10.1021/cr400046x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Indexed: 12/13/2022]
Affiliation(s)
- Beibei Wang
- Department
of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824-1319, United States
| | - Michael Feig
- Department
of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824-1319, United States
- Department
of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Robert I. Cukier
- Department
of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Zachary F. Burton
- Department
of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824-1319, United States
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Brzezinski P, Öjemyr LN, Ädelroth P. Intermediates generated during the reaction of reduced Rhodobacter sphaeroides cytochrome c oxidase with dioxygen. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:843-7. [DOI: 10.1016/j.bbabio.2013.04.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 04/18/2013] [Accepted: 04/23/2013] [Indexed: 10/26/2022]
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Low-temperature molecular dynamics simulations of horse heart cytochrome c and comparison with inelastic neutron scattering data. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2012; 42:291-300. [DOI: 10.1007/s00249-012-0874-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 11/07/2012] [Accepted: 11/16/2012] [Indexed: 11/26/2022]
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Chen D, Wei GW. Quantum dynamics in continuum for proton transport--generalized correlation. J Chem Phys 2012; 136:134109. [PMID: 22482542 DOI: 10.1063/1.3698598] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
As a key process of many biological reactions such as biological energy transduction or human sensory systems, proton transport has attracted much research attention in biological, biophysical, and mathematical fields. A quantum dynamics in continuum framework has been proposed to study proton permeation through membrane proteins in our earlier work and the present work focuses on the generalized correlation of protons with their environment. Being complementary to electrostatic potentials, generalized correlations consist of proton-proton, proton-ion, proton-protein, and proton-water interactions. In our approach, protons are treated as quantum particles while other components of generalized correlations are described classically and in different levels of approximations upon simulation feasibility and difficulty. Specifically, the membrane protein is modeled as a group of discrete atoms, while ion densities are approximated by Boltzmann distributions, and water molecules are represented as a dielectric continuum. These proton-environment interactions are formulated as convolutions between number densities of species and their corresponding interaction kernels, in which parameters are obtained from experimental data. In the present formulation, generalized correlations are important components in the total Hamiltonian of protons, and thus is seamlessly embedded in the multiscale/multiphysics total variational model of the system. It takes care of non-electrostatic interactions, including the finite size effect, the geometry confinement induced channel barriers, dehydration and hydrogen bond effects, etc. The variational principle or the Euler-Lagrange equation is utilized to minimize the total energy functional, which includes the total Hamiltonian of protons, and obtain a new version of generalized Laplace-Beltrami equation, generalized Poisson-Boltzmann equation and generalized Kohn-Sham equation. A set of numerical algorithms, such as the matched interface and boundary method, the Dirichlet to Neumann mapping, Gummel iteration, and Krylov space techniques, is employed to improve the accuracy, efficiency, and robustness of model simulations. Finally, comparisons between the present model predictions and experimental data of current-voltage curves, as well as current-concentration curves of the Gramicidin A channel, verify our new model.
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Affiliation(s)
- Duan Chen
- Department of Mathematics, Michigan State University, East Lansing, Michigan 48824, USA
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Peng Y, Voth GA. Expanding the view of proton pumping in cytochrome c oxidase through computer simulation. BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1817:518-25. [PMID: 22178790 PMCID: PMC4120846 DOI: 10.1016/j.bbabio.2011.11.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2011] [Revised: 11/23/2011] [Accepted: 11/24/2011] [Indexed: 01/01/2023]
Abstract
In cytochrome c oxidase (CcO), a redox-driven proton pump, protons are transported by the Grotthuss shuttling via hydrogen-bonded water molecules and protonatable residues. Proton transport through the D-pathway is a complicated process that is highly sensitive to alterations in the amino acids or the solvation structure in the channel, both of which can inhibit proton pumping and enzymatic activity. Simulations of proton transport in the hydrophobic cavity showed a clear redox state dependence. To study the mechanism of proton pumping in CcO, multi-state empirical valence bond (MS-EVB) simulations have been conducted, focusing on the proton transport through the D-pathway and the hydrophobic cavity next to the binuclear center. The hydration structures, transport pathways, effects of residues, and free energy surfaces of proton transport were revealed in these MS-EVB simulations. The mechanistic insight gained from them is herein reviewed and placed in context for future studies.
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Affiliation(s)
- Yuxing Peng
- Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, and Computation Institute, University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, USA
| | - Gregory A. Voth
- Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, and Computation Institute, University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, USA
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Varanasi L, Hosler JP. Subunit III-depleted cytochrome c oxidase provides insight into the process of proton uptake by proteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:545-51. [PMID: 22023935 DOI: 10.1016/j.bbabio.2011.10.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Revised: 10/10/2011] [Accepted: 10/10/2011] [Indexed: 11/30/2022]
Abstract
We review studies of subunit III-depleted cytochrome c oxidase (CcO III (-)) that elucidate the structural basis of steady-state proton uptake from solvent into an internal proton transfer pathway. The removal of subunit III from R. sphaeroides CcO makes proton uptake into the D pathway a rate-determining step, such that measurements of the pH dependence of steady-state O(2) consumption can be used to compare the rate and functional pK(a) of proton uptake by D pathways containing different initial proton acceptors. The removal of subunit III also promotes spontaneous suicide inactivation by CcO, greatly shortening its catalytic lifespan. Because the probability of suicide inactivation is controlled by the rate at which the D pathway delivers protons to the active site, measurements of catalytic lifespan provide a second method to compare the relative efficacy of proton uptake by engineered CcO III (-) forms. These simple experimental systems have been used to explore general questions of proton uptake by proteins, such as the functional value of an initial proton acceptor, whether an initial acceptor must be surface-exposed, which side chains will function as initial proton acceptors and whether multiple acceptors can speed proton uptake.
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Affiliation(s)
- Lakshman Varanasi
- Department of Biochemistry, The University of Mississippi Medical Center, Jackson, MS, USA.
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Crystallographic and online spectral evidence for role of conformational change and conserved water in cytochrome oxidase proton pump. Proc Natl Acad Sci U S A 2011; 108:1284-9. [PMID: 21205904 DOI: 10.1073/pnas.1012846108] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Crystal structures in both oxidized and reduced forms are reported for two bacterial cytochrome c oxidase mutants that define the D and K proton paths, showing conformational change in response to reduction and the loss of strategic waters that can account for inhibition of proton transfer. In the oxidized state both mutants of the Rhodobacter sphaeroides enzyme, D132A and K362M, show overall structures similar to wild type, indicating no long-range effects of mutation. In the reduced state, the mutants show an altered conformation similar to that seen in reduced wild type, confirming this reproducible, reversible response to reduction. In the strongly inhibited D132A mutant, positions of residues and waters in the D pathway are unaffected except in the entry region close to the mutation, where a chloride ion replaces the missing carboxyl and a 2-Å shift in N207 results in loss of its associated water. In K362M, the methionine occupies the same position as the original lysine, but K362- and T359-associated waters in the wild-type structure are missing, likely accounting for the severe inhibition. Spectra of oxidized frozen crystals taken during X-ray radiation show metal center reduction, but indicate development of a strained configuration that only relaxes to a native form upon annealing. Resistance of the frozen crystal to structural change clarifies why the oxidized conformation is observable and supports the conclusion that the reduced conformation has functional significance. A mechanism is described that explains the conformational change and the incomplete response of the D-path mutant.
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Shepherd LMS, Morrison CA. Simulating proton transport through a simplified model for trans-membrane proteins. J Phys Chem B 2010; 114:7047-55. [PMID: 20455530 DOI: 10.1021/jp910262d] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Ab initio MD simulations on a polyglycine helix and water-wire expressed under periodic boundary conditions have created a channel that supports proton transfer up to distances of 10.5 A. The effect of varying the density of water molecules in the channel has been investigated. A range of cationic states are identified with widely varying lifetimes. The mechanism of proton transport in this model shares some features with the simulations reported for bulk water, with, e.g., the hydrogen bond distance shortening in the time period leading up to successful proton transfer. However, there are also some important differences such as the observation of a heightened number of proton rattling events. We also observe that the helix plays an important role in directing the behavior of the water wire: the most active proton transport regions of the water-wire are found in areas where the helix is most tightly coiled. Finally, we report on the effects of different DFT functionals to model a water-wire and on the importance of including dispersion corrections to stabilize the alpha-helical structure.
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Affiliation(s)
- Lynsey M S Shepherd
- School of Chemistry and EaSTCHEM Research School, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh, EH9 3JJ, UK
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Sugitani R, Stuchebrukhov AA. Molecular dynamics simulation of water in cytochrome c oxidase reveals two water exit pathways and the mechanism of transport. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:1140-50. [PMID: 19393218 DOI: 10.1016/j.bbabio.2009.04.004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Revised: 04/09/2009] [Accepted: 04/14/2009] [Indexed: 10/20/2022]
Abstract
We have examined the network of connected internal cavities in cytochrome c oxidase along which water produced at the catalytic center is removed from the enzyme. Using combination of structural analysis, molecular dynamics simulations, and free energy calculations we have identified two exit pathways that connect the Mg2+ ion cavity to the outside of the enzyme. Each pathway has a well-defined bottleneck, which determines the overall rate of water traffic along the exit pathway, and a specific cooperative mechanism of passing it. One of the pathways is going via Arg438/439 (in bovine numbering) toward the CuA center, approaching closely its His204B ligand and Lys171B residue; and the other is going toward Asp364 and Thr294. Comparison of the pathways among different aa3-type enzymes shows that they are well conserved. Possible connections of the finding to redox-coupled proton pumping mechanism are discussed. We propose specific mutations near the bottlenecks of the exit pathways that can test some of our hypotheses.
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Affiliation(s)
- Ryogo Sugitani
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA 95616, USA
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Dürr KL, Koepke J, Hellwig P, Müller H, Angerer H, Peng G, Olkhova E, Richter OMH, Ludwig B, Michel H. A D-Pathway Mutation Decouples the Paracoccus denitrificans Cytochrome c Oxidase by Altering the Side-Chain Orientation of a Distant Conserved Glutamate. J Mol Biol 2008; 384:865-77. [DOI: 10.1016/j.jmb.2008.09.074] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 08/28/2008] [Accepted: 09/17/2008] [Indexed: 11/16/2022]
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Ho FM. Uncovering channels in photosystem II by computer modelling: current progress, future prospects, and lessons from analogous systems. PHOTOSYNTHESIS RESEARCH 2008; 98:503-522. [PMID: 18798008 DOI: 10.1007/s11120-008-9358-2] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Accepted: 08/18/2008] [Indexed: 05/26/2023]
Abstract
Even prior to the publication of the crystal structures for photosystem II (PSII), it had already been suggested that water, O(2) and H(+) channels exist in PSII to achieve directed transport of these molecules, and to avoid undesirable side reactions. Computational efforts to uncover these channels and investigate their properties are still at early stages, and have so far only been based on the static PSII structure. The rationale behind the proposals for such channels and the computer modelling studies thus far are reviewed here. The need to take the dynamic protein into account is then highlighted with reference to the specific issues and techniques applicable to the simulation of each of the three channels. In particular, lessons are drawn from simulation studies on other protein systems containing similar channels.
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Affiliation(s)
- Felix M Ho
- Department of Photochemistry and Molecular Science, The Angström Laboratory, Uppsala University, Uppsala, Sweden.
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Glutamic acid 242 is a valve in the proton pump of cytochrome c oxidase. Proc Natl Acad Sci U S A 2008; 105:6255-9. [PMID: 18430799 DOI: 10.1073/pnas.0800770105] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Aerobic life is based on a molecular machinery that utilizes oxygen as a terminal electron sink. The membrane-bound cytochrome c oxidase (CcO) catalyzes the reduction of oxygen to water in mitochondria and many bacteria. The energy released in this reaction is conserved by pumping protons across the mitochondrial or bacterial membrane, creating an electrochemical proton gradient that drives production of ATP. A crucial question is how the protons pumped by CcO are prevented from flowing backwards during the process. Here, we show by molecular dynamics simulations that the conserved glutamic acid 242 near the active site of CcO undergoes a protonation state-dependent conformational change, which provides a valve in the pumping mechanism. The valve ensures that at any point in time, the proton pathway across the membrane is effectively discontinuous, thereby preventing thermodynamically favorable proton back-leakage while maintaining an overall high efficiency of proton translocation. Suppression of proton leakage is particularly important in mitochondria under physiological conditions, where production of ATP takes place in the presence of a high electrochemical proton gradient.
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Prevention of leak in the proton pump of cytochrome c oxidase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:890-2. [PMID: 18423393 DOI: 10.1016/j.bbabio.2008.03.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Revised: 02/22/2008] [Accepted: 03/19/2008] [Indexed: 11/21/2022]
Abstract
The cytochrome c oxidases (CcO), which are responsible for most O(2) consumption in biology, are also redox-linked proton pumps that effectively convert the free energy of O(2) reduction to an electrochemical proton gradient across mitochondrial and bacterial membranes. Recently, time-resolved measurements have elucidated the sequence of events in proton translocation, and shed light on the underlying molecular mechanisms. One crucial property of the proton pump mechanism has received less attention, viz. how proton leaks are avoided. Here, we will analyse this topic and demonstrate how the key proton-carrying residue Glu-242 (numbering according to the sequence of subunit I of bovine heart CcO) functions as a valve that has the effect of minimising back-leakage of the pumped proton.
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Tuukkanen A, Kaila VRI, Laakkonen L, Hummer G, Wikström M. Dynamics of the glutamic acid 242 side chain in cytochrome c oxidase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:1102-6. [PMID: 17706938 DOI: 10.1016/j.bbabio.2007.06.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Revised: 06/24/2007] [Accepted: 06/26/2007] [Indexed: 10/23/2022]
Abstract
In many cytochrome c oxidases glutamic acid 242 is required for proton transfer to the binuclear heme a(3)/Cu(B) site, and for proton pumping. When present, the side chain of Glu-242 is orientated "down" towards the proton-transferring D-pathway in all available crystal structures. A nonpolar cavity "above" Glu-242 is empty in these structures. Yet, proton transfer from Glu-242 to the binuclear site, and for proton-pumping, is well established, and the cavity has been proposed to at least transiently contain water molecules that would mediate proton transfer. Such proton transfer has been proposed to require isomerisation of the Glu-242 side chain into an "up" position pointing towards the cavity. Here, we have explored the molecular dynamics of the protonated Glu-242 side chain. We find that the "up" position is preferred energetically when the cavity contains four water molecules, but the "down" position is favoured with less water. We conclude that the cavity might be deficient in water in the crystal structures, possibly reflecting the "resting" state of the enzyme, and that the "up/down" equilibrium of Glu-242 may be coupled to the presence of active-site water molecules produced by O(2) reduction.
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Affiliation(s)
- Anne Tuukkanen
- Helsinki Bioenergetics Group, Structural Biology and Biophysics Programme, Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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22
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Abstract
A series of metalloprotein complexes embedded in a mitochondrial or bacterial membrane utilize electron transfer reactions to pump protons across the membrane and create an electrochemical potential (DeltamuH+). Current understanding of the principles of electron-driven proton transfer is discussed, mainly with respect to the wealth of knowledge available from studies of cytochrome c oxidase. Structural, experimental, and theoretical evidence supports the model of long-distance proton transfer via hydrogen-bonded water chains in proteins as well as the basic concept that proton uptake and release in a redox-driven pump are driven by charge changes at the membrane-embedded centers. Key elements in the pumping mechanism may include bound water, carboxylates, and the heme propionates, arginines, and associated water above the hemes. There is evidence for an important role of subunit III and proton backflow, but the number and nature of gating mechanisms remain elusive, as does the mechanism of physiological control of efficiency.
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Affiliation(s)
- Jonathan P. Hosler
- Department of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216;
| | - Shelagh Ferguson-Miller
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824; ,
| | - Denise A. Mills
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824; ,
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23
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Busenlehner LS, Salomonsson L, Brzezinski P, Armstrong RN. Mapping protein dynamics in catalytic intermediates of the redox-driven proton pump cytochrome c oxidase. Proc Natl Acad Sci U S A 2006; 103:15398-403. [PMID: 17023543 PMCID: PMC1622835 DOI: 10.1073/pnas.0601451103] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Redox-driven proton pumps such as cytochrome c oxidase (CcO) are fundamental elements of the energy transduction machinery in biological systems. CcO is an integral membrane protein that acts as the terminal electron acceptor in respiratory chains of aerobic organisms, catalyzing the four-electron reduction of O2 to H2O. This reduction also requires four protons taken from the cytosolic or negative side of the membrane, with an additional uptake of four protons that are pumped across the membrane. Therefore, the proton pump must embody a "gate," which provides alternating access of protons to one or the other side of the membrane but never both sides simultaneously. However, the exact mechanism of proton translocation through CcO remains unknown at the molecular level. Understanding pump function requires knowledge of the nature and location of these structural changes that is often difficult to access with crystallography or NMR spectroscopy. In this paper, we demonstrate, with amide hydrogen/deuterium exchange MS, that transitions between catalytic intermediates in CcO are orchestrated with opening and closing of specific proton pathways, providing an alternating access for protons to the two sides of the membrane. An analysis of these results in the framework of the 3D structure of CcO indicate the spatial location of a gate, which controls the unidirectional proton flux through the enzyme and points to a mechanism by which CcO energetically couples electron transfer to proton translocation.
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Affiliation(s)
| | - Lina Salomonsson
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Peter Brzezinski
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Richard N. Armstrong
- Departments of *Biochemistry and
- Chemistry, Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232-0146; and
- To whom correspondence should be addressed. E-mail:
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24
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Xu J, Voth GA. Free energy profiles for H+ conduction in the D-pathway of Cytochrome c Oxidase: a study of the wild type and N98D mutant enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:852-9. [PMID: 16815239 DOI: 10.1016/j.bbabio.2006.05.028] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 05/11/2006] [Accepted: 05/15/2006] [Indexed: 11/29/2022]
Abstract
The molecular mechanism for proton conduction in the D-pathway of Cytochrome c Oxidase (CcO) is investigated through the free energy profile, i.e., potential of mean force (PMF) calculations of both the native enzyme and the N98D mutant. The multistate empirical valence bond (MS-EVB) model was applied to simulate the interaction of an excess proton with the channel environment. In the study of the wild type enzyme, the PMF reveals the previously proposed proton trap inside the channel; it also shows a high free energy barrier against the passage of proton at the entry of the channel, where two conserved asparagines (ASN80/98) may be essential for the gating of proton uptake. We also present data from an investigation of the N98D mutant, which has been previously shown to completely eliminate proton pumping but significantly enhance the oxidase activity in Rhodobacter sphaeroides. These results suggest that mutating Asn98 to negatively charged aspartate will create an unfavorable energy barrier sufficiently high to prevent the overall proton uptake through the D-pathway, whereas with a protonated aspartic acid the proton conduction was found to be accelerated. Plausible explanations for the origin of the uncoupling of proton pumping from the oxidase activity will be discussed.
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Affiliation(s)
- Jiancong Xu
- Department of Chemistry, University of Utah, Salt Lake City, 84112-0850, USA
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25
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Wikström M, Ribacka C, Molin M, Laakkonen L, Verkhovsky M, Puustinen A. Gating of proton and water transfer in the respiratory enzyme cytochrome c oxidase. Proc Natl Acad Sci U S A 2005; 102:10478-81. [PMID: 16014708 PMCID: PMC1180778 DOI: 10.1073/pnas.0502873102] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The membrane-bound enzyme cytochrome c oxidase is responsible for cell respiration in aerobic organisms and conserves free energy from O2 reduction into an electrochemical proton gradient by coupling the redox reaction to proton-pumping across the membrane. O2 reduction produces water at the bimetallic heme a3/CuB active site next to a hydrophobic cavity deep within the membrane. Water molecules in this cavity have been suggested to play an important role in the proton-pumping mechanism. Here, we show by molecular dynamics simulations that the conserved arginine/heme a3 delta-propionate ion pair provides a gate, which exhibits reversible thermal opening that is governed by the redox state and the water molecules in the cavity. An important role of this gate in the proton-pumping mechanism is supported by site-directed mutagenesis experiments. Transport of the product water out of the enzyme must be rigidly controlled to prevent water-mediated proton leaks that could compromise the proton-pumping function. Exit of product water is observed through the same arginine/propionate gate, which provides an explanation for the observed extraordinary spatial specificity of water expulsion from the enzyme.
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Affiliation(s)
- Mårten Wikström
- Helsinki Bioenergetics Group, Institute of Biotechnology, Program for Structural Biology and Biophysics, University of Helsinki, PB 65 (Viikinkaari 1), 00014 Helsinki, Finland.
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26
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Xu J, Voth GA. Computer simulation of explicit proton translocation in cytochrome c oxidase: the D-pathway. Proc Natl Acad Sci U S A 2005; 102:6795-800. [PMID: 15857953 PMCID: PMC1100745 DOI: 10.1073/pnas.0408117102] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2004] [Indexed: 11/18/2022] Open
Abstract
Proton translocation in the D-pathway of cytochrome c oxidase has been studied by a combination of classical molecular dynamics and the multistate empirical valence bond methodology. This approach allows for explicit Grotthuss proton hopping between water molecules. According to mutagenesis experiments, the role of proton donor/acceptor along the D-pathway is carried by the highly conserved residue Glu-242. The present multistate empirical valence bond simulations indicate that the protonation/deprotonation state of Glu-242 is strongly coupled to the distance of proton propagation in the D-pathway. The proton was seen to travel the full length of the D-pathway when Glu-242 was deprotonated; however, it was trapped halfway along the path when Glu-242 was protonated. Further investigation in terms of both proton dynamical properties and free energy calculations for the pathway of proton transport provides evidence for a two-step proton transport mechanism in the D-pathway.
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Affiliation(s)
- Jiancong Xu
- Department of Chemistry and Center for Biophysical Modeling and Simulation, 315 South 1400 East Room 2020, University of Utah, Salt Lake City, UT 84112-0850, USA
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27
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Cukier RI. A molecular dynamics study of water chain formation in the proton-conducting K channel of cytochrome c oxidase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1706:134-46. [PMID: 15620374 DOI: 10.1016/j.bbabio.2004.10.004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2004] [Revised: 10/01/2004] [Accepted: 10/06/2004] [Indexed: 11/16/2022]
Abstract
The formation of water chains in cytochrome c oxidase (CcO) is studied by molecular dynamics (MD). Focus is on water chains in the K channel that can supply a proton to the binuclear center (the heme a3 Fe/CuB region), the site of O2 reduction. By assessing the presence of chains of any length on a short time scale (0.1 ps), a view of the kinds of chains and their persistence is obtained. Chains from the entry of the channel on the inner membrane to Thr359 (Rhodobacter sphaeroides numbering) are often present but are blocked at that point until a rotation of the Thr359 side chain occurs, permitting formation of chains from Thr359 towards the binuclear center. No continuous hydrogen-bonded water chains are found connecting Thr359 and the binuclear center. Instead, waters hydrogen bond from Thr359 to the hydroxyl of the heme a3 farnesyl and then continue to the binuclear center via Tyr288, which has been identified as a source of a proton for O2 reduction. Three hydrogen-bonded waters are found to be present in the binuclear center after a sufficiently long simulation time. One is ligated to the CuB and could be associated with a water (or hydroxyl) identified in the crystal structure as the fourth ligand of CuB. The water hydrogen-bonded to the hydroxyl of Tyr288 is extremely persistent and well positioned to participate in O2 reduction. The third water is located where O2 is often suggested to reside in mechanistic studies of O2 reduction.
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Affiliation(s)
- R I Cukier
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1322, USA.
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28
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Cukier R. A temperature-dependent Hartree approach for excess proton transport in hydrogen-bonded chains. Chem Phys 2004. [DOI: 10.1016/j.chemphys.2004.06.060] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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29
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Gutman M. Intra-protein proton transfer; presentation of the most massive flux in the biosphere at quantum chemistry resolution. Structure 2004; 12:1123-5. [PMID: 15242586 DOI: 10.1016/j.str.2004.06.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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