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Teare P, Smith CF, Adams SJ, Anbu S, Ciani B, Jeuken LJC, Peacock AFA. pH dependent binding in de novo hetero bimetallic coiled coils. Dalton Trans 2018; 47:10784-10790. [PMID: 30022210 DOI: 10.1039/c8dt01568f] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Herein the first example of a bimetallic coiled coil featuring a lanthanide binding site is reported, opening opportunities to exploit the attractive NMR and photophysical properties of the lanthanides in multi metallo protein design. In our efforts to fully characterise the system we identified for the first time that lanthanide binding to such sites is pH dependent, with optimal binding at neutral pH, and that the double AsnAsp site is more versatile in this regard than the single Asp site. Our second site featured the structural HgCys3 site, the chemistry of which was essentially unaltered by the presence of the lanthanide site. In fact, both metal binding sites within the hetero bimetallic coiled coil displayed the same properties as their mononuclear single binding site controls, and operated independently of each other. Finally, pH can be used as an external trigger to control the binding of Hg(ii) and Tb(iii) to the two distinct sites within this coiled coil, and offers the opportunity to "activate" metal binding sites within complex multi metallo and multi-functional designs.
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Bawazer LA, Ihli J, Levenstein MA, Jeuken LJC, Meldrum FC, McMillan DGG. Enzymatically-controlled biomimetic synthesis of titania/protein hybrid thin films. J Mater Chem B 2018; 6:3979-3988. [PMID: 32254326 DOI: 10.1039/c8tb00381e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Although it is widely recognised that enzymes play a significant role in sculpting complex silica skeletons in marine sponges, the potential for exploiting enzymes in materials synthesis has not yet been fully harnessed. In this work we show that the digestive enzyme papain can self-assemble into monolayers on oxide surfaces, where they then drive the formation of crystalline titanium dioxide nanoparticles. This dual functionality of thin film formation and mineralization promotion has the potential to enable the construction of hierarchical inorganic/organic structures in the form of continuous amorphous titania/protein films which can be refined to 93% anatase post annealing. Additional control over the film thickness is afforded by layer-by-layer processing using a simple dip-coating approach. Papain's TiO2-mineralizing activity displays complex kinetics that deviates from the native Michaelis-Menten kinetic activity, yet deactivation studies demonstrate that this activity relies upon residues that are essential for catalytic site function. These parameters provide unique insight into enzymatic biomineralization, allowing a flexible route to achieving bioengineered titania heterostructures, and potentially providing a green-chemistry solution to photovoltaic cell development.
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Lee CY, Reuillard B, Sokol KP, Laftsoglou T, Lockwood CWJ, Rowe SF, Hwang ET, Fontecilla-Camps JC, Jeuken LJC, Butt JN, Reisner E. A decahaem cytochrome as an electron conduit in protein-enzyme redox processes. Chem Commun (Camb) 2018; 52:7390-3. [PMID: 27193068 DOI: 10.1039/c6cc02721k] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The decahaem cytochrome MtrC from Shewanella oneidensis MR-1 was employed as a protein electron conduit between a porous indium tin oxide electrode and redox enzymes. Using a hydrogenase and a fumarate reductase, MtrC was shown as a suitable and efficient diode to shuttle electrons to and from the electrode with the MtrC redox activity regulating the direction of the enzymatic reactions.
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Rowe SF, Le Gall G, Ainsworth EV, Davies JA, Lockwood CWJ, Shi L, Elliston A, Roberts IN, Waldron KW, Richardson DJ, Clarke TA, Jeuken LJC, Reisner E, Butt JN. Light-Driven H2 Evolution and C═C or C═O Bond Hydrogenation by Shewanella oneidensis: A Versatile Strategy for Photocatalysis by Nonphotosynthetic Microorganisms. ACS Catal 2017. [DOI: 10.1021/acscatal.7b02736] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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30
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Hwang ET, Orchard KL, Hojo D, Beton J, Lockwood CWJ, Adschiri T, Butt JN, Reisner E, Jeuken LJC. Exploring Step-by-Step Assembly of Nanoparticle:Cytochrome Biohybrid Photoanodes. ChemElectroChem 2017; 4:1959-1968. [PMID: 28920010 PMCID: PMC5573906 DOI: 10.1002/celc.201700030] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Indexed: 11/07/2022]
Abstract
Coupling light-harvesting semiconducting nanoparticles (NPs) with redox enzymes has been shown to create artificial photosynthetic systems that hold promise for the synthesis of solar fuels. High quantum yields require efficient electron transfer from the nanoparticle to the redox protein, a property that can be difficult to control. Here, we have compared binding and electron transfer between dye-sensitized TiO2 nanocrystals or CdS quantum dots and two decaheme cytochromes on photoanodes. The effect of NP surface chemistry was assessed by preparing NPs capped with amine or carboxylic acid functionalities. For the TiO2 nanocrystals, binding to the cytochromes was optimal when capped with a carboxylic acid ligand, whereas for the CdS QDs, better adhesion was observed for amine capped ligand shells. When using TiO2 nanocrystals, dye-sensitized with a phosphonated bipyridine Ru(II) dye, photocurrents are observed that are dependent on the redox state of the decaheme, confirming that electrons are transferred from the TiO2 nanocrystals to the surface via the decaheme conduit. In contrast, when CdS NPs are used, photocurrents are not dependent on the redox state of the decaheme, consistent with a model in which electron transfer from CdS to the photoanode bypasses the decaheme protein. These results illustrate that although the organic shell of NPs nanoparticles crucially affects coupling with proteinaceous material, the coupling can be difficult to predict or engineer.
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31
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Li M, Khan S, Rong H, Tuma R, Hatzakis NS, Jeuken LJC. Effects of membrane curvature and pH on proton pumping activity of single cytochrome bo 3 enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017. [PMID: 28634030 DOI: 10.1016/j.bbabio.2017.06.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The molecular mechanism of proton pumping by heme-copper oxidases (HCO) has intrigued the scientific community since it was first proposed. We have recently reported a novel technology that enables the continuous characterisation of proton transport activity of a HCO and ubiquinol oxidase from Escherichia coli, cytochrome bo3, for hundreds of seconds on the single enzyme level (Li et al. J Am Chem Soc 137 (2015) 16055-16063). Here, we have extended these studies by additional experiments and analyses of the proton transfer rate as a function of proteoliposome size and pH at the N- and P-side of single HCOs. Proton transport activity of cytochrome bo3 was found to decrease with increased curvature of the membrane. Furthermore, proton uptake at the N-side (proton entrance) was insensitive to pH between pH6.4-8.4, while proton release at the P-side had an optimum pH of ~7.4, suggesting that the pH optimum is related to proton release from the proton exit site. Our previous single-enzyme experiments identified rare, long-lived conformation states of cytochrome bo3 where protons leak back under turn-over conditions. Here, we analyzed and found that ~23% of cytochrome bo3 proteoliposomes show ΔpH half-lives below 50s after stopping turnover, while only ~5% of the proteoliposomes containing a non-pumping mutant, E286C cytochrome bo3 exhibit such fast decays. These single-enzyme results confirm our model in which HCO exhibit heterogeneous pumping rates and can adopt rare leak states in which protons are able to rapidly flow back.
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32
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Laftsoglou T, Jeuken LJC. Supramolecular electrode assemblies for bioelectrochemistry. Chem Commun (Camb) 2017; 53:3801-3809. [PMID: 28317998 PMCID: PMC5436043 DOI: 10.1039/c7cc01154g] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 03/14/2017] [Indexed: 12/03/2022]
Abstract
For more than three decades, the field of bioelectrochemistry has provided novel insights into the catalytic mechanisms of enzymes, the principles that govern biological electron transfer, and has elucidated the basic principles for bioelectrocatalytic systems. Progress in biochemistry, bionanotechnology, and our ever increasing ability to control the chemistry and structure of electrode surfaces has enabled the study of ever more complex systems with bioelectrochemistry. This feature article highlights developments over the last decade, where supramolecular approaches have been employed to develop electrode assemblies that increase enzyme loading on the electrode or create more biocompatible environments for membrane enzymes. Two approaches are particularly highlighted: the use of layer-by-layer assembly, and the modification of electrodes with planar lipid membranes.
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Reuillard B, Ly KH, Hildebrandt P, Jeuken LJC, Butt JN, Reisner E. High Performance Reduction of H 2O 2 with an Electron Transport Decaheme Cytochrome on a Porous ITO Electrode. J Am Chem Soc 2017; 139:3324-3327. [PMID: 28221032 PMCID: PMC5411108 DOI: 10.1021/jacs.6b12437] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Indexed: 11/28/2022]
Abstract
The decaheme cytochrome MtrC from Shewanella oneidensis MR-1 immobilized on an ITO electrode displays unprecedented H2O2 reduction activity. Although MtrC showed lower peroxidase activity in solution compared to horseradish peroxidase, the ten heme cofactors enable excellent electronic communication and a superior activity on the electrode surface. A hierarchical ITO electrode enabled optimal immobilization of MtrC and a high current density of 1 mA cm-2 at 0.4 V vs SHE could be obtained at pH 6.5 (Eonset = 0.72 V). UV-visible and Resonance Raman spectroelectrochemical studies suggest the formation of a high valent iron-oxo species as the catalytic intermediate. Our findings demonstrate the potential of multiheme cytochromes to catalyze technologically relevant reactions and establish MtrC as a new benchmark in biotechnological H2O2 reduction with scope for applications in fuel cells and biosensors.
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Beales PA, Khan S, Muench SP, Jeuken LJC. Durable vesicles for reconstitution of membrane proteins in biotechnology. Biochem Soc Trans 2017; 45:15-26. [PMID: 28202656 PMCID: PMC5310719 DOI: 10.1042/bst20160019] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 10/14/2016] [Accepted: 10/19/2016] [Indexed: 12/31/2022]
Abstract
The application of membrane proteins in biotechnology requires robust, durable reconstitution systems that enhance their stability and support their functionality in a range of working environments. Vesicular architectures are highly desirable to provide the compartmentalisation to utilise the functional transmembrane transport and signalling properties of membrane proteins. Proteoliposomes provide a native-like membrane environment to support membrane protein function, but can lack the required chemical and physical stability. Amphiphilic block copolymers can also self-assemble into polymersomes: tough vesicles with improved stability compared with liposomes. This review discusses the reconstitution of membrane proteins into polymersomes and the more recent development of hybrid vesicles, which blend the robust nature of block copolymers with the biofunctionality of lipids. These novel synthetic vesicles hold great promise for enabling membrane proteins within biotechnologies by supporting their enhanced in vitro performance and could also contribute to fundamental biochemical and biophysical research by improving the stability of membrane proteins that are challenging to work with.
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Ainsworth EV, Lockwood CWJ, White GF, Hwang ET, Sakai T, Gross MA, Richardson DJ, Clarke TA, Jeuken LJC, Reisner E, Butt JN. Cover Picture: Photoreduction of Shewanella oneidensis
Extracellular Cytochromes by Organic Chromophores and Dye-Sensitized TiO2
(ChemBioChem 24/2016). Chembiochem 2016. [DOI: 10.1002/cbic.201600602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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36
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Ainsworth EV, Lockwood CWJ, White GF, Hwang ET, Sakai T, Gross MA, Richardson DJ, Clarke TA, Jeuken LJC, Reisner E, Butt JN. Photoreduction of Shewanella oneidensis Extracellular Cytochromes by Organic Chromophores and Dye-Sensitized TiO 2. Chembiochem 2016; 17:2324-2333. [PMID: 27685371 PMCID: PMC5215560 DOI: 10.1002/cbic.201600339] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Indexed: 12/28/2022]
Abstract
The transfer of photoenergized electrons from extracellular photosensitizers across a bacterial cell envelope to drive intracellular chemical transformations represents an attractive way to harness nature's catalytic machinery for solar-assisted chemical synthesis. In Shewanella oneidensis MR-1 (MR-1), trans-outer-membrane electron transfer is performed by the extracellular cytochromes MtrC and OmcA acting together with the outer-membrane-spanning porin⋅cytochrome complex (MtrAB). Here we demonstrate photoreduction of solutions of MtrC, OmcA, and the MtrCAB complex by soluble photosensitizers: namely, eosin Y, fluorescein, proflavine, flavin, and adenine dinucleotide, as well as by riboflavin and flavin mononucleotide, two compounds secreted by MR-1. We show photoreduction of MtrC and OmcA adsorbed on RuII -dye-sensitized TiO2 nanoparticles and that these protein-coated particles perform photocatalytic reduction of solutions of MtrC, OmcA, and MtrCAB. These findings provide a framework for informed development of strategies for using the outer-membrane-associated cytochromes of MR-1 for solar-driven microbial synthesis in natural and engineered bacteria.
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37
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Khan S, Li M, Muench SP, Jeuken LJC, Beales PA. Durable proteo-hybrid vesicles for the extended functional lifetime of membrane proteins in bionanotechnology. Chem Commun (Camb) 2016; 52:11020-3. [PMID: 27540604 PMCID: PMC5048396 DOI: 10.1039/c6cc04207d] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Significant enhancement of membrane protein functional durability is demonstrated when reconstituted in hybrid lipid–block copolymer vesicles compared to conventional proteoliposomes.
The full capabilities of membrane proteins in bionanotechnology can only be realised through improvements in their reconstitution environments that combine biocompatibility to support function and durability for long term stability. We demonstrate that hybrid vesicles composed of natural phospholipids and synthetic diblock copolymers have the potential to achieve these criteria.
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Ye S, Benz F, Wheeler MC, Oram J, Baumberg JJ, Cespedes O, Christenson HK, Coletta PL, Jeuken LJC, Markham AF, Critchley K, Evans SD. One-step fabrication of hollow-channel gold nanoflowers with excellent catalytic performance and large single-particle SERS activity. NANOSCALE 2016; 8:14932-14942. [PMID: 27352044 DOI: 10.1039/c6nr04045d] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Hollow metallic nanostructures have shown potential in various applications including catalysis, drug delivery and phototherapy, owing to their large surface areas, reduced net density, and unique optical properties. In this study, novel hollow gold nanoflowers (HAuNFs) consisting of an open hollow channel in the center and multiple branches/tips on the outer surface are fabricated for the first time, via a facile one-step synthesis using an auto-degradable nanofiber as a bifunctional template. The one-dimensional (1D) nanofiber acts as both a threading template as well as a promoter of the anisotropic growth of the gold crystal, the combination of which leads to the formation of HAuNFs with a hollow channel and nanospikes. The synergy of favorable structural/surface features, including sharp edges, open cavity and high-index facets, provides our HAuNFs with excellent catalytic performance (activity and cycling stability) coupled with large single-particle SERS activity (including ∼30 times of activity in ethanol electro-oxidation and ∼40 times of single-particle SERS intensity, benchmarked against similar-sized solid gold nanospheres with smooth surfaces, as well as retaining 86.7% of the initial catalytic activity after 500 cycles in ethanol electro-oxidation). This innovative synthesis gives a nanostructure of the geometry distinct from the template and is extendable to fabricating other systems for example, hollow-channel silver nanoflowers (HAgNFs). It thus provides an insight into the design of hollow nanostructures via template methods, and offers a versatile synthetic strategy for diverse metal nanomaterials suited for a broad range of applications.
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Wiebalck S, Kozuch J, Forbrig E, Tzschucke CC, Jeuken LJC, Hildebrandt P. Monitoring the Transmembrane Proton Gradient Generated by Cytochrome bo3 in Tethered Bilayer Lipid Membranes Using SEIRA Spectroscopy. J Phys Chem B 2016; 120:2249-56. [DOI: 10.1021/acs.jpcb.6b01435] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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40
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Oram J, Jeuken LJC. A Re-evaluation of Electron-Transfer Mechanisms in Microbial Electrochemistry: Shewanella Releases Iron that Mediates Extracellular Electron Transfer. ChemElectroChem 2016; 3:829-835. [PMID: 27668145 PMCID: PMC5021177 DOI: 10.1002/celc.201500505] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Indexed: 12/11/2022]
Abstract
Exoelectrogenic bacteria can couple their metabolism to extracellular electron acceptors, including macroscopic electrodes, and this has applications in energy production, bioremediation and biosensing. Optimisation of these technologies relies on a detailed molecular understanding of extracellular electron‐transfer (EET) mechanisms, and Shewanella oneidensis MR‐1 (MR‐1) has become a model organism for such fundamental studies. Here, cyclic voltammetry was used to determine the relationship between the surface chemistry of electrodes (modified gold, ITO and carbon electrodes) and the EET mechanism. On ultra‐smooth gold electrodes modified with self‐assembled monolayers containing carboxylic‐acid‐terminated thiols, an EET pathway dominates with an oxidative catalytic onset at 0.1 V versus SHE. Addition of iron(II)chloride enhances the catalytic current, whereas the siderophore deferoxamine abolishes this signal, leading us to conclude that this pathway proceeds via an iron mediated electron transfer mechanism. The same EET pathway is observed at other electrodes, but the onset potential is dependent on the electrolyte composition and electrode surface chemistry. EET pathways with onset potentials above −0.1 V versus SHE have previously been ascribed to direct electron‐transfer (DET) mechanisms through the surface exposed decaheme cytochromes (MtrC/OmcA) of MR‐1. In light of the results reported here, we propose that the previously identified DET mechanism of MR‐1 needs to be re‐evaluated.
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Radu V, Frielingsdorf S, Lenz O, Jeuken LJC. Reactivation from the Ni–B state in [NiFe] hydrogenase of Ralstonia eutropha is controlled by reduction of the superoxidised proximal cluster. Chem Commun (Camb) 2016; 52:2632-5. [DOI: 10.1039/c5cc10382g] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The tolerance towards oxic conditions of O2-tolerant [NiFe] hydrogenases has been attributed to an unusual [4Fe–3S] cluster that lies proximal to the [NiFe] active site.
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Li M, Jørgensen SK, McMillan DGG, Krzemiński Ł, Daskalakis NN, Partanen RH, Tutkus M, Tuma R, Stamou D, Hatzakis NS, Jeuken LJC. Single Enzyme Experiments Reveal a Long-Lifetime Proton Leak State in a Heme-Copper Oxidase. J Am Chem Soc 2015; 137:16055-63. [PMID: 26618221 PMCID: PMC4697922 DOI: 10.1021/jacs.5b08798] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Heme-copper oxidases (HCOs) are key
enzymes in prokaryotes and
eukaryotes for energy production during aerobic respiration. They
catalyze the reduction of the terminal electron acceptor, oxygen,
and utilize the Gibbs free energy to transport protons across a membrane
to generate a proton (ΔpH) and electrochemical gradient termed
proton motive force (PMF), which provides the driving force for the
adenosine triphosphate (ATP) synthesis. Excessive PMF is known to
limit the turnover of HCOs, but the molecular mechanism of this regulatory
feedback remains relatively unexplored. Here we present a single-enzyme
study that reveals that cytochrome bo3 from Escherichia coli, an HCO closely homologous
to Complex IV in human mitochondria, can enter a rare, long-lifetime
leak state during which proton flow is reversed. The probability of
entering the leak state is increased at higher ΔpH. By rapidly
dissipating the PMF, we propose that this leak state may enable cytochrome bo3, and possibly other HCOs, to maintain a suitable
ΔpH under extreme redox conditions.
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43
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Heath GR, Li M, Polignano IL, Richens JL, Catucci G, O’Shea P, Sadeghi SJ, Gilardi G, Butt JN, Jeuken LJC. Layer-by-Layer Assembly of Supported Lipid Bilayer Poly-l-Lysine Multilayers. Biomacromolecules 2015; 17:324-35. [DOI: 10.1021/acs.biomac.5b01434] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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44
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Hwang ET, Sheikh K, Orchard KL, Hojo D, Radu V, Lee CY, Ainsworth E, Lockwood C, Gross MA, Adschiri T, Reisner E, Butt JN, Jeuken LJC. A Decaheme Cytochrome as a Molecular Electron Conduit in Dye-Sensitized Photoanodes. ADVANCED FUNCTIONAL MATERIALS 2015; 25:2308-2315. [PMID: 26180522 PMCID: PMC4493899 DOI: 10.1002/adfm.201404541] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Revised: 02/05/2015] [Indexed: 06/04/2023]
Abstract
In nature, charge recombination in light-harvesting reaction centers is minimized by efficient charge separation. Here, it is aimed to mimic this by coupling dye-sensitized TiO2 nanocrystals to a decaheme protein, MtrC from Shewanella oneidensis MR-1, where the 10 hemes of MtrC form a ≈7-nm-long molecular wire between the TiO2 and the underlying electrode. The system is assembled by forming a densely packed MtrC film on an ultra-flat gold electrode, followed by the adsorption of approximately 7 nm TiO2 nanocrystals that are modified with a phosphonated bipyridine Ru(II) dye (RuP). The step-by-step construction of the MtrC/TiO2 system is monitored with (photo)electrochemistry, quartz-crystal microbalance with dissipation (QCM-D), and atomic force microscopy (AFM). Photocurrents are dependent on the redox state of the MtrC, confirming that electrons are transferred from the TiO2 nanocrystals to the surface via the MtrC conduit. In other words, in these TiO2/MtrC hybrid photodiodes, MtrC traps the conduction-band electrons from TiO2 before transferring them to the electrode, creating a photobioelectrochemical system in which a redox protein is used to mimic the efficient charge separation found in biological photosystems.
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Radu V, Frielingsdorf S, Evans SD, Lenz O, Jeuken LJC. Enhanced oxygen-tolerance of the full heterotrimeric membrane-bound [NiFe]-hydrogenase of Ralstonia eutropha. J Am Chem Soc 2014; 136:8512-5. [PMID: 24866391 PMCID: PMC4073834 DOI: 10.1021/ja503138p] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Hydrogenases are oxygen-sensitive enzymes that catalyze the conversion between protons and hydrogen. Water-soluble subcomplexes of membrane-bound [NiFe]-hydrogenases (MBH) have been extensively studied for applications in hydrogen-oxygen fuel cells as they are relatively tolerant to oxygen, although even these catalysts are still inactivated in oxidative conditions. Here, the full heterotrimeric MBH of Ralstonia eutropha, including the membrane-integral cytochrome b subunit, was investigated electrochemically using electrodes modified with planar tethered bilayer lipid membranes (tBLM). Cyclic voltammetry and chronoamperometry experiments show that MBH, in equilibrium with the quinone pool in the tBLM, does not anaerobically inactivate under oxidative redox conditions. In aerobic environments, the MBH is reversibly inactivated by O2, but reactivation was found to be fast even under oxidative redox conditions. This enhanced resistance to inactivation is ascribed to the oligomeric state of MBH in the lipid membrane.
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Mu Q, David CA, Galceran J, Rey-Castro C, Krzemiński L, Wallace R, Bamiduro F, Milne SJ, Hondow NS, Brydson R, Vizcay-Barrena G, Routledge MN, Jeuken LJC, Brown AP. Systematic investigation of the physicochemical factors that contribute to the toxicity of ZnO nanoparticles. Chem Res Toxicol 2014; 27:558-67. [PMID: 24575710 DOI: 10.1021/tx4004243] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
ZnO nanoparticles (NPs) are prone to dissolution, and uncertainty remains whether biological/cellular responses to ZnO NPs are solely due to the release of Zn(2+) or whether the NPs themselves have additional toxic effects. We address this by establishing ZnO NP solubility in dispersion media (Dulbecco's modified Eagle's medium, DMEM) held under conditions identical to those employed for cell culture (37 °C, 5% CO2, and pH 7.68) and by systematic comparison of cell-NP interaction for three different ZnO NP preparations. For NPs at concentrations up to 5.5 μg ZnO/mL, dissolution is complete (with the majority of the soluble zinc complexed to dissolved ligands in the medium), taking ca. 1 h for uncoated and ca. 6 h for polymer coated ones. Above 5.5 μg/mL, the results are consistent with the formation of zinc carbonate, keeping the solubilized zinc fixed to 67 μM of which only 0.45 μM is as free Zn(2+), i.e., not complexed to dissolved ligands. At these relatively high concentrations, NPs with an aliphatic polyether-coating show slower dissolution (i.e., slower free Zn(2+) release) and reprecipitation kinetics compared to those of uncoated NPs, requiring more than 48 h to reach thermodynamic equilibrium. Cytotoxicity (MTT) and DNA damage (Comet) assay dose-response curves for three epithelial cell lines suggest that dissolution and reprecipitation dominate for uncoated ZnO NPs. Transmission electron microscopy combined with the monitoring of intracellular Zn(2+) concentrations and ZnO-NP interactions with model lipid membranes indicate that an aliphatic polyether coat on ZnO NPs increases cellular uptake, enhancing toxicity by enabling intracellular dissolution and release of Zn(2+). Similarly, we demonstrate that needle-like NP morphologies enhance toxicity by apparently frustrating cellular uptake. To limit toxicity, ZnO NPs with nonacicular morphologies and coatings that only weakly interact with cellular membranes are recommended.
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McMillan DGG, Marritt SJ, Kemp GL, Gordon-Brown P, Butt JN, Jeuken LJC. The Impact of Enzyme Orientation and Electrode Topology on the Catalytic Activity of Adsorbed Redox Enzymes. Electrochim Acta 2013; 110:79-85. [PMID: 24634538 DOI: 10.1016/j.electacta.2013.01.153] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200 nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes.
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McMillan DGG, Marritt SJ, Firer-Sherwood MA, Shi L, Richardson DJ, Evans SD, Elliott SJ, Butt JN, Jeuken LJC. Protein-protein interaction regulates the direction of catalysis and electron transfer in a redox enzyme complex. J Am Chem Soc 2013; 135:10550-6. [PMID: 23799249 PMCID: PMC3823026 DOI: 10.1021/ja405072z] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
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Protein–protein interactions
are well-known to regulate
enzyme activity in cell signaling and metabolism. Here, we show that
protein–protein interactions regulate the activity of a respiratory-chain
enzyme, CymA, by changing the direction or bias of catalysis. CymA,
a member of the widespread NapC/NirT superfamily, is a menaquinol-7
(MQ-7) dehydrogenase that donates electrons to several distinct terminal
reductases in the versatile respiratory network of Shewanella oneidensis. We report the incorporation
of CymA within solid-supported membranes that mimic the inner membrane
architecture of S. oneidensis. Quartz-crystal
microbalance with dissipation (QCM-D) resolved the formation of a
stable complex between CymA and one of its native redox partners,
flavocytochrome c3 (Fcc3) fumarate reductase.
Cyclic voltammetry revealed that CymA alone could only reduce MQ-7,
while the CymA-Fcc3 complex catalyzed the reaction required
to support anaerobic respiration, the oxidation of MQ-7. We propose
that MQ-7 oxidation in CymA is limited by electron transfer to the
hemes and that complex formation with Fcc3 facilitates
the electron-transfer rate along the heme redox chain. These results
reveal a yet unexplored mechanism by which bacteria can regulate multibranched
respiratory networks through protein–protein interactions.
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Booth M, Peel R, Partanen R, Hondow N, Vasilca V, Jeuken LJC, Critchley K. Amphipol-encapsulated CuInS2/ZnS quantum dots with excellent colloidal stability. RSC Adv 2013. [DOI: 10.1039/c3ra43846e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Mu Q, Hondow NS, Krzemiński L, Brown AP, Jeuken LJC, Routledge MN. Mechanism of cellular uptake of genotoxic silica nanoparticles. Part Fibre Toxicol 2012; 9:29. [PMID: 22823932 PMCID: PMC3479067 DOI: 10.1186/1743-8977-9-29] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Accepted: 07/12/2012] [Indexed: 12/30/2022] Open
Abstract
Mechanisms for cellular uptake of nanoparticles have important implications for nanoparticulate drug delivery and toxicity. We have explored the mechanism of uptake of amorphous silica nanoparticles of 14 nm diameter, which agglomerate in culture medium to hydrodynamic diameters around 500 nm. In HT29, HaCat and A549 cells, cytotoxicity was observed at nanoparticle concentrations ≥ 1 μg/ml, but DNA damage was evident at 0.1 μg/ml and above. Transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy confirmed entry of the silica particles into A549 cells exposed to 10 μg/ml of nanoparticles. The particles were observed in the cytoplasm but not within membrane bound vesicles or in the nucleus. TEM of cells exposed to nanoparticles at 4°C for 30 minutes showed particles enter cells when activity is low, suggesting a passive mode of entry. Plasma lipid membrane models identified physical interactions between the membrane and the silica NPs. Quartz crystal microbalance experiments on tethered bilayer lipid membrane systems show that the nanoparticles strongly bind to lipid membranes, forming an adherent monolayer on the membrane. Leakage assays on large unilamellar vesicles (400 nm diameter) indicate that binding of the silica NPs transiently disrupts the vesicles which rapidly self-seal. We suggest that an adhesive interaction between silica nanoparticles and lipid membranes could cause passive cellular uptake of the particles.
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