20 results on '"Bersch B"'
Search Results
2. Solution structure of the C-terminal domain of the vaccinia virus DNA polymerase processivity factor component A20.
- Author
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Bersch, B., primary, Iseni, F., additional, Burmeister, W., additional, and Tarbouriech, N., additional
- Published
- 2021
- Full Text
- View/download PDF
3. Bottom-up synthesis of vertically oriented two-dimensional materials
- Author
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Vilá, R A, primary, Momeni, K, additional, Wang, Q, additional, Bersch, B M, additional, Lu, N, additional, Kim, M J, additional, Chen, L Q, additional, and Robinson, J A, additional
- Published
- 2016
- Full Text
- View/download PDF
4. NMR structure of a 180 residue construct encompassing the N-terminal metal-binding site and the membrane proximal domain of SilB from Cupriavidus metallidurans CH34
- Author
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Bersch, B., primary, Urbina Fernandez, P., additional, and Vandenbussche, G., additional
- Published
- 2016
- Full Text
- View/download PDF
5. [Poxvirus-encoded DNA replication proteins: potential targets for antivirals].
- Author
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Tarbouriech N, Burmeister WP, Bersch B, and Iseni F
- Subjects
- Humans, DNA, DNA Replication, Antiviral Agents pharmacology, Antiviral Agents therapeutic use, Poxviridae genetics, Variola virus genetics, Mpox (monkeypox)
- Abstract
In the spring of 2022, an epidemic due to human monkeypox virus (MPXV) of unprecedented magnitude spread across all continents. Although this event was surprising in its suddenness, the resurgence of a virus from the Poxviridae family is not surprising in a world population that has been largely naïve to these viruses since the eradication of the smallpox virus in 1980 and the concomitant cessation of vaccination. Since then, a vaccine and two antiviral compounds have been developed to combat a possible return of smallpox. However, the use of these treatments during the 2022 MPXV epidemic showed certain limitations, indicating the importance of continuing to develop the therapeutic arsenal against these viruses. For several decades, efforts to understand the molecular mechanisms involved in the synthesis of the DNA genome of these viruses have been ongoing. Although many questions remain unanswered up to now, the three-dimensional structures of essential proteins, and in particular of the DNA polymerase holoenzyme in complex with DNA, make it possible to consider the development of a model for poxvirus DNA replication. In addition, these structures are valuable tools for the development of new antivirals targeting viral genome synthesis. This review will first present the molecules approved for the treatment of poxvirus infections, followed by a review of our knowledge of the replication machinery of these viruses. Finally, we will describe how these proteins could be the target of new antiviral compounds.
- Published
- 2024
- Full Text
- View/download PDF
6. Assessment of prediction methods for protein structures determined by NMR in CASP14: Impact of AlphaFold2.
- Author
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Huang YJ, Zhang N, Bersch B, Fidelis K, Inouye M, Ishida Y, Kryshtafovych A, Kobayashi N, Kuroda Y, Liu G, LiWang A, Swapna GVT, Wu N, Yamazaki T, and Montelione GT
- Subjects
- Computational Biology, Machine Learning, Protein Folding, Sequence Analysis, Protein, Magnetic Resonance Spectroscopy methods, Membrane Proteins chemistry, Membrane Proteins metabolism, Models, Molecular, Protein Conformation, Software
- Abstract
NMR studies can provide unique information about protein conformations in solution. In CASP14, three reference structures provided by solution NMR methods were available (T1027, T1029, and T1055), as well as a fourth data set of NMR-derived contacts for an integral membrane protein (T1088). For the three targets with NMR-based structures, the best prediction results ranged from very good (GDT_TS = 0.90, for T1055) to poor (GDT_TS = 0.47, for T1029). We explored the basis of these results by comparing all CASP14 prediction models against experimental NMR data. For T1027, NMR data reveal extensive internal dynamics, presenting a unique challenge for protein structure prediction methods. The analysis of T1029 motivated exploration of a novel method of "inverse structure determination," in which an AlphaFold2 model was used to guide NMR data analysis. NMR data provided to CASP predictor groups for target T1088, a 238-residue integral membrane porin, was also used to assess several NMR-assisted prediction methods. Most groups involved in this exercise generated similar beta-barrel models, with good agreement with the experimental data. However, as was also observed in CASP13, some pure prediction groups that did not use any NMR data generated models for T1088 that better fit the NMR data than the models generated using these experimental data. These results demonstrate the remarkable power of modern methods to predict structures of proteins with accuracies rivaling solution NMR structures, and that it is now possible to reliably use prediction models to guide and complement experimental NMR data analysis., (© 2021 The Authors. Proteins: Structure, Function, and Bioinformatics published by Wiley Periodicals LLC.)
- Published
- 2021
- Full Text
- View/download PDF
7. Scalable Characterization of 2D Gallium-Intercalated Epitaxial Graphene.
- Author
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El-Sherif H, Briggs N, Bersch B, Pan M, Hamidinejad M, Rajabpour S, Filleter T, Kim KW, Robinson J, and Bassim ND
- Abstract
Scalable synthesis of two-dimensional gallium (2D-Ga) covered by graphene layers was recently realized through confinement heteroepitaxy using silicon carbide substrates. However, the thickness, uniformity, and area coverage of the 2D-Ga heterostructures have not previously been studied with high-spatial resolution techniques. In this work, we resolve and measure the 2D-Ga heterostructure thicknesses using scanning electron microscopy (SEM). Utilizing multiple correlative methods, we find that SEM image contrast is directly related to the presence of uniform bilayer Ga at the interface and a variation of the number of graphene layers. We also investigate the origin of SEM contrast using both experimental measurements and theoretical calculations of the surface potentials. We find that a carbon buffer layer is detached due to the gallium intercalation, which increases the surface potential as an indication of the 2D-Ga presence. We then scale up the heterostructure characterization over a few-square millimeter area by segmenting SEM images, each acquired with nanometer-scale in-plane resolution. This work leverages the spectroscopic imaging capabilities of SEM that allows high-spatial resolution imaging for tracking intercalants, identifying relative surface potentials, determining the number of 2D layers, and further characterizing scalability and uniformity of low-dimensional materials.
- Published
- 2021
- Full Text
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8. How do Chaperones Bind (Partly) Unfolded Client Proteins?
- Author
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Sučec I, Bersch B, and Schanda P
- Abstract
Molecular chaperones are central to cellular protein homeostasis. Dynamic disorder is a key feature of the complexes of molecular chaperones and their client proteins, and it facilitates the client release towards a folded state or the handover to downstream components. The dynamic nature also implies that a given chaperone can interact with many different client proteins, based on physico-chemical sequence properties rather than on structural complementarity of their (folded) 3D structure. Yet, the balance between this promiscuity and some degree of client specificity is poorly understood. Here, we review recent atomic-level descriptions of chaperones with client proteins, including chaperones in complex with intrinsically disordered proteins, with membrane-protein precursors, or partially folded client proteins. We focus hereby on chaperone-client interactions that are independent of ATP. The picture emerging from these studies highlights the importance of dynamics in these complexes, whereby several interaction types, not only hydrophobic ones, contribute to the complex formation. We discuss these features of chaperone-client complexes and possible factors that may contribute to this balance of promiscuity and specificity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Sučec, Bersch and Schanda.)
- Published
- 2021
- Full Text
- View/download PDF
9. Solution Structure of the C-terminal Domain of A20, the Missing Brick for the Characterization of the Interface between Vaccinia Virus DNA Polymerase and its Processivity Factor.
- Author
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Bersch B, Tarbouriech N, Burmeister WP, and Iseni F
- Subjects
- Amino Acid Sequence, Catalytic Domain genetics, Crystallography, X-Ray, DNA, Viral chemistry, DNA, Viral genetics, DNA, Viral metabolism, DNA-Directed DNA Polymerase genetics, DNA-Directed DNA Polymerase metabolism, Holoenzymes chemistry, Holoenzymes genetics, Holoenzymes metabolism, Models, Molecular, Peptides chemistry, Peptides genetics, Peptides metabolism, Protein Binding, Sequence Homology, Amino Acid, Solutions chemistry, Vaccinia virus genetics, Viral Proteins genetics, Viral Proteins metabolism, Virus Replication genetics, DNA-Directed DNA Polymerase chemistry, Protein Domains, Vaccinia virus enzymology, Viral Proteins chemistry
- Abstract
Poxviruses are enveloped viruses with a linear, double-stranded DNA genome. Viral DNA synthesis is achieved by a functional DNA polymerase holoenzyme composed of three essential proteins. For vaccinia virus (VACV) these are E9, the catalytic subunit, a family B DNA polymerase, and the heterodimeric processivity factor formed by D4 and A20. The A20 protein links D4 to the catalytic subunit. High-resolution structures have been obtained for the VACV D4 protein in complex with an N-terminal fragment of A20 as well as for E9. In addition, biochemical studies provided evidence that a poxvirus-specific insertion (insert 3) in E9 interacts with the C-terminal residues of A20. Here, we provide solution structures of two different VACV A20 C-terminal constructs containing residues 304-426, fused at their C-terminus to either a BAP (Biotin Acceptor Peptide)-tag or a short peptide containing the helix of E9 insert 3. Together with results from titration studies, these structures shed light on the molecular interface between the catalytic subunit and the processivity factor component A20. The interface comprises hydrophobic residues conserved within the Chordopoxvirinae subfamily. Finally, we constructed a HADDOCK model of the VACV A20
304-426 -E9 complex, which is in excellent accordance with previous experimental data., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)- Published
- 2021
- Full Text
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10. Structural basis of client specificity in mitochondrial membrane-protein chaperones.
- Author
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Sučec I, Wang Y, Dakhlaoui O, Weinhäupl K, Jores T, Costa D, Hessel A, Brennich M, Rapaport D, Lindorff-Larsen K, Bersch B, and Schanda P
- Subjects
- Humans, Membrane Proteins metabolism, Mitochondrial Precursor Protein Import Complex Proteins, Scattering, Small Angle, X-Ray Diffraction, Mitochondrial Membranes metabolism, Molecular Chaperones chemistry
- Abstract
Chaperones are essential for assisting protein folding and for transferring poorly soluble proteins to their functional locations within cells. Hydrophobic interactions drive promiscuous chaperone-client binding, but our understanding of how additional interactions enable client specificity is sparse. Here, we decipher what determines binding of two chaperones (TIM8·13 and TIM9·10) to different integral membrane proteins, the all-transmembrane mitochondrial carrier Ggc1 and Tim23, which has an additional disordered hydrophilic domain. Combining NMR, SAXS, and molecular dynamics simulations, we determine the structures of Tim23/TIM8·13 and Tim23/TIM9·10 complexes. TIM8·13 uses transient salt bridges to interact with the hydrophilic part of its client, but its interactions to the transmembrane part are weaker than in TIM9·10. Consequently, TIM9·10 outcompetes TIM8·13 in binding hydrophobic clients, while TIM8·13 is tuned to few clients with both hydrophilic and hydrophobic parts. Our study exemplifies how chaperones fine-tune the balance of promiscuity versus specificity., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)
- Published
- 2020
- Full Text
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11. Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy.
- Author
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Briggs N, Bersch B, Wang Y, Jiang J, Koch RJ, Nayir N, Wang K, Kolmer M, Ko W, De La Fuente Duran A, Subramanian S, Dong C, Shallenberger J, Fu M, Zou Q, Chuang YW, Gai Z, Li AP, Bostwick A, Jozwiak C, Chang CZ, Rotenberg E, Zhu J, van Duin ACT, Crespi V, and Robinson JA
- Abstract
Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are 'half van der Waals' metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.
- Published
- 2020
- Full Text
- View/download PDF
12. The mitochondrial carrier pathway transports non-canonical substrates with an odd number of transmembrane segments.
- Author
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Rampelt H, Sucec I, Bersch B, Horten P, Perschil I, Martinou JC, van der Laan M, Wiedemann N, Schanda P, and Pfanner N
- Subjects
- Biological Transport, Mitochondria metabolism, Mitochondrial Membrane Transport Proteins metabolism, Mitochondrial Membranes metabolism, Molecular Chaperones metabolism, Saccharomyces cerevisiae metabolism, Saccharomyces cerevisiae Proteins metabolism
- Abstract
Background: The mitochondrial pyruvate carrier (MPC) plays a central role in energy metabolism by transporting pyruvate across the inner mitochondrial membrane. Its heterodimeric composition and homology to SWEET and semiSWEET transporters set the MPC apart from the canonical mitochondrial carrier family (named MCF or SLC25). The import of the canonical carriers is mediated by the carrier translocase of the inner membrane (TIM22) pathway and is dependent on their structure, which features an even number of transmembrane segments and both termini in the intermembrane space. The import pathway of MPC proteins has not been elucidated. The odd number of transmembrane segments and positioning of the N-terminus in the matrix argues against an import via the TIM22 carrier pathway but favors an import via the flexible presequence pathway., Results: Here, we systematically analyzed the import pathways of Mpc2 and Mpc3 and report that, contrary to an expected import via the flexible presequence pathway, yeast MPC proteins with an odd number of transmembrane segments and matrix-exposed N-terminus are imported by the carrier pathway, using the receptor Tom70, small TIM chaperones, and the TIM22 complex. The TIM9·10 complex chaperones MPC proteins through the mitochondrial intermembrane space using conserved hydrophobic motifs that are also required for the interaction with canonical carrier proteins., Conclusions: The carrier pathway can import paired and non-paired transmembrane helices and translocate N-termini to either side of the mitochondrial inner membrane, revealing an unexpected versatility of the mitochondrial import pathway for non-cleavable inner membrane proteins.
- Published
- 2020
- Full Text
- View/download PDF
13. Epitaxial graphene/silicon carbide intercalation: a minireview on graphene modulation and unique 2D materials.
- Author
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Briggs N, Gebeyehu ZM, Vera A, Zhao T, Wang K, De La Fuente Duran A, Bersch B, Bowen T, Knappenberger KL Jr, and Robinson JA
- Abstract
Intercalation of atomic species through epitaxial graphene on silicon carbide began only a few years following its initial report in 2004. The impact of intercalation on the electronic properties of the graphene is well known; however, the intercalant itself can also exhibit intriguing properties not found in nature. This realization has inspired new interest in epitaxial graphene/silicon carbide (EG/SiC) intercalation, where the scope of the technique extends beyond modulation of graphene properties to the creation of new 2D forms of 3D materials. The mission of this minireview is to provide a concise introduction to EG/SiC intercalation and to demonstrate a simplified approach to EG/SiC intercalation. We summarize the primary techniques used to achieve and characterize EG/SiC intercalation, and show that thermal evaporation-based methods can effectively substitute for more complex synthesis techniques, enabling large-scale intercalation of non-refractory metals and compounds including two-dimensional silver (2D-Ag) and gallium nitride (2D-GaN
x ).- Published
- 2019
- Full Text
- View/download PDF
14. Structural Basis of Membrane Protein Chaperoning through the Mitochondrial Intermembrane Space.
- Author
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Weinhäupl K, Lindau C, Hessel A, Wang Y, Schütze C, Jores T, Melchionda L, Schönfisch B, Kalbacher H, Bersch B, Rapaport D, Brennich M, Lindorff-Larsen K, Wiedemann N, and Schanda P
- Subjects
- Amino Acid Sequence, Binding Sites, Intracellular Membranes metabolism, Mitochondrial Membrane Transport Proteins chemistry, Mitochondrial Membrane Transport Proteins genetics, Molecular Dynamics Simulation, Mutagenesis, Site-Directed, Protein Binding, Protein Domains, Protein Precursors chemistry, Protein Precursors metabolism, Protein Structure, Secondary, Saccharomyces cerevisiae metabolism, Saccharomyces cerevisiae Proteins chemistry, Saccharomyces cerevisiae Proteins genetics, Sequence Alignment, Mitochondria metabolism, Mitochondrial Membrane Transport Proteins metabolism, Molecular Chaperones metabolism, Saccharomyces cerevisiae Proteins metabolism
- Abstract
The exchange of metabolites between the mitochondrial matrix and the cytosol depends on β-barrel channels in the outer membrane and α-helical carrier proteins in the inner membrane. The essential translocase of the inner membrane (TIM) chaperones escort these proteins through the intermembrane space, but the structural and mechanistic details remain elusive. We have used an integrated structural biology approach to reveal the functional principle of TIM chaperones. Multiple clamp-like binding sites hold the mitochondrial membrane proteins in a translocation-competent elongated form, thus mimicking characteristics of co-translational membrane insertion. The bound preprotein undergoes conformational dynamics within the chaperone binding clefts, pointing to a multitude of dynamic local binding events. Mutations in these binding sites cause cell death or growth defects associated with impairment of carrier and β-barrel protein biogenesis. Our work reveals how a single mitochondrial "transfer-chaperone" system is able to guide α-helical and β-barrel membrane proteins in a "nascent chain-like" conformation through a ribosome-free compartment., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)
- Published
- 2018
- Full Text
- View/download PDF
15. Dynamics and interactions of AAC3 in DPC are not functionally relevant.
- Author
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Kurauskas V, Hessel A, Dehez F, Chipot C, Bersch B, and Schanda P
- Subjects
- Adenosine Diphosphate, Adenosine Triphosphate, Magnetic Resonance Spectroscopy, Membrane Transport Proteins, Mitochondrial ADP, ATP Translocases
- Published
- 2018
- Full Text
- View/download PDF
16. How Detergent Impacts Membrane Proteins: Atomic-Level Views of Mitochondrial Carriers in Dodecylphosphocholine.
- Author
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Kurauskas V, Hessel A, Ma P, Lunetti P, Weinhäupl K, Imbert L, Brutscher B, King MS, Sounier R, Dolce V, Kunji ERS, Capobianco L, Chipot C, Dehez F, Bersch B, and Schanda P
- Subjects
- Mitochondrial ADP, ATP Translocases chemistry, Molecular Dynamics Simulation, Nuclear Magnetic Resonance, Biomolecular, Phosphorylcholine chemistry, Protein Conformation, Protein Stability, Saccharomyces cerevisiae chemistry, Saccharomyces cerevisiae Proteins chemistry, Detergents chemistry, Micelles, Mitochondrial Membrane Transport Proteins chemistry, Phosphorylcholine analogs & derivatives
- Abstract
Characterizing the structure of membrane proteins (MPs) generally requires extraction from their native environment, most commonly with detergents. Yet, the physicochemical properties of detergent micelles and lipid bilayers differ markedly and could alter the structural organization of MPs, albeit without general rules. Dodecylphosphocholine (DPC) is the most widely used detergent for MP structure determination by NMR, but the physiological relevance of several prominent structures has been questioned, though indirectly, by other biophysical techniques, e.g., functional/thermostability assay (TSA) and molecular dynamics (MD) simulations. Here, we resolve unambiguously this controversy by probing the functional relevance of three different mitochondrial carriers (MCs) in DPC at the atomic level, using an exhaustive set of solution-NMR experiments, complemented by functional/TSA and MD data. Our results provide atomic-level insight into the structure, substrate interaction and dynamics of the detergent-membrane protein complexes and demonstrates cogently that, while high-resolution NMR signals can be obtained for MCs in DPC, they systematically correspond to nonfunctional states.
- Published
- 2018
- Full Text
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17. Functional reconstitution of cell-free synthesized purified K v channels.
- Author
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Renauld S, Cortes S, Bersch B, Henry X, De Waard M, and Schaack B
- Subjects
- Elapid Venoms pharmacology, Escherichia coli genetics, Escherichia coli metabolism, Fluorescent Dyes chemistry, Gene Expression, Genetic Vectors chemistry, Genetic Vectors metabolism, Humans, Isoxazoles chemistry, Kv1.1 Potassium Channel genetics, Kv1.3 Potassium Channel genetics, Phosphatidylcholines chemistry, Phosphatidylcholines metabolism, Phosphatidylethanolamines chemistry, Phosphatidylethanolamines metabolism, Phosphatidylserines chemistry, Phosphatidylserines metabolism, Proteolipids chemistry, Proteolipids metabolism, Recombinant Proteins genetics, Recombinant Proteins metabolism, Subcellular Fractions metabolism, Valinomycin pharmacology, Kv1.1 Potassium Channel metabolism, Kv1.3 Potassium Channel metabolism, Membrane Potentials drug effects, Proteolipids drug effects
- Abstract
The study of ion channel activity and the screening of possible inhibitor molecules require reliable methods for production of active channel proteins, their insertion into artificial membranes and for the measurement of their activity. Here we report on cell-free expression of soluble and active K
v 1.1 and Kv 1.3 channels and their efficient insertion into liposomes. Two complementary methods for the determination of the electrical activity of the proteoliposome-embedded channels were compared using Kv 1.1 as a model system: (1) single channel recordings in droplet interface bilayers (DIB) and (2) measurement of the membrane voltage potential generated by a potassium ion diffusion potential using the voltage-sensitive fluorescent dye oxonol VI. Single channel recordings in DIBs proved unreliable because of the non-reproducible fusion of proteoliposomes with an artificial membrane. Therefore, the use of the optical indicator oxonol VI was adapted for 96 well microtiter plates using the ionophore valinomycin as a positive control. The activity of Kv 1.1 and Kv 1.3 channels was then monitored in the absence and presence of different venom toxins, demonstrating that fluorescent dyes can be used very efficiently when screening small molecules for their channel blocking activity., (Copyright © 2017 Elsevier B.V. All rights reserved.)- Published
- 2017
- Full Text
- View/download PDF
18. Proton-Detected Solid-State NMR Spectroscopy of a Zinc Diffusion Facilitator Protein in Native Nanodiscs.
- Author
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Bersch B, Dörr JM, Hessel A, Killian JA, and Schanda P
- Subjects
- Diffusion, Nanostructures chemistry, Proteolipids chemistry, Protons, Zinc chemistry, Bacterial Proteins chemistry, Cupriavidus chemistry, Maleates chemistry, Membrane Transport Proteins chemistry, Polystyrenes chemistry, Proton Magnetic Resonance Spectroscopy methods
- Abstract
The structure, dynamics, and function of membrane proteins are intimately linked to the properties of the membrane environment in which the proteins are embedded. For structural and biophysical characterization, membrane proteins generally need to be extracted from the membrane and reconstituted in a suitable membrane-mimicking environment. Ensuring functional and structural integrity in these environments is often a major concern. The styrene/maleic acid co-polymer has recently been shown to be able to extract lipid/membrane protein patches directly from native membranes to form nanosize discoidal proteolipid particles, also referred to as native nanodiscs. In this work, we show that high-resolution solid-state NMR spectra can be obtained from an integral membrane protein in native nanodiscs, as exemplified by the 2×34 kDa bacterial cation diffusion facilitator CzcD., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)
- Published
- 2017
- Full Text
- View/download PDF
19. Structural and Functional Investigation of the Ag(+)/Cu(+) Binding Domains of the Periplasmic Adaptor Protein SilB from Cupriavidus metallidurans CH34.
- Author
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Urbina P, Bersch B, De Angelis F, Derfoufi KM, Prévost M, Goormaghtigh E, and Vandenbussche G
- Subjects
- Carrier Proteins metabolism, Cupriavidus metabolism, Ion Transport, Nuclear Magnetic Resonance, Biomolecular, Periplasm metabolism, Periplasmic Proteins metabolism, Protein Domains, Silver metabolism, Spectrometry, Fluorescence, Carrier Proteins chemistry, Cupriavidus chemistry, Periplasm chemistry, Periplasmic Proteins chemistry, Silver chemistry
- Abstract
Silver ion resistance in bacteria mainly relies on efflux systems, and notably on tripartite efflux complexes involving a transporter from the resistance-nodulation-cell division (RND) superfamily, such as the SilCBA system from Cupriavidus metallidurans CH34. The periplasmic adaptor protein SilB hosts two specific metal coordination sites, located in the N-terminal and C-terminal domains, respectively, that are believed to play a different role in the efflux mechanism and the trafficking of metal ions from the periplasm to the RND transporter. On the basis of the known domain structure of periplasmic adaptor proteins, we designed different protein constructs derived from SilB domains with either one or two metal binding sites per protein chain. ITC data acquired on proteins with single metal sites suggest a slightly higher affinity of Ag(+) for the N-terminal metal site, compared to that for the C-terminal one. Remarkably, via the study of a protein construct featuring both metal sites, nuclear magnetic resonance (NMR) and fluorescence spectroscopies concordantly show that the C-terminal site is saturated prior to the N-terminal one. The C-terminal binding site is supposed to transfer the metal ions to the RND protein, while the transport driven by this latter is activated upon binding of the metal ion to the N-terminal site. Our results suggest that the filling of the C-terminal metal site is a key prerequisite for preventing futile activation of the transport system. Exhaustive NMR studies reveal for the first time the structure and dynamics of the functionally important N-terminal domain connected to the membrane proximal domain as well as of its Ag(+) binding site.
- Published
- 2016
- Full Text
- View/download PDF
20. Tungsten Ditelluride: a layered semimetal.
- Author
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Lee CH, Silva EC, Calderin L, Nguyen MA, Hollander MJ, Bersch B, Mallouk TE, and Robinson JA
- Abstract
Tungsten ditelluride (WTe2) is a transition metal dichalcogenide (TMD) with physical and electronic properties that make it attractive for a variety of electronic applications. Although WTe2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We experimentally and theoretically investigate the structure, dynamics and electronic properties of WTe2, and verify that WTe2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like transport. Our findings unambiguously confirm the metallic nature of WTe2, introduce new information about the Raman modes of Td-WTe2, and demonstrate that Td-WTe2 is readily oxidized via environmental exposure. Finally, these findings confirm that, in its thermodynamically favored Td form, the utilization of WTe2 in electronic device architectures such as field effect transistors may need to be reevaluated.
- Published
- 2015
- Full Text
- View/download PDF
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