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Dufourc EJ. Bicelles and nanodiscs for biophysical chemistry. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1863:183478. [PMID: 32971065 DOI: 10.1016/j.bbamem.2020.183478] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 09/14/2020] [Accepted: 09/15/2020] [Indexed: 01/14/2023]
Abstract
Membrane nanoobjects are very important tools to study biomembrane properties. Two types are described herein: Bicelles and Nanodiscs. Bicelles are obtained by thorough water mixing of long chain and short chain lipids and may take the form of membranous discs of 10-50 nm. Temperature-composition-hydration diagrams have been established for Phosphatidylcholines and show limited domains of existence. Bicelles can be doped with charged lipids, surfactants or with cholesterol and offer a wide variety of membranous platforms for structural biology. Internal dynamics as measured by solid-state NMR is very similar to that of liposomes in their fluid phase. Because of the magnetic susceptibility anisotropy of the lipid chains, discs may be aligned along or perpendicular to the magnetic field. They may serve as weak orienting media to provide distance information in determining the 3D structure of soluble proteins. In different conditions they show strong orienting properties which may be used to study the 3D structure, topology and dynamics of membrane proteins. Lipid Bicelles with biphenyl chains or doped with lanthanides show long lasting remnant orientation after removing the magnetic field due to smectic-like properties. An alternative to pure lipid Bicelles is provided by nanodiscs where the half torus composed by short chain lipids is replaced by proteins. This renders the nano-objects less fragile as they can be used to stabilize membrane protein assemblies to be studied by electron microscopy. Internal dynamics is again similar to liposomes except that the phase transition is abolished, possibly due to lateral constrain imposed by the toroidal proteins limiting the disc size. Advantages and drawbacks of both nanoplatforms are discussed.
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Affiliation(s)
- Erick J Dufourc
- Institute of Chemistry and Biology of membranes and Nanoobjects, UMR5248, CNRS, University of Bordeaux, Bordeaux Polytechnic Institute, Allée Geoffroy Saint Hilaire, 33600 Pessac, France.
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Hasan M, Patel D, Ellis N, Brown SP, Lewandowski JR, Dixon AM. Modulation of Transmembrane Domain Interactions in Neu Receptor Tyrosine Kinase by Membrane Fluidity and Cholesterol. J Membr Biol 2019; 252:357-369. [DOI: 10.1007/s00232-019-00075-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 06/09/2019] [Indexed: 01/06/2023]
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3
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Aisenbrey C, Kemayo-Koumkoua P, Salnikov ES, Glattard E, Bechinger B. Investigations of the Structure, Topology, and Interactions of the Transmembrane Domain of the Lipid-Sorting Protein p24 Being Highly Selective for Sphingomyelin-C18. Biochemistry 2019; 58:2782-2795. [PMID: 31120242 DOI: 10.1021/acs.biochem.9b00375] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The p24 proteins play an important role in the secretory pathway where they selectively connect various cargo to other proteins, thereby being involved in the controlled assembly and disassembly of the coat protein complexes and lipid sorting. Recently, a highly selective lipid interaction motif has been identified within the p24 transmembrane domain (TMD) that recognizes the combination of the sphingomyelin headgroup and the exact length of the C18 fatty acyl chain (SM-C18). Here, we present investigations of the structure, dynamics, and sphingomyelin interactions of the p24 transmembrane region using circular dichroism, tryptophan fluorescence, and solid-state nuclear magnetic resonance (NMR) spectroscopies of the polypeptides and the surrounding lipids. Membrane insertion and/or conformation of the TMD is strongly dependent on the membrane lipid composition where the transmembrane helical insertion is strongest in the presence of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) and SM-C18. By analyzing solid-state NMR angular restraints from a large number of labeled sites, we have found a tilt angle of 19° for the transmembrane helical domain at a peptide-to-lipid ratio of 1 mol %. Only minor changes in the solid-state NMR spectra are observed due to the presence of SM-C18; the only visible alterations are associated with the SM-C18 recognition motif close to the carboxy-terminal part of the hydrophobic transmembrane region in the proximity of the SM headgroup. Finally, the deuterium order parameters of POPC- d31 were nearly unaffected by the presence of SM-C18 or the polypeptide alone but decreased noticeably when the sphingomyelin and the polypeptide were added in combination.
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Affiliation(s)
- Christopher Aisenbrey
- Université de Strasbourg/CNRS, UMR7177 , Institut de Chimie , 4, rue Blaise Pascal , 67070 Strasbourg , France
| | - Patricia Kemayo-Koumkoua
- Université de Strasbourg/CNRS, UMR7177 , Institut de Chimie , 4, rue Blaise Pascal , 67070 Strasbourg , France
| | - Evgeniy S Salnikov
- Université de Strasbourg/CNRS, UMR7177 , Institut de Chimie , 4, rue Blaise Pascal , 67070 Strasbourg , France
| | - Elise Glattard
- Université de Strasbourg/CNRS, UMR7177 , Institut de Chimie , 4, rue Blaise Pascal , 67070 Strasbourg , France
| | - Burkhard Bechinger
- Université de Strasbourg/CNRS, UMR7177 , Institut de Chimie , 4, rue Blaise Pascal , 67070 Strasbourg , France
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Botz A, Gasparik V, Devillers E, Hoffmann ARF, Caillon L, Chelain E, Lequin O, Brigaud T, Khemtemourian L. (R)-α-trifluoromethylalanine containing short peptide in the inhibition of amyloid peptide fibrillation. Biopolymers 2015; 104:601-10. [DOI: 10.1002/bip.22670] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 03/16/2015] [Accepted: 05/04/2015] [Indexed: 12/25/2022]
Affiliation(s)
- Alexandra Botz
- Sorbonne Universités, UPMC Univ Paris 06, Laboratoire des Biomolécules; 4 Place Jussieu F-75005 Paris France
- Ecole Normale Supérieure-PSL Research University, Département De Chimie; 24 rue Lhomond F-75005 Paris France
- CNRS, UMR 7203 Laboratoire Des Biomolécules; F-75005 Paris France
| | - Vincent Gasparik
- Laboratoire De Chimie Biologique, Université De Cergy-Pontoise; EA 4505, 5 Mail Gay-Lussac 95000 Cergy-Pontoise France
| | - Emmanuelle Devillers
- Laboratoire De Chimie Biologique, Université De Cergy-Pontoise; EA 4505, 5 Mail Gay-Lussac 95000 Cergy-Pontoise France
| | - Anais R. F. Hoffmann
- Sorbonne Universités, UPMC Univ Paris 06, Laboratoire des Biomolécules; 4 Place Jussieu F-75005 Paris France
- Ecole Normale Supérieure-PSL Research University, Département De Chimie; 24 rue Lhomond F-75005 Paris France
- CNRS, UMR 7203 Laboratoire Des Biomolécules; F-75005 Paris France
| | - Lucie Caillon
- Sorbonne Universités, UPMC Univ Paris 06, Laboratoire des Biomolécules; 4 Place Jussieu F-75005 Paris France
- Ecole Normale Supérieure-PSL Research University, Département De Chimie; 24 rue Lhomond F-75005 Paris France
- CNRS, UMR 7203 Laboratoire Des Biomolécules; F-75005 Paris France
| | - Evelyne Chelain
- Laboratoire De Chimie Biologique, Université De Cergy-Pontoise; EA 4505, 5 Mail Gay-Lussac 95000 Cergy-Pontoise France
| | - Olivier Lequin
- Sorbonne Universités, UPMC Univ Paris 06, Laboratoire des Biomolécules; 4 Place Jussieu F-75005 Paris France
- Ecole Normale Supérieure-PSL Research University, Département De Chimie; 24 rue Lhomond F-75005 Paris France
- CNRS, UMR 7203 Laboratoire Des Biomolécules; F-75005 Paris France
| | - Thierry Brigaud
- Laboratoire De Chimie Biologique, Université De Cergy-Pontoise; EA 4505, 5 Mail Gay-Lussac 95000 Cergy-Pontoise France
| | - Lucie Khemtemourian
- Sorbonne Universités, UPMC Univ Paris 06, Laboratoire des Biomolécules; 4 Place Jussieu F-75005 Paris France
- Ecole Normale Supérieure-PSL Research University, Département De Chimie; 24 rue Lhomond F-75005 Paris France
- CNRS, UMR 7203 Laboratoire Des Biomolécules; F-75005 Paris France
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The proline-rich antimicrobial peptide Onc112 inhibits translation by blocking and destabilizing the initiation complex. Nat Struct Mol Biol 2015; 22:470-5. [PMID: 25984971 DOI: 10.1038/nsmb.3034] [Citation(s) in RCA: 133] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 04/22/2015] [Indexed: 01/05/2023]
Abstract
The increasing prevalence of multidrug-resistant pathogenic bacteria is making current antibiotics obsolete. Proline-rich antimicrobial peptides (PrAMPs) display potent activity against Gram-negative bacteria and thus represent an avenue for antibiotic development. PrAMPs from the oncocin family interact with the ribosome to inhibit translation, but their mode of action has remained unclear. Here we have determined a structure of the Onc112 peptide in complex with the Thermus thermophilus 70S ribosome at a resolution of 3.1 Å by X-ray crystallography. The Onc112 peptide binds within the ribosomal exit tunnel and extends toward the peptidyl transferase center, where it overlaps with the binding site for an aminoacyl-tRNA. We show biochemically that the binding of Onc112 blocks and destabilizes the initiation complex, thus preventing entry into the elongation phase. Our findings provide a basis for the future development of this class of potent antimicrobial agents.
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Carlier L, Joanne P, Khemtémourian L, Lacombe C, Nicolas P, El Amri C, Lequin O. Investigating the role of GXXXG motifs in helical folding and self-association of plasticins, Gly/Leu-rich antimicrobial peptides. Biophys Chem 2015; 196:40-52. [DOI: 10.1016/j.bpc.2014.09.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Revised: 09/16/2014] [Accepted: 09/19/2014] [Indexed: 12/24/2022]
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Ng DP, Deber CM. Terminal residue hydrophobicity modulates transmembrane helix-helix interactions. Biochemistry 2014; 53:3747-57. [PMID: 24857611 DOI: 10.1021/bi500317h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Central to the formation of tertiary structure in membrane protein folding is the presence of amino acid sequence motifs (such as "small-XXX-small" segments) in the TM segments that promote interaction-compatible surfaces through which the TM α-helices interact. Here, we sought to elucidate additional factors that may work in tandem to dictate the ultimate interaction fate of TM-embedded segments. In this context, we used proteolipid protein (PLP), the major protein from central nervous system myelin for which mutant-dependent non-native oligomerization has been implicated in neurological disorders, to explore the specific effects of TM boundary residues (the membrane entry and exit points), keying on the secondary structure and self-association of peptides corresponding to the PLP TM2 α-helix (wild-type sequence ⁶⁶AFQYVIYGTASFFFLYGALLLAEGF⁹⁰). Using gel electrophoresis, circular dichroism, and Förster resonance energy transfer in the membrane-mimetic detergent sodium dodecyl sulfate (SDS), we found that mutation of F90 to residues such as A, I, L, or V maintains the onset of TM2-TM2 dimerization, whereas mutation to E, G, Q, N, S, or T abrogates dimer formation. We attribute this sensitivity to changes in local hydrophobicity, viz., a decrease in hydrophobicity reduces local lipid-peptide interactions, which in turn disrupts peptide α-helicity and hence the effectiveness of an incipient interaction-compatible surface. Our results show that the secondary structure and oligomeric state of PLP TM2 Lys-tagged peptides are significantly modulated by the specific nature of their C-terminal boundary residue, thus providing insight as to how point mutations, particularly where they produce disease states, can compromise the folding process.
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Affiliation(s)
- Derek P Ng
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children , Toronto, Ontario M5G 0A4, Canada
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Caillon L, Killian JA, Lequin O, Khemtémourian L. Biophysical investigation of the membrane-disrupting mechanism of the antimicrobial and amyloid-like peptide dermaseptin S9. PLoS One 2013; 8:e75528. [PMID: 24146759 PMCID: PMC3795727 DOI: 10.1371/journal.pone.0075528] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 08/14/2013] [Indexed: 12/16/2022] Open
Abstract
Dermaseptin S9 (Drs S9) is an atypical cationic antimicrobial peptide with a long hydrophobic core and with a propensity to form amyloid-like fibrils. Here we investigated its membrane interaction using a variety of biophysical techniques. Rather surprisingly, we found that Drs S9 induces efficient permeabilisation in zwitterionic phosphatidylcholine (PC) vesicles, but not in anionic phosphatidylglycerol (PG) vesicles. We also found that the peptide inserts more efficiently in PC than in PG monolayers. Therefore, electrostatic interactions between the cationic Drs S9 and anionic membranes cannot explain the selectivity of the peptide towards bacterial membranes. CD spectroscopy, electron microscopy and ThT fluorescence experiments showed that the peptide adopts slightly more β-sheet and has a higher tendency to form amyloid-like fibrils in the presence of PC membranes as compared to PG membranes. Thus, induction of leakage may be related to peptide aggregation. The use of a pre-incorporation protocol to reduce peptide/peptide interactions characteristic of aggregates in solution resulted in more α-helix formation and a more pronounced effect on the cooperativity of the gel-fluid lipid phase transition in all lipid systems tested. Calorimetric data together with 2H- and 31P-NMR experiments indicated that the peptide has a significant impact on the dynamic organization of lipid bilayers, albeit slightly less for zwitterionic than for anionic membranes. Taken together, our data suggest that in particular in membranes of zwitterionic lipids the peptide binds in an aggregated state resulting in membrane leakage. We propose that also the antimicrobial activity of Drs S9 may be a result of binding of the peptide in an aggregated state, but that specific binding and aggregation to bacterial membranes is regulated not by anionic lipids but by as yet unknown factors.
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Affiliation(s)
- Lucie Caillon
- UPMC Univ Paris 06, UMR 7203 CNRS-UPMC-ENS, Laboratoire des Biomolécules, Paris, France
| | - J. Antoinette Killian
- Research Group Membrane Biochemistry & Biophysics, Bijvoet Center and Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands
| | - Olivier Lequin
- UPMC Univ Paris 06, UMR 7203 CNRS-UPMC-ENS, Laboratoire des Biomolécules, Paris, France
- * E-mail: (LK); (OL)
| | - Lucie Khemtémourian
- UPMC Univ Paris 06, UMR 7203 CNRS-UPMC-ENS, Laboratoire des Biomolécules, Paris, France
- * E-mail: (LK); (OL)
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Beevers AJ, Nash A, Salazar-Cancino M, Scott DJ, Notman R, Dixon AM. Effects of the Oncogenic V664E Mutation on Membrane Insertion, Structure, and Sequence-Dependent Interactions of the Neu Transmembrane Domain in Micelles and Model Membranes: An Integrated Biophysical and Simulation Study. Biochemistry 2012; 51:2558-68. [DOI: 10.1021/bi201269w] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | | | | | - David J. Scott
- Department of Biosciences, University of Nottingham, Nottingham, U.K
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Prakash A, Janosi L, Doxastakis M. GxxxG motifs, phenylalanine, and cholesterol guide the self-association of transmembrane domains of ErbB2 receptors. Biophys J 2012; 101:1949-58. [PMID: 22004749 DOI: 10.1016/j.bpj.2011.09.017] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Revised: 08/30/2011] [Accepted: 09/15/2011] [Indexed: 11/28/2022] Open
Abstract
GxxxG motifs are common in transmembrane domains of membrane proteins and are often introduced to artificial peptides to inhibit or promote association to stable structures. The transmembrane domain of ErbB2 presents two separate such motifs that are proposed to be connected to stability and activity of the dimer. Using molecular simulations, we show that these sequences play a critical role during the recognition stage, forming transient complexes that lead to stable dimers. In pure phospholipid bilayers association occurs by contacts formed at the C-terminus promoted by the presence of phenylalanine residues. Helices subsequently rotate to eventually pack at short separations favored by lipid entropic contributions. In contrast, at intermediate cholesterol concentrations, a different pathway is followed that involves dimers with a weaker interface toward the N-terminus. However, at high cholesterol content, a switch toward the C-terminus is observed with an overall nonmonotonic change of the dimerization affinity. This conformational switch modulated by cholesterol has important implications on the thermodynamic, structural, and kinetic characteristics of helix-helix association in lipid membranes.
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Affiliation(s)
- Anupam Prakash
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas, USA
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Cymer F, Schneider D. Transmembrane helix-helix interactions involved in ErbB receptor signaling. Cell Adh Migr 2010; 4:299-312. [PMID: 20212358 DOI: 10.4161/cam.4.2.11191] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Among the many transmembrane receptor classes, the receptor tyrosine kinases represent an important superfamily, involved in many cellular processes like embryogenesis, development and cell division. Deregulation and dysfunctions of these receptors can lead to various forms of cancer and other diseases. Mostly, only fragmented knowledge exists about functioning of the entire receptors, and many studies have been performed on isolated receptor domains. In this review we focus on the function of the ErbB family of receptor tyrosine kinases with a special emphasis on the role of the transmembrane domain and on the mechanisms underlying regulated and deregulated signaling. Many general aspects of ErbB receptor structure and function have been analyzed and described. All human ErbBs appear to form homo- and heterodimers within cellular membranes and the single transmembrane domain of the receptors is involved in dimerization. Additionally, only defined structures of the transmembrane helix dimer allows signaling of ErbB receptors.
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Affiliation(s)
- Florian Cymer
- Albert-Ludwigs-University Freiburg, Department of Biochemistry and Molecular Biology, ZBMZ, and Fakultät für Biologie, Freiburg, Germany
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Beevers AJ, Damianoglou A, Oates J, Rodger A, Dixon AM. Sequence-Dependent Oligomerization of the Neu Transmembrane Domain Suggests Inhibition of “Conformational Switching” by an Oncogenic Mutant. Biochemistry 2010; 49:2811-20. [DOI: 10.1021/bi902087v] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Andrew J. Beevers
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K
| | | | - Joanne Oates
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K
| | - Alison Rodger
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K
| | - Ann M. Dixon
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K
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Bordag N, Keller S. α-Helical transmembrane peptides: A “Divide and Conquer” approach to membrane proteins. Chem Phys Lipids 2010; 163:1-26. [PMID: 19682979 DOI: 10.1016/j.chemphyslip.2009.07.009] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Revised: 07/21/2009] [Accepted: 07/21/2009] [Indexed: 11/26/2022]
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Reversible transition between α-helix and β-sheet conformation of a transmembrane domain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1722-30. [DOI: 10.1016/j.bbamem.2009.05.014] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2008] [Revised: 05/16/2009] [Accepted: 05/19/2009] [Indexed: 12/28/2022]
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Diller A, Loudet C, Aussenac F, Raffard G, Fournier S, Laguerre M, Grélard A, Opella SJ, Marassi FM, Dufourc EJ. Bicelles: A natural 'molecular goniometer' for structural, dynamical and topological studies of molecules in membranes. Biochimie 2009; 91:744-51. [PMID: 19248817 PMCID: PMC2899883 DOI: 10.1016/j.biochi.2009.02.003] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2008] [Accepted: 02/13/2009] [Indexed: 10/21/2022]
Abstract
Major biological processes occur at the biological membrane. One of the great challenges is to understand the function of chemical or biological molecules inside the membrane; as well of those involved in membrane trafficking. This requires obtaining a complete picture of the in situ structure and dynamics as well as the topology and orientation of these molecules in the membrane lipid bilayer. These led to the creation of several innovative models of biological membranes in order to investigate the structure and dynamics of amphiphilic molecules, as well as integral membrane proteins having single or multiple transmembrane segments. Because the determination of the structure, dynamics and topology of molecules in membranes requires a macroscopic alignment of the system, a new membrane model called 'bicelles' that represents a crossover between lipid vesicles and classical micelles has become very popular due to its property of spontaneous self-orientation in magnetic fields. In addition, crucial factors involved in mimicking natural membranes, such as sample hydration, pH and salinity limits, are easy to control in bicelle systems. Bicelles are composed of mixtures of long chain (14-18 carbons) and short chain phospholipids (6-8 carbons) hydrated up to 98% with buffers and may adopt various morphologies depending on lipid composition, temperature and hydration. We have been developing bicelle systems under the form of nano-discs made of lipids with saturated or biphenyl-containing fatty acyl chains. Depending on the lipid nature, these membranous nano-discs may be macroscopically oriented with their normal perpendicular or parallel to the magnetic field, providing a natural 'molecular goniometer' for structural and topological studies, especially in the field of NMR. Bicelles can also be spun at the magic angle and lead to the 3D structural determination of molecules in membranes.
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Affiliation(s)
- Anna Diller
- CBMN UMR 5248, CNRS, Université Bordeaux, ENITAB, IECB, 2, rue Robert Escarpit, 33607 Pessac, France
| | - Cécile Loudet
- The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | | | - Gérard Raffard
- RMSB UMR 5536, CNRS, Université Bordeaux, Bordeaux, France
| | - Sylvie Fournier
- CBMN UMR 5248, CNRS, Université Bordeaux, ENITAB, IECB, 2, rue Robert Escarpit, 33607 Pessac, France
| | - Michel Laguerre
- CBMN UMR 5248, CNRS, Université Bordeaux, ENITAB, IECB, 2, rue Robert Escarpit, 33607 Pessac, France
| | - Axelle Grélard
- CBMN UMR 5248, CNRS, Université Bordeaux, ENITAB, IECB, 2, rue Robert Escarpit, 33607 Pessac, France
| | - Stanley J. Opella
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0307, USA
| | | | - Erick J. Dufourc
- CBMN UMR 5248, CNRS, Université Bordeaux, ENITAB, IECB, 2, rue Robert Escarpit, 33607 Pessac, France
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