51
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Contera SA, Lemaître V, de Planque MRR, Watts A, Ryan JF. Unfolding and extraction of a transmembrane alpha-helical peptide: dynamic force spectroscopy and molecular dynamics simulations. Biophys J 2005; 89:3129-40. [PMID: 16085762 PMCID: PMC1366810 DOI: 10.1529/biophysj.105.061721] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
An atomic force microscope (AFM) was used to visualize CWALP(19)23 peptides ((+)H(3)N-ACAGAWWLALALALALALALWWA-COO(-)) inserted in gel-phase DPPC and DSPC bilayers. The peptides assemble in stable linear structures and domains. A model for the organization of the peptides is given from AFM images and a 20 ns molecular dynamics (MD) simulation. Gold-coated AFM cantilevers were used to extract single peptides from the bilayer through covalent bonding to the cystein residue. Experimental and simulated force curves show two distinct force maxima. In the simulations these two maxima correspond to the extraction of the two pairs of tryptophan residues from the membrane. Unfolding of the peptide precedes extraction of the second distal set of tryptophans. To probe the energies involved, AFM force curves were obtained from 10 to 10(4) nm/s and MD force curves were simulated with 10(8)-10(11) nm/s pulling velocities (V). The velocity relationship with the force, F, was fitted to two fluctuation adhesive potential models. The first assumes the pulling produces a constant bias in the potential and predicts an F approximately ln (V) relationship. The second takes into account the ramped bias that the linker feels as it is being driven out of the adhesion complex and scales as F approximately (ln V)2/3.
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Affiliation(s)
- Sonia Antoranz Contera
- Bionanotechnology IRC, Physics Department, University of Oxford, Oxford OX1 3PU, United Kingdom.
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52
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Roes S, Seydel U, Gutsmann T. Probing the properties of lipopolysaccharide monolayers and their interaction with the antimicrobial peptide polymyxin B by atomic force microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:6970-8. [PMID: 16008411 DOI: 10.1021/la048218c] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
In contrast to the majority of all known cell types, Gram-negative bacteria have a second membrane, the outer membrane, which is an asymmetric bilayer composed of a phospholipid inner leaflet and a glycolipid outer leaflet. The glycolipid layer, in most cases being composed of a lipopolysaccharide (LPS), is the first target for antimicrobial agents. To get a basic understanding of the membrane-forming properties of LPS, we reconstituted monolayers of deep rough mutant LPS from Salmonella enterica serova Minnesota (R595 LPS), its lipid A moiety, and of the synthetic tetraacyl compound 406 (resembling the biosynthetic lipid A precursor IVa) at the air-water interface of a film balance. The liquid-expanded (LE) and liquid-condensed (LC) domains in the coexisting region were investigated with epifluorescence and, after transferring the monolayer onto mica, as a Langmuir-Blodgett film, with atomic force microscopy (AFM). The fluorescence and the AFM images showed identical domain structure. The higher resolution of the AFM images, however, contained more topographic details. Different heights and adhesion forces between the LE and LC domains could be observed. Differences in the adhesion forces between the AFM tip and the sample were determined in the repulsive and the attractive dynamic scanning modes, demonstrating the importance of a careful interpretation of height images. We propose that an increase in the lateral pressure causing the LE-LC transition of the monolayers leads to a reorientation of the molecules due to a tilt angle between the alkyl chains and the diglucosamine backbone. LPS monolayers have been utilized as a simplified reconstitution model of the outer membrane to study the interaction with antimicrobial agents. We investigated the action of the polycationic peptide polymyxin B (PMB) and found dramatic influences on the domain structures.
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Affiliation(s)
- Stefanie Roes
- Department of Immunochemistry and Biochemical Microbiology, Division of Biophysics, Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Parkallee 10, D-23845 Borstel, Germany
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53
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Merino S, Domènech O, Viñas M, Montero MT, Hernández-Borrell J. Effects of lactose permease on the phospholipid environment in which it is reconstituted: a fluorescence and atomic force microscopy study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:4642-7. [PMID: 16032883 DOI: 10.1021/la047102d] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The membrane transport protein lactose permease (LacY), a member of the major facilitator superfamily containing 12 membrane-spanning segments connected by hydrophilic loops, was reconstituted in liposomes whose composition was 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol in a 3:1 molar ratio. The structural order of the lipid membranes, in the presence and absence of LacY, was assessed using steady-state fluorescence anisotropy. The features of the anisotropy curves obtained with 1,6-phenyl-1,3,5-hexatriene and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate suggest a surface effect of LacY on the membranes. Atomic force microscopy imaging of supported planar bilayers (SPBs) deposited onto mica was used to examine the effect of LacY on the nanostructure of the phospholipid matrix. Two separated domains were observed in SPBs formed from pure phospholipid mixture. Protein assemblies segregated from the rest of the matrix were observed after the extension of proteoliposomes. The effect of the protein on the electrostatic surface potential of the bilayer was also examined using a fluorescent pH indicator, 4-heptadecyl-7-hydroxycoumarin. Changes in surface potential were enhanced in the presence of the substrate (i.e., lactose). Taken together the results indicate that LacY is segregated into the phospholipid matrix and has moderate effects on the acyl chain order of the bilayers. The changes in surface electrical properties of the bilayers suggest a role for the phospholipid headgroups in proton transfer to the amino acids involved in substrate translocation.
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Affiliation(s)
- Sandra Merino
- Departament de Fisicoquímica and Química Física, Universitat de Barcelona, E-08028 Barcelona, Spain
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54
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Hinz A, Galla HJ. Viral membrane penetration: lytic activity of a nodaviral fusion peptide. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2005; 34:285-93. [PMID: 15834560 DOI: 10.1007/s00249-004-0450-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2004] [Revised: 11/19/2004] [Accepted: 11/22/2004] [Indexed: 11/30/2022]
Abstract
The auto-cleavage product from the C-terminal part of the capsid protein of the flock house virus, namely the gamma(1) peptide, was used as a model peptide to characterize the initial steps of viral membrane penetration. Monolayers at the air-water interface were used to investigate the phase behaviour of ternary lipid-peptide mixtures, whereas solid-supported membranes were used to visualize the lytic activity of the gamma(1) peptide. 1,2-Dipalmitoyl-sn-glycero-phospatidylcholine/1,2-dipalmitoyl-sn-glycero-phospatidylserine (4:1) membranes were used as negatively charged model membranes. By means of film balance techniques lipid/peptide discrimination was found resulting in a lipid-rich and a peptide-rich phase. Quartz crystal microbalance and scanning force microscopy experiments led to the conclusion of a detergent-like mechanism of the gamma(1) peptide resulting in mixed lipid-peptide micelles with a molar ratio of 2.8:1. A monolayer adsorption with an ongoing lysis of membranes was found with gamma(1) peptide molecules interacting at membrane defects.
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Affiliation(s)
- Andreas Hinz
- Institut für Biochemie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 2, 48149 Münster, Germany.
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55
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El Kirat K, Lins L, Brasseur R, Dufrêne YF. Fusogenic tilted peptides induce nanoscale holes in supported phosphatidylcholine bilayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:3116-3121. [PMID: 15779993 DOI: 10.1021/la047640q] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Tilted peptides are known to insert in lipid bilayers with an oblique orientation, thereby destabilizing membranes and facilitating membrane fusion processes. Here, we report the first direct visualization of the interaction of tilted peptides with lipid membranes using in situ atomic force microscopy (AFM) imaging. Phase-separated supported dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DOPC/DPPC) bilayers were prepared by fusion of small unilamellar vesicles and imaged in buffer solution, in the absence and in the presence of the simian immunodeficiency virus (SIV) peptide. The SIV peptide was shown to induce the rapid appearance of nanometer scale bilayer holes within the DPPC gel domains, while keeping the domain shape unaltered. We attribute this behavior to a local weakening and destabilization of the DPPC domains due to the oblique insertion of the peptide molecules. These results were directly correlated with the fusogenic activity of the peptide as determined using fluorescently labeled DOPC/DPPC liposomes. By contrast, the nontilted ApoE peptide did not promote liposome fusion and did not induce bilayer holes but caused slight erosion of the DPPC domains. In conclusion, this work provides the first direct evidence for the production of stable, well-defined nanoholes in lipid bilayer domains by the SIV peptide, a behavior that we have shown to be specifically related to the tilted character of the peptide. A molecular mechanism underlying spontaneous insertion of the SIV peptide within lipid bilayers and the subsequent removal of bilayer patches is proposed, and its relevance to membrane fusion processes is discussed.
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Affiliation(s)
- Karim El Kirat
- Unité de chimie des interfaces, Université catholique de Louvain, Croix du Sud 2/18, B-1348 Louvain-la-Neuve, Belgium
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56
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Orädd G, Lindblom G. NMR Studies of lipid lateral diffusion in the DMPC/gramicidin D/water system: peptide aggregation and obstruction effects. Biophys J 2005; 87:980-7. [PMID: 15298904 PMCID: PMC1304505 DOI: 10.1529/biophysj.103.038828] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The PFG-NMR method has been used in macroscopically oriented bilayers to investigate the effect of the peptide gramicidin D on the lateral diffusion of dimyristoylphosphatidylcholine. By varying both the temperature (21-35 degrees C) and the gramicidin content (0-5 mol %) we have introduced solid obstacles into the lipid liquid crystalline bilayer. It was shown that the obstruction effect exerted by the peptide can be described with several different theoretical models, each based on different premises, and that the fit of the models to experimental data gave reasonable results. We found that each gramicidin molecule was surrounded by approximately one layer of bound lipids and that the obstruction from gel phase patches can be described as small solid obstacles. No evidence of linear aggregates of gramicidin, such as those reported by atomic force microscopy in the gel phase, was found.
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Affiliation(s)
- Greger Orädd
- Department of Biophysical Chemistry, Umeå University, Umeå, Sweden.
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57
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Micelli S, Meleleo D, Picciarelli V, Stoico MG, Gallucci E. Effect of nanomolar concentrations of sodium dodecyl sulfate, a catalytic inductor of alpha-helices, on human calcitonin incorporation and channel formation in planar lipid membranes. Biophys J 2005; 87:1065-75. [PMID: 15298911 PMCID: PMC1304447 DOI: 10.1529/biophysj.103.037200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human Calcitonin (hCt) is a peptide hormone which has a regulatory action in calcium-phosphorus metabolism. It is currently used as a therapeutic tool in bone pathologies such as osteoporosis and Paget's disease. However, due to its amphiphilic property tends to form a gelatinous solution in water which consists of fibrils that limits its therapeutic use. Here we show that sodium dodecyl sulfate (SDS), an anionic detergent able to induce and stabilize alpha-helices in polypeptides, at a monomeric concentration ranging between 0.26 mM-5 pM (all concentrations are below the CMC), increases the rate and number of hCt channel formation in planar lipid membranes, at both high and low hCt concentrations, with a maximum increase at a molecular hCt/SDS ratio of 1000:1. This effect could be interpreted as a counteraction to the fibrillation process of hCt molecules by removing molecules available for aggregation from the fluid; furthermore, this action, independently of channel formation in the cell membrane, could improve the peptide-receptor interaction. The action of SDS could be attributable to the strength of the sulfate negative charge and the hydrophobic chain; in fact, a similar effect was obtained with lauryl sarcosine and not with a neutral detergent such as n-dodecyl-beta-D-maltoside. The very low molecular ratio between SDS and peptide is suggestive of a possible catalytic action of SDS that could induce alpha-helices, the appropriate structures for interacting with the membrane. Moreover, in the experimental conditions investigated, the addition of SDS does not modify the membrane's electrical properties and most of the channel properties. This finding may contribute to the knowledge of environment-folding diseases due to protein and peptides.
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Affiliation(s)
- Silvia Micelli
- Dipartimento Farmaco-Biologico, Dipartimento Interateneo di Fisica, Università degli Studi di Bari, I-70126 Bari, Italy
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58
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Strandberg E, Ozdirekcan S, Rijkers DTS, van der Wel PCA, Koeppe RE, Liskamp RMJ, Killian JA. Tilt angles of transmembrane model peptides in oriented and non-oriented lipid bilayers as determined by 2H solid-state NMR. Biophys J 2005; 86:3709-21. [PMID: 15189867 PMCID: PMC1304272 DOI: 10.1529/biophysj.103.035402] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Solid-state NMR methods employing (2)H NMR and geometric analysis of labeled alanines (GALA) were used to study the structure and orientation of the transmembrane alpha-helical peptide acetyl-GWW(LA)(8)LWWA-amide (WALP23) in phosphatidylcholine (PC) bilayers of varying thickness. In all lipids the peptide was found to adopt a transmembrane alpha-helical conformation. A small tilt angle of 4.5 degrees was observed in di-18:1-PC, which has a hydrophobic bilayer thickness that approximately matches the hydrophobic length of the peptide. This tilt angle increased slightly but systematically with increasing positive mismatch to 8.2 degrees in di-C12:0-PC, the shortest lipid used. This small increase in tilt angle is insufficient to significantly change the effective hydrophobic length of the peptide and thereby to compensate for the increasing hydrophobic mismatch, suggesting that tilt of these peptides in a lipid bilayer is energetically unfavorable. The tilt and also the orientation around the peptide axis were found to be very similar to the values previously reported for a shorter WALP19 peptide (GWW(LA)(6)LWWA). As also observed in this previous study, the peptide rotates rapidly around the bilayer normal, but not around its helix axis. Here we show that these properties allow application of the GALA method not only to macroscopically aligned samples but also to randomly oriented samples, which has important practical advantages. A minimum of four labeled alanine residues in the hydrophobic transmembrane sequence was found to be required to obtain accurate tilt values using the GALA method.
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Affiliation(s)
- Erik Strandberg
- Department of Biochemistry of Membranes, Center for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht, The Netherlands
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59
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Tong J, McIntosh TJ. Structure of supported bilayers composed of lipopolysaccharides and bacterial phospholipids: raft formation and implications for bacterial resistance. Biophys J 2005; 86:3759-71. [PMID: 15189872 PMCID: PMC1304277 DOI: 10.1529/biophysj.103.037507] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Lipopolysaccharide (LPS), the major lipid on the surface of Gram-negative bacteria, plays a key role in bacterial resistance to hydrophobic antibiotics and antimicrobial peptides. Using atomic force microscopy (AFM) we characterized supported bilayers composed of LPSs from two bacterial chemotypes with different sensitivities to such antibiotics and peptides. Rd LPS, from more sensitive "deep rough" mutants, contains only an inner saccharide core, whereas Ra LPS, from "rough" mutants, contains a longer polysaccharide region. A vesicle fusion technique was used to deposit LPS onto either freshly cleaved mica or polyethylenimine-coated mica substrates. The thickness of the supported bilayers measured with contact-mode AFM was 7 nm for Rd LPS and 9 nm for Ra LPS, consistent with previous x-ray diffraction measurements. In water the Ra LPS bilayer surface was more disordered than Rd LPS bilayers, likely due to the greater volume occupied by the longer Ra LPS polysaccharide region. Since deep rough mutants contain bacterial phospholipid (BPL) as well as LPS on their surfaces, we also investigated the organization of Rd LPS/BPL bilayers. Differential scanning calorimetry and x-ray diffraction indicated that incorporation of BPL reduced the phase transition temperature, enthalpy, and average bilayer thickness of Rd LPS. For Rd LPS/BPL mixtures, AFM showed irregularly shaped regions thinner than Rd LPS bilayers by 2 nm (the difference in thickness between Rd LPS and BPL bilayers), whose area increased with increasing BPL concentration. We argue that the increased permeability of deep rough mutants is due to structural modifications caused by BPL to the LPS membrane, in LPS hydrocarbon chain packing and in the formation of BPL-enriched microdomains.
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Affiliation(s)
- Jihong Tong
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina, USA
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60
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Krishna G, Shutava T, Lvov Y. Lipid modified polyelectrolyte microcapsules with controlled diffusion. Chem Commun (Camb) 2005:2796-8. [PMID: 15928761 DOI: 10.1039/b415774e] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The lipid coating introduced directly on (polystyrene sulfonate/polyallylamine hydrochloride)5 polyelectrolyte microcapsule surfaces significantly reduces the permeability of capsule walls estimated by fluorescence recovery after photobleaching (FRAP).
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Affiliation(s)
- Gopal Krishna
- Institute for Micromanufacturing, Louisiana Tech University, 911 Hergot Ave, Ruston, LA 71272, USA
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61
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Abstract
As the number of membrane proteins in the Protein Data Bank increases, efforts to understand how they interact with their natural environment are increasing in importance. A number of membrane proteins crystallise with lipid molecules implicitly bound at discrete locations that are consistent with the transmembrane regions of the protein. Bioinformatics studies also point to the specific interactions of some amino acids with membrane lipids. The results of experiments using model systems are revealing how these interactions contribute to the stability of both the protein and the membrane in which it is embedded. From a different perspective, the processes involved in the binding of peptides to membrane surfaces to produce a variety of effects are being understood in ever-increasing detail. This review describes current research efforts and thinking in this area.
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Affiliation(s)
- John M Sanderson
- Centre for Bioactive Chemistry, Department of Chemistry, University Science Laboratories, Durham, UK DH1 3LE.
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62
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Kik RA, Leermakers FAM, Kleijn JM. Molecular modeling of lipid bilayers and the effect of protein-like inclusions. Phys Chem Chem Phys 2005; 7:1996-2005. [DOI: 10.1039/b501893e] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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63
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Plénat T, Deshayes S, Boichot S, Milhiet PE, Cole RB, Heitz F, Le Grimellec C. Interaction of primary amphipathic cell-penetrating peptides with phospholipid-supported monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2004; 20:9255-9261. [PMID: 15461515 DOI: 10.1021/la048622b] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The mesoscopic organization adopted by two primary amphipathic peptides, P(beta) and P(alpha), in Langmuir-Blodgett (LB) films made of either the pure peptide or peptide-phospholipid mixtures was examined by atomic force microscopy. P(beta), a potent cell-penetrating peptide (CPP), and P(alpha) mainly differ by their conformational states, predominantly a beta-sheet for P(beta) and an alpha-helix for P(alpha), as determined by Fourier transform infrared spectroscopy. LB films of pure peptide, transferred significantly below their collapse pressure, were characterized by the presence of supramolecular structures, globular aggregates for P(beta) and filaments for P(alpha), inserted into the monomolecular film. In mixed peptide-phospholipid films, similar structures could be observed, as a function of the phospholipid headgroup and acyl chain saturation. They often coexisted with a liquid-expanded phase composed of miscible peptide-lipid. These data strongly suggest that primary amphipathic CPP and antimicrobial peptides may share, to some extent, common mechanisms of interaction with membranes.
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Affiliation(s)
- Thomas Plénat
- Nanostructures et Complexes Membranaires, CBS, CNRS UMR5048-INSERM U554, 29 rue de Navacelles, 34090 Montpellier Cedex, France
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64
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Boichot S, Krauss U, Plénat T, Rennert R, Milhiet PE, Beck-Sickinger A, Le Grimellec C. Calcitonin-derived carrier peptide plays a major role in the membrane localization of a peptide-cargo complex. FEBS Lett 2004; 569:346-50. [PMID: 15225660 DOI: 10.1016/j.febslet.2004.05.078] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2004] [Revised: 05/18/2004] [Accepted: 05/18/2004] [Indexed: 10/26/2022]
Abstract
Bilayers made of dioleoylphosphatidylcholine (DOPC)/dipalmitoylphosphatidylcholine (DPPC) mixture containing or not cholesterol (Chl) were used to investigate the interaction of a carrier peptide with membranes. Atomic force microscopy revealed that the C-terminal 9-32 fragment of human calcitonin (hCT (9-32)), free or coupled to enhanced green fluorescent protein (hCT-eGFP) cargo forms aggregates in the DOPC fluid phase in absence of Chl and in the DPPC enriched liquid-ordered phase when Chl is present. The data show that hCT (9-32) plays a determinant role in the membrane localization of the peptide-cargo complex. They suggest that carpet-like mechanism for membrane destabilization may be involved in the carrier function of hCT (9-32).
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Affiliation(s)
- Sylvie Boichot
- Nanostructures et Complexes Membranaires, C.B.S. CNRS UMR5048-INSERM U554, 29 rue de Navacelles, 34090 Montpellier Cedex, France
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65
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Orädd G, Lindblom G. Lateral diffusion studied by pulsed field gradient NMR on oriented lipid membranes. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2004; 42:123-131. [PMID: 14745791 DOI: 10.1002/mrc.1338] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
This mini-review focuses on the utilization of pulsed magnetic field gradients to measure diffusional motion in systems of macroscopically oriented lipid bilayers. The NMR diffusion technique is proposed to have appreciable potential for future biophysical investigations in the field of membrane biology. Topics such as transport of molecules both across and in the plane of the membrane can be successfully studied, and the formation of lipid domains and their intrinsic dynamics can also be scrutinized. First, a short introduction to the NMR technique is given together with a brief discussion on methods of obtaining a good bilayer orientation. Then, a number of recent results on biophysical/biological membrane systems of great interest is presented, in which some unique conclusions on so-called 'raft membranes' are reached. It is shown for systems with large two-phase areas of liquid disordered and liquid ordered phases that lipid lateral diffusion is faster in the former phase and has a smaller apparent activation energy. Further, on the time-scale of the experiments (50-250 ms), exchange between the two phases is fast in the phospholipid-cholesterol-water ternary system, whereas it is slow in the sphingomyelin-dioleoylphosphatidylcholine-cholesterol-water quaternary system.
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Affiliation(s)
- Greger Orädd
- Department of Biophysical Chemistry, Umeå University, Umeå, Sweden
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66
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Abstract
There are many ways in which lipids can modulate the activity of membrane proteins. Simply a change in hydrophobic thickness of the lipid bilayer, for example, already can have various consequences for membrane protein organization and hence for activity. By using synthetic transmembrane peptides, it could be established that these consequences include peptide oligomerization, tilt of transmembrane segments, and reorientation of side chains, depending on the specific properties of the peptides and lipids used. The results illustrate the potential of the use of synthetic model peptides to establish general principles that govern interactions between membrane proteins and surrounding lipids.
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Affiliation(s)
- J Antoinette Killian
- Department of Biochemistry of Membranes, Center for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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67
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Vogel A, Scheidt HA, Huster D. The distribution of lipid attached spin probes in bilayers: application to membrane protein topology. Biophys J 2003; 85:1691-701. [PMID: 12944284 PMCID: PMC1303343 DOI: 10.1016/s0006-3495(03)74599-8] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The distribution of the lipid-attached doxyl electron paramagnetic resonance (EPR) spin label in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes has been studied by (1)H and (13)C magic angle spinning nuclear magnetic resonance relaxation measurements. The doxyl spin label was covalently attached to the 5th, 10th, and 16th carbons of the sn-2 stearic acid chain of a 1-palmitoyl-2-stearoyl-(5/10/16-doxyl)-sn-glycero-3-phosphocholine analog. Due to the unpaired electron of the spin label, (1)H and (13)C lipid relaxation rates are enhanced by paramagnetic relaxation. For all lipid segments the influence of paramagnetic relaxation is observed even at low probe concentrations. Paramagnetic relaxation rates provide a measure for the interaction strength between lipid segments and the doxyl group. Plotted along the membrane director a transverse distribution profile of the EPR probe is obtained. The chain-attached spin labels are broadly distributed in the membrane with a maximum at the approximate chain position of the probe. Both (1)H and (13)C relaxation measurements show these broad distributions of the doxyl group in the membrane indicating that (1)H spin diffusion does not influence the relaxation measurements. The broad distributions of the EPR label result from the high degree of mobility and structural heterogeneity in liquid-crystalline membranes. Knowing the distribution profiles of the EPR probes, their influence on relaxation behavior of membrane inserted peptide and protein segments can be studied by (13)C magic angle spinning nuclear magnetic resonance. As an example, the location of Ala residues positioned at three sites of the transmembrane WALP-16 peptide was investigated. All three doxyl-labeled phospholipid analogs induce paramagnetic relaxation of the respective Ala site. However, for well ordered secondary structures the strongest relaxation enhancement is observed for that doxyl group in the closest proximity to the respective Ala. Thus, this approach allows study of membrane insertion of protein segments with respect to the high molecular mobility in liquid-crystalline membranes.
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Affiliation(s)
- Alexander Vogel
- Junior Research Group Solid-state NMR Studies of the Structure of Membrane-associated Proteins, Biotechnological-Biomedical Center, Institute of Medical Physics and Biophysics, University of Leipzig, D-04103 Leipzig, Germany
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68
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Gómez-Treviño A, Castel S, López-Iglesias C, Cortadellas N, Comas-Riu J, Mercadé E. Effects of adenovirus-mediated SV5 fusogenic glycoprotein expression on tumor cells. J Gene Med 2003; 5:483-92. [PMID: 12797113 DOI: 10.1002/jgm.371] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND The fusogenic (F) membrane glycoprotein of the paramyxovirus SV5 allows virus to enter host cells and mediates fusion between neighboring cells, which leads to cell death. F glycoprotein is synthesized as an inactive precursor (F(0)) that is cleaved by cellular protease furine to form the active heterodimer F(1) + F(2). The active protein can induce syncytium formation in the absence of another integral glycoprotein (HN), a property that appears to be unique among paramyxoviruses. METHODOLOGY We constructed a non-replicative adenovirus to express SV5 F protein in tumor cells, and its fusion capacity was analyzed by fluorescent and confocal microscopy. Cell viability and bystander effect were compared with the thymidine kinase/ganciclovir suicide gene therapy. The structure of F-expressing cells was studied using electron microscopy. RESULTS F glycoprotein expression induced syncytium formation to a maximum at 72 h, after which syncytia progressively lost viability and detached. The cell membrane was disrupted while nuclear structure was preserved. Over-expression of SV5 F protein in tumor cells led to high cytotoxicity comparable with that associated with the thymidine kinase/ganciclovir. A potent bystander killing effect was detected until the ratio of F-transduced to non-transduced cells was 1 : 100. CONCLUSIONS These results indicate that the fusogenic glycoprotein of the paramyxovirus SV5 could be used to eliminate tumor cells and may encourage studies aimed at modifying its selectivity and combining its expression with other cytotoxic strategies to improve their efficacy.
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Affiliation(s)
- A Gómez-Treviño
- Department of Microbiology, University of Barcelona, 08028 Barcelona, Spain
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69
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Lee AG. Lipid-protein interactions in biological membranes: a structural perspective. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1612:1-40. [PMID: 12729927 DOI: 10.1016/s0005-2736(03)00056-7] [Citation(s) in RCA: 636] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Lipid molecules bound to membrane proteins are resolved in some high-resolution structures of membrane proteins. An analysis of these structures provides a framework within which to analyse the nature of lipid-protein interactions within membranes. Membrane proteins are surrounded by a shell or annulus of lipid molecules, equivalent to the solvent layer surrounding a water-soluble protein. The lipid bilayer extends right up to the membrane protein, with a uniform thickness around the protein. The surface of a membrane protein contains many shallow grooves and protrusions to which the fatty acyl chains of the surrounding lipids conform to provide tight packing into the membrane. An individual lipid molecule will remain in the annular shell around a protein for only a short period of time. Binding to the annular shell shows relatively little structural specificity. As well as the annular lipid, there is evidence for other lipid molecules bound between the transmembrane alpha-helices of the protein; these lipids are referred to as non-annular lipids. The average thickness of the hydrophobic domain of a membrane protein is about 29 A, with a few proteins having significantly smaller or greater thicknesses than the average. Hydrophobic mismatch between a membrane protein and the surrounding lipid bilayer generally leads to only small changes in membrane thickness. Possible adaptations in the protein to minimise mismatch include tilting of the helices and rotation of side chains at the ends of the helices. Packing of transmembrane alpha-helices is dependent on the chain length of the surrounding phospholipids. The function of membrane proteins is dependent on the thickness of the surrounding lipid bilayer, sometimes on the presence of specific, usually anionic, phospholipids, and sometimes on the phase of the phospholipid.
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Affiliation(s)
- A G Lee
- Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Bassett Crescent East, SO16 7PX, Southampton, UK.
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70
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Ivanova VP, Makarov IM, Schäffer TE, Heimburg T. Analyzing heat capacity profiles of peptide-containing membranes: cluster formation of gramicidin A. Biophys J 2003; 84:2427-39. [PMID: 12668450 PMCID: PMC1302808 DOI: 10.1016/s0006-3495(03)75047-4] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The analysis of peptide and protein partitioning in lipid membranes is of high relevance for the understanding of biomembrane function. We used statistical thermodynamics analysis to demonstrate the effect of peptide mixing behavior on heat capacity profiles of lipid membranes with the aim to predict peptide aggregation from c(P)-profiles. This analysis was applied to interpret calorimetric data on the interaction of the antibiotic peptide gramicidin A with lipid membranes. The shape of the heat capacity profiles was found to be consistent with peptide clustering in both gel and fluid phase. Applying atomic force microscopy, we found gramicidin A aggregates and established a close link between thermodynamics data and microscopic imaging. On the basis of these findings we described the effect of proteins on local fluctuations. It is shown that the elastic properties of the membrane are influenced in the peptide environment.
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Affiliation(s)
- V P Ivanova
- Membrane Biophysics and Thermodynamics Group, Max-Planck-Institute for Biophysical Chemistry, 37070 Göttingen, Germany
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71
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Grage SL, Wang J, Cross TA, Ulrich AS. Solid-state 19F-NMR analysis of 19F-labeled tryptophan in gramicidin A in oriented membranes. Biophys J 2002; 83:3336-50. [PMID: 12496101 PMCID: PMC1302409 DOI: 10.1016/s0006-3495(02)75334-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The response of membrane-associated peptides toward the lipid environment or other binding partners can be monitored by solid-state NMR of suitably labeled side chains. Tryptophan is a prominent amino acid in transmembrane helices, and its (19)F-labeled analogues are generally biocompatible and cause little structural perturbation. Hence, we use 5F-Trp as a highly sensitive NMR probe to monitor the conformation and dynamics of the indole ring. To establish this (19)F-NMR strategy, gramicidin A was labeled with 5F-Trp in position 13 or 15, whose chi(1)/chi(2) torsion angles are known from previous (2)H-NMR studies. First, the alignment of the (19)F chemical shift anisotropy tensor within the membrane was deduced by lineshape analysis of oriented samples. Next, the three principal axes of the (19)F chemical shift anisotropy tensor were assigned within the molecular frame of the indole ring. Finally, determination of chi(1)/chi(2) for 5F-Trp in the lipid gel phase showed that the side chain alignment differs by up to 20 degrees from its known conformation in the liquid crystalline state. The sensitivity gain of (19)F-NMR and the reduction in the amount of material was at least 10-fold compared with previous (2)H-NMR studies on the same system and 100-fold compared with (15)N-NMR.
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72
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Abstract
One of the major pathological features of Alzheimer's disease (AD) is the presence of extracellular amyloid plaques that are composed predominantly of the amyloid-beta peptide (Abeta). Diffuse plaques associated with AD are composed predominantly of Abeta42, whereas senile plaques contain both Abeta40 and Abeta42. Recently, it has been suggested that diffuse plaque formation is initiated as a plasma membrane-bound Abeta species and that Abeta42 is the critical component. In order to investigate this hypothesis, we have examined Abeta42-membrane interactions using in situ atomic force microscopy and fluorescence spectroscopy. Our studies demonstrate the association of Abeta42 with planar bilayers composed of total brain lipids, which results initially in peptide aggregation and then fibre formation. Modulation of the cholesterol content is correlated with the extent of Abeta42-assembly on the bilayer surface. Although Abeta42 was not visualized directly on cholesterol-depleted bilayers, fluorescence anisotropy and fluorimetry demonstrate Abeta42-induced membrane changes. Our results demonstrate that the composition of the lipid bilayer governs the outcome of Abeta interactions.
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Affiliation(s)
- Christopher M Yip
- Department of Chemical Engineering and Applied Chemistry, Institute for Biomaterials and Biomedical Engineering and Centre for Studies in Molecular Imaging, University of Toronto, Toronto, Ontario, Canada M5S 3G9
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73
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Morein S, Killian JA, Sperotto MM. Characterization of the thermotropic behavior and lateral organization of lipid-peptide mixtures by a combined experimental and theoretical approach: effects of hydrophobic mismatch and role of flanking residues. Biophys J 2002; 82:1405-17. [PMID: 11867456 PMCID: PMC1301942 DOI: 10.1016/s0006-3495(02)75495-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
A combined experimental and theoretical study was performed on a series of mixtures of dipalmitoylphosphatidylcholine (DPPC) and synthetic peptides to investigate their thermotropic behavior and lateral organization. The experimental study was based on differential scanning calorimetry (DSC) and phosphorous nuclear magnetic resonance ((31)P-NMR) techniques; the theoretical study was based on calculations on a microscopic molecular interaction model, where the lipid-peptide interaction is built on the hydrophobic matching principle. The chosen peptides, WALP and KALP, consist of a hydrophobic stretch, of variable length, of alternating leucine and alanine residues, flanked on both ends with tryptophan and lysine residues, respectively. By systematically varying the peptide hydrophobic length it was thus possible to explore different matching conditions between the peptide's hydrophobic length and the lipid bilayer hydrophobic thickness, and to investigate the potential role of flanking residues. The results show that both the WALP and the KALP peptides tend to favor the liquid-crystalline (or fluid) phase of the system; i.e., they tend to depress the main-transition temperature, T(m), of pure DPPC. However, the detailed effects of both peptides on the lateral phase behavior of the lipid-peptide system are dependent on the peptide length and the type of flanking residues. The results suggest that below T(m), the shortest among the WALP and KALP peptides induce gel-fluid phase separation in the system within an extensive temperature-composition region. The longer the hydrophobic length of the peptides is, the more narrow this region appears to become.
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Affiliation(s)
- Sven Morein
- Department of Biochemistry of Membranes, Utrecht University, NL-3584 CH Utrecht, The Netherlands
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74
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Abstract
The introduction of functional imaging tools and techniques that operate at molecular-length scales has provided investigators with unique approaches to characterizing biomolecular structure and function relationships. Recent advances in the field of scanning probe techniques and, in particular, atomic force microscopy have yielded tantalizing insights into the dynamics of protein self-assembly and the mechanics of protein unfolding.
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Affiliation(s)
- C M Yip
- Department of Chemical Engineering, Institute of Biomaterials and Biomedical Engineering, University of Toronto, Ontario, Canada.
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75
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Abstract
Lateral segregation in biomembranes can lead to the formation of biologically functional domains. This paper reviews atomic force microscopy studies on domain formation in model membranes, with special emphasis on transbilayer asymmetry, and on lateral domains induced by lipid-lipid interactions or by peptide-lipid interactions.
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Affiliation(s)
- H A Rinia
- Department of Biochemistry of Membranes, CBLE, Institute of Biopmembranes, Utrecht university, Netherlands.
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76
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You HX, Yu L, Qi X. Phospholipid membrane restructuring induced by saposin C: a topographic study using atomic force microscopy. FEBS Lett 2001; 503:97-102. [PMID: 11513862 DOI: 10.1016/s0014-5793(01)02700-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The enzymatic activity of glucosylceramidase depends on the presence of saposin C (Sap C) and acidic phospholipid-containing membranes. In order to delineate the mechanism underlying Sap C stimulation of the enzyme activity, it is important to understand how Sap C interacts with phospholipid membranes. We studied the dynamic process of Sap C interaction with planar phospholipid membranes, in real time, using atomic force microscopy (AFM). The phospholipid membrane underwent restructuring upon addition of Sap C. The topographic characteristics of the membrane restructuring include the appearance of patch-like new features, initially emerged at the edge of phospholipid membranes and extended laterally with time. Changes in the image contrast of the phospholipid membrane observed after the Sap C addition indicate that a new phase of lipid-protein structure has formed during membrane restructuring. The process of membrane restructuring is dynamic, commencing shortly after Sap C addition, and continuing throughout the duration of AFM imaging (about 30 min, sometimes over 1 h). This study demonstrated the potential of AFM real-time imaging in studying protein-membrane interactions.
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Affiliation(s)
- H X You
- Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, OH 45267-0521, USA.
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77
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Rinia HA, Snel MM, van der Eerden JP, de Kruijff B. Visualizing detergent resistant domains in model membranes with atomic force microscopy. FEBS Lett 2001; 501:92-6. [PMID: 11457463 DOI: 10.1016/s0014-5793(01)02636-9] [Citation(s) in RCA: 231] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Evidence is accumulating that in cell membranes microdomains exist, also referred to as rafts or detergent resistant membranes. In this study, atomic force microscopy is used to study supported lipid bilayers, consisting of a fluid phosphatidylcholine, sphingomyelin and cholesterol. Domains were visualized of which the morphology and size depended on the cholesterol concentration. The presence of cholesterol was found to induce bilayer coupling. At 30 mol% cholesterol, a change in percolation phase was observed, and at 50 mol%, when both fluid lipids and solid lipids are saturated with cholesterol, phase separation was still observed. In addition, we were able to directly visualize the resistance of domains against non-ionic detergent.
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Affiliation(s)
- H A Rinia
- Department of Biochemistry of Membranes, CBLE, Institute of Biomembranes, Utrecht University, The Netherlands.
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Harms GS, Cognet L, Lommerse PH, Blab GA, Schmidt T. Autofluorescent proteins in single-molecule research: applications to live cell imaging microscopy. Biophys J 2001; 80:2396-408. [PMID: 11325739 PMCID: PMC1301428 DOI: 10.1016/s0006-3495(01)76209-1] [Citation(s) in RCA: 177] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The spectral and photophysical characteristics of the autofluorescent proteins were analyzed and compared to flavinoids to test their applicability for single-molecule microscopy in live cells. We compare 1) the number of photons emitted by individual autofluorescent proteins in artificial and in vivo situations, 2) the saturation intensities of the various autofluorescent proteins, and 3) the maximal emitted photons from individual fluorophores in order to specify their use for repetitive imaging and dynamical analysis. It is found that under relevant conditions and for millisecond integration periods, the autofluorescent proteins have photon emission rates of approximately 3000 photons/ms (with the exception of DsRed), saturation intensities from 6 to 50 kW/cm2, and photobleaching yields from 10(-4) to 10(-5). Definition of a detection ratio led to the conclusion that the yellow-fluorescent protein mutant eYFP is superior compared to all the fluorescent proteins for single-molecule studies in vivo. This finding was subsequently used for demonstration of the applicability of eYFP in biophysical research. From tracking the lateral and rotational diffusion of eYFP in artificial material, and when bound to membranes of live cells, eYFP is found to dynamically track the entity to which it is anchored.
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Affiliation(s)
- G S Harms
- Department of Biophysics, Leiden University, Leiden, The Netherlands
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