301
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van den Brink-van der Laan E, Chupin V, Killian JA, de Kruijff B. Stability of KcsA Tetramer Depends on Membrane Lateral Pressure. Biochemistry 2004; 43:4240-50. [PMID: 15065868 DOI: 10.1021/bi036129d] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The potassium channel KcsA forms an extremely stable tetramer. Despite this high stability, it has been shown that the membrane-mimicking solvent 2,2,2-trifluoroethanol (TFE) can induce tetramer dissociation [Valiyaveetil, F. I., et al. (2002) Biochemistry 41, 10771-7, and Demmers, J. A. A., et al. (2003) FEBS Lett. 541, 69-77]. Here we have studied the effect of TFE on the structure and oligomeric state of the KcsA tetramer, reconstituted in different lipid systems. It was found that TFE changes the secondary and tertiary structure of KcsA and that it can dissociate the KcsA tetramer in all systems used. The tetramer is stabilized by a lipid bilayer as compared to detergent micelles. The extent of stabilization was found to depend on the nature of the lipids: a strong stabilizing effect of the nonbilayer lipid phosphatidylethanolamine (PE) was observed, but no effect of the charged phoshosphatidylglycerol (PG) as compared to phosphatidylcholine (PC) was found. To understand how lipids stabilize KcsA against TFE-induced tetramer dissociation, we also studied the effect of TFE on the bilayer organization in the various lipid systems, using (31)P and (2)H NMR. The observed lipid dependency was similar as was found for tetramer stabilization: PE increased the bilayer stability as compared to PC, while PG behaved similar to PC. Furthermore, it was found that TFE has a large effect on the acyl chain ordering. The results indicate that TFE inserts primarily in the membrane interface. We suggest that the lipid bilayer stabilizes the KcsA tetramer by the lateral pressure in the acyl chain region and that this stabilizing effect increases when a nonbilayer lipid like PE is present.
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Affiliation(s)
- Els van den Brink-van der Laan
- Department Biochemistry of Membranes, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands.
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302
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Sánchez ME, Turina ADV, García DA, Nolan MV, Perillo MA. Surface activity of thymol: implications for an eventual pharmacological activity. Colloids Surf B Biointerfaces 2004; 34:77-86. [PMID: 15261077 DOI: 10.1016/j.colsurfb.2003.11.007] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2003] [Revised: 09/24/2003] [Accepted: 11/23/2003] [Indexed: 11/18/2022]
Abstract
In the present work, we studied the ability of thymol to affect the organization of model membranes and the activity of an intrinsic membrane protein, the GABA(A) receptor (GABA(A)-R). In this last aspect, we tried to elucidate if the action mechanism of this terpene at the molecular level, involves its binding to the receptor protein, changes in the organization of the receptor molecular environment, or both. The self-aggregation of thymol in water with a critical micellar concentration approximately = 4 microM and its ability to penetrate in monomolecular layers of soybean phosphatidylcholine (sPC) at the air-water interface, even at surface pressures above the equilibrium, lateral pressure of natural bilayers were demonstrated. Thymol affected the self-aggregation of Triton X-100 and the topology of sPC vesicles. It also increased the polarity of the membrane environment sensed by the electrochromic dye merocyanine. A dipolar moment of 1.341 Debye was calculated from its energy-minimized structure. Its effect on the binding of [3H]-flunitrazepam ([3H]-FNZ) to chick brain synaptosomal membranes changed qualitatively from a tendency to the inhibition to a clear activatory regime, up on changing the phase state of the terpene (from a monomeric to a self-aggregated state). Above its CMC, thymol increased the affinity of the binding of [3H]-FNZ (K(d-control)= 2.9, K(d-thymol)= 1.7 nM) without changing the receptor density (B(max-control)= 910, B(max-thymol)= 895 fmol/mg protein). The activatory effect of thymol on the binding of [ [3H]-FNZ was observed even in the presence of the allosteric activator gamma-aminobutyric acid (GABA) at a concentration of maximal activity, and was blocked by the GABA antagonist bicuculline. Changes in the dipolar arrangement and in the molecular packing of GABA(A)-R environment are discussed as possible mediators of the action mechanism of thymol.
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Affiliation(s)
- Mariela E Sánchez
- Biofísica-Química, Departamento de Química, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Av. Vélez Sarsfield 1611, Córdoba 5016, Argentina
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303
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Hong H, Tamm LK. Elastic coupling of integral membrane protein stability to lipid bilayer forces. Proc Natl Acad Sci U S A 2004; 101:4065-70. [PMID: 14990786 PMCID: PMC384696 DOI: 10.1073/pnas.0400358101] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been traditionally difficult to measure the thermodynamic stability of membrane proteins because fully reversible protocols for complete folding these proteins were not available. Knowledge of the thermodynamic stability of membrane proteins is desirable not only from a fundamental theoretical standpoint, but is also of enormous practical interest for the rational design of membrane proteins and for optimizing conditions for their structure determination by crystallography or NMR. Here, we describe the design of a fully reversible system to study equilibrium folding of the outer membrane protein A from Escherichia coli in lipid bilayers. Folding is shown to be two-state under appropriate conditions permitting data analysis with a classical folding model developed for soluble proteins. The resulting free energy and m value, i.e., a measure of cooperativity, of unfolding are DeltaG(u,H2O)(o)=3.4 kcal/mol and m = 1.1 kcal/mol M(-1), respectively, in a reference bilayer composed of palmitoyl-oleoyl-phosphatidylcholine (C(16:0)C(18:1)PC) and palmitoyloleoyl-phosphatidylglycerol (C(16:0)C(18:1)PG). These values are strong functions of the lipid bilayer environment. By systematic variation of lipid headgroup and chain composition, we show that elastic bilayer forces such as curvature stress and hydrophobic mismatch modulate the free energy and cooperativity of folding of this and perhaps many other membrane proteins.
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Affiliation(s)
- Heedeok Hong
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, USA
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304
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de Vries AH, Mark AE, Marrink SJ. The Binary Mixing Behavior of Phospholipids in a Bilayer: A Molecular Dynamics Study. J Phys Chem B 2004. [DOI: 10.1021/jp0366926] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alex H. de Vries
- MD Group, Department of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Alan E. Mark
- MD Group, Department of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Siewert J. Marrink
- MD Group, Department of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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305
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Cantor RS. Receptor desensitization by neurotransmitters in membranes: are neurotransmitters the endogenous anesthetics? Biochemistry 2004; 42:11891-7. [PMID: 14556619 DOI: 10.1021/bi034534z] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A mechanism of anesthesia is proposed that addresses one of the most troubling peculiarities of general anesthesia: the remarkably small variability of sensitivity within the human population and across a broad range of animal phyla. It is hypothesized that in addition to the rapid, saturable binding of a neurotransmitter to its receptor that results in activation, the neurotransmitter also acts indirectly on the receptor by diffusing into the postsynaptic membrane and changing its physical properties, causing a shift in receptor conformational equilibrium (desensitization). Unlike binding, this slower indirect mechanism is nonspecific: each neurotransmitter will, in principle, affect all receptors in the membrane. For proteins modeled as having only resting and active conformational states, time-dependent ion currents are predicted that exhibit many characteristics of desensitization for both inhibitory and excitatory channels. If receptors have been engineered to regulate the time course of ion currents by this mechanism, then (a) mutations that significantly alter receptor sensitivity to this effect would be lethal and (b) by design, excitatory receptors would be inhibited, but inhibitory receptors activated, so that their effects are not counterproductive. The wide range of exogenous molecules that affect the physical properties of membranes as do neurotransmitters, but that do not bind to receptors, would thus inhibit excitatory channels and activate inhibitory channels, i.e., they would act as anesthesics. The endogenous anesthetics would thus be the neurotransmitters, the survival advantage conferred by their proper membrane-mediated desensitization of receptors explaining the selection pressure for anesthesic sensitivity.
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Affiliation(s)
- Robert S Cantor
- MEMPHYS-Center for Biomembrane Physics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
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306
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Falck E, Patra M, Karttunen M, Hyvönen MT, Vattulainen I. Impact of cholesterol on voids in phospholipid membranes. J Chem Phys 2004; 121:12676-89. [PMID: 15606294 DOI: 10.1063/1.1824033] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Free volume pockets or voids are important to many biological processes in cell membranes. Free volume fluctuations are a prerequisite for diffusion of lipids and other macromolecules in lipid bilayers. Permeation of small solutes across a membrane, as well as diffusion of solutes in the membrane interior are further examples of phenomena where voids and their properties play a central role. Cholesterol has been suggested to change the structure and function of membranes by altering their free volume properties. We study the effect of cholesterol on the properties of voids in dipalmitoylphosphatidylcholine (DPPC) bilayers by means of atomistic molecular dynamics simulations. We find that an increasing cholesterol concentration reduces the total amount of free volume in a bilayer. The effect of cholesterol on individual voids is most prominent in the region where the steroid ring structures of cholesterol molecules are located. Here a growing cholesterol content reduces the number of voids, completely removing voids of the size of a cholesterol molecule. The voids also become more elongated. The broad orientational distribution of voids observed in pure DPPC is, with a 30% molar concentration of cholesterol, replaced by a distribution where orientation along the bilayer normal is favored. Our results suggest that instead of being uniformly distributed to the whole bilayer, these effects are localized to the close vicinity of cholesterol molecules.
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Affiliation(s)
- Emma Falck
- Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, P.O. Box 1100, FI-02015 HUT, Finland.
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307
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Koubi L, Saiz L, Tarek M, Scharf D, Klein ML. Influence of Anesthetic and Nonimmobilizer Molecules on the Physical Properties of a Polyunsaturated Lipid Bilayer. J Phys Chem B 2003. [DOI: 10.1021/jp035169o] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Laure Koubi
- Center for Molecular Modeling and Chemistry Department, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, NIST Center for Neutron Research, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8562, Gaithersburg, Maryland 20899-8562, Equipe de Dynamique des Assemblages Membranaires, Unité Mixte de Recherche C.N.R.S./U.H.P. No. 7565, Universite Henri PoincaréNancy I, B.P. 239, F-54506 Vandoeuvre-lès
| | - Leonor Saiz
- Center for Molecular Modeling and Chemistry Department, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, NIST Center for Neutron Research, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8562, Gaithersburg, Maryland 20899-8562, Equipe de Dynamique des Assemblages Membranaires, Unité Mixte de Recherche C.N.R.S./U.H.P. No. 7565, Universite Henri PoincaréNancy I, B.P. 239, F-54506 Vandoeuvre-lès
| | - Mounir Tarek
- Center for Molecular Modeling and Chemistry Department, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, NIST Center for Neutron Research, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8562, Gaithersburg, Maryland 20899-8562, Equipe de Dynamique des Assemblages Membranaires, Unité Mixte de Recherche C.N.R.S./U.H.P. No. 7565, Universite Henri PoincaréNancy I, B.P. 239, F-54506 Vandoeuvre-lès
| | - Daphna Scharf
- Center for Molecular Modeling and Chemistry Department, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, NIST Center for Neutron Research, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8562, Gaithersburg, Maryland 20899-8562, Equipe de Dynamique des Assemblages Membranaires, Unité Mixte de Recherche C.N.R.S./U.H.P. No. 7565, Universite Henri PoincaréNancy I, B.P. 239, F-54506 Vandoeuvre-lès
| | - Michael L. Klein
- Center for Molecular Modeling and Chemistry Department, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, NIST Center for Neutron Research, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8562, Gaithersburg, Maryland 20899-8562, Equipe de Dynamique des Assemblages Membranaires, Unité Mixte de Recherche C.N.R.S./U.H.P. No. 7565, Universite Henri PoincaréNancy I, B.P. 239, F-54506 Vandoeuvre-lès
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308
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Rowat AC, Brask J, Sparrman T, Jensen KJ, Lindblom G, Ipsen JH. Farnesylated peptides in model membranes: a biophysical investigation. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2003; 33:300-9. [PMID: 14647993 DOI: 10.1007/s00249-003-0368-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2003] [Revised: 10/15/2003] [Accepted: 10/15/2003] [Indexed: 10/26/2022]
Abstract
Protein prenylation plays an important role in signal transduction, protein-protein interactions, and the localization and association of proteins with membranes. Using three different techniques, this study physically characterizes the interactions between model dimyristoylphosphatidylcholine membranes and a series of farnesylated peptides. Magic angle spinning nuclear Overhauser enhancement spectroscopy and differential scanning calorimetry reveal that both charged [Ac-Asn-Lys-Asn-Cys-(farnesyl)-OMe and Ac-Asn-Lys-Asn-Cys-(farnesyl)-NH(2)] and uncharged [Ac-Cys-(farnesyl)-OMe and farnesol] species partition into dimyristoylphosphatidylcholine bilayers. Calorimetry and vesicle fluctuation analysis of giant unilamellar vesicles show that the charged peptides modestly decrease the main gel-fluid phase transition and markedly increase the bending rigidity of large unilamellar vesicles. Uncharged species, on the other hand, dramatically decrease the main phase transition and modestly decrease the bending rigidity. No difference with carboxyl methylation is detected.
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Affiliation(s)
- Amy C Rowat
- MEMPHYS Centre for Biomembrane Physics, Department of Physics & Chemistry, University of Southern Denmark, Odense, Denmark
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309
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Affiliation(s)
- Pavel Strop
- California Institute of Technology, Pasadena, California 91125, USA
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310
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Zhang H, Kurisu G, Smith JL, Cramer WA. A defined protein-detergent-lipid complex for crystallization of integral membrane proteins: The cytochrome b6f complex of oxygenic photosynthesis. Proc Natl Acad Sci U S A 2003; 100:5160-3. [PMID: 12702760 PMCID: PMC154315 DOI: 10.1073/pnas.0931431100] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2002] [Accepted: 03/12/2003] [Indexed: 11/18/2022] Open
Abstract
The paucity of integral membrane protein structures creates a major bioinformatics gap, whose origin is the difficulty of crystallizing these detergent-solubilized proteins. The problem is particularly formidable for hetero-oligomeric integral membrane proteins, where crystallization is impeded by the heterogeneity and instability of the protein subunits and the small lateral pressure imposed by the detergent micelle envelope that surrounds the hydrophobic domain. In studies of the hetero (eight subunit)-dimeric 220,000 molecular weight cytochrome b(6)f complex, derived from the thermophilic cyanobacterium, Mastigocladus laminosus, crystals of the complex in an intact state could not be obtained from highly purified delipidated complex despite exhaustive screening. Crystals of proteolyzed complex could be obtained that grew very slowly and diffracted poorly. Addition to the purified lipid-depleted complex of a small amount of synthetic nonnative lipid, dioleolyl-phosphatidylcholine, resulted in a dramatic improvement in crystallization efficiency. Large crystals of the intact complex grew overnight, whose diffraction parameters are as follows: 94% complete at 3.40 A spacing; R(merge) = 8.8% (38.5%), space group, P6(1)22; and unit cell parameters, a = b = 156.3 A, c = 364.0 A, alpha = beta = 90 degrees, gamma = 120 degrees. It is proposed that the methodology of augmentation of a well-defined lipid-depleted integral membrane protein complex with synthetic nonnative lipid, which can provide conformational stability to the protein complex, may be of general use in the crystallization of integral membrane proteins.
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Affiliation(s)
- Huamin Zhang
- Department of Biological Sciences, Lilly Hall of Life Sciences, Purdue University, West Lafayette, IN 47907-2054, USA
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311
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Abstract
Early experiments and molecular simulations of PUFA favored a rigid arrangement of double bonds in U-shaped or extended conformations such as angle-iron or helical. Although results of recent solid-state NMR measurements and molecular simulations have confirmed the existence of these structural motifs, they portray an image of DHA (22:6n-3) as a highly flexible molecule with rapid transitions between large numbers of conformers on the time scale from picoseconds to hundreds of nanoseconds. The low barriers to torsional rotation about C-C bonds that link the cis-locked double bonds with the methylene carbons between them are responsible for this unusual flexibility. Both the amplitude and frequency of motion increase toward the terminal methyl group of DHA.
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Affiliation(s)
- Klaus Gawrisch
- Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Rockville, Maryland 20852, USA.
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312
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Leermakers FAM, Rabinovich AL, Balabaev NK. Self-consistent-field modeling of hydrated unsaturated lipid bilayers in the liquid-crystal phase and comparison to molecular dynamics simulations. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 67:011910. [PMID: 12636535 DOI: 10.1103/physreve.67.011910] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2001] [Indexed: 05/24/2023]
Abstract
A molecular-level self-consistent-field (SCF) theory is applied to model the lipid bilayer structures composed of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (18:0/18:1 omega 9cis PC) and 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphatidylcholine (18:0/22:6 omega 3cis PC). As compared to earlier attempts to model (saturated) PC membranes several additional features are implemented: (i) A water model is used which correctly leads to low water concentration in the bilayers. (ii) Free volume is allowed for, which is important to obtain bilayers in the fluid state. (iii) A polarization term is included in the segment potentials; this new feature corrects for a minor thermodynamic inconsistency present in (all) earlier results for charged bilayers. (iv) The CH3 groups in the lipid molecules are assumed to have twice the volume of a CH2 group; this leads to stable noninterdigitated bilayers. (v) A cis double bond is simulated by forcing gauche conformations along the sn-2 acyl chain. Results of an all-atom molecular dynamics (MD) simulation, using the collision dynamics method, on the same system are presented. Both SCF and MD prove, in accordance with experimental facts, that acyl unsaturation effectively reduces the length of the chain which counteracts interdigitation. It is also found that the phosphatidylcholine head group is lying almost flat on the membrane surface and the water penetrates into the bilayer upto the glycerol backbone units. From the SCF results it further followed that the free volume is not exactly evenly distributed over the bilayer. There is a small increase in free volume in the center of the bilayer as well as in the glycerol backbone region.
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Affiliation(s)
- F A M Leermakers
- Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands
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313
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Shillcock JC, Lipowsky R. Equilibrium structure and lateral stress distribution of amphiphilic bilayers from dissipative particle dynamics simulations. J Chem Phys 2002. [DOI: 10.1063/1.1498463] [Citation(s) in RCA: 306] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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314
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Pratt LR, Pohorille A. Hydrophobic effects and modeling of biophysical aqueous solution interfaces. Chem Rev 2002; 102:2671-92. [PMID: 12175264 DOI: 10.1021/cr000692+] [Citation(s) in RCA: 329] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Lawrence R Pratt
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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315
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Dean DM, Nguitragool W, Miri A, McCabe SL, Zimmerman AL. All-trans-retinal shuts down rod cyclic nucleotide-gated ion channels: a novel role for photoreceptor retinoids in the response to bright light? Proc Natl Acad Sci U S A 2002; 99:8372-7. [PMID: 12034887 PMCID: PMC123074 DOI: 10.1073/pnas.122681899] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2001] [Indexed: 11/18/2022] Open
Abstract
In retinal rods, light-induced isomerization of 11-cis-retinal to all-trans-retinal within rhodopsin triggers an enzyme cascade that lowers the concentration of cGMP. Consequently, cyclic nucleotide-gated (CNG) ion channels close, generating the first electrical response to light. After isomerization, all-trans-retinal dissociates from rhodopsin. We now show that all-trans-retinal directly and markedly inhibits cloned rod CNG channels in excised patches. 11-cis-retinal and all-trans-retinol also inhibited the channels, but at somewhat higher concentrations. Single-channel analysis suggests that all-trans-retinal reduces average open probability of rod CNG channels by inactivating channels for seconds at a time. At physiological cGMP levels, all-trans-retinal inhibited in the nanomolar range. Our results suggest that all-trans-retinal may be a potent regulator of the channel in rods during the response to bright light, when there is a large surge in the concentration of all-trans-retinal.
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Affiliation(s)
- Dylan M Dean
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, RI 02912, USA
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316
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Botelho AV, Gibson NJ, Thurmond RL, Wang Y, Brown MF. Conformational energetics of rhodopsin modulated by nonlamellar-forming lipids. Biochemistry 2002; 41:6354-68. [PMID: 12009897 DOI: 10.1021/bi011995g] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rhodopsin is an important example of a G protein-coupled receptor (GPCR) in which 11-cis-retinal is the ligand and acts as an inverse agonist. Photolysis of rhodopsin leads to formation of the activated meta II state from its precursor meta I. Various mechanisms have been proposed to explain how the membrane composition affects the meta I-meta II conformational equilibrium in the visual process. For rod disk membranes and recombinant membranes containing rhodopsin, the lipid properties have been discussed in terms of elastic deformation of the bilayer. Here we have investigated the relation of nonlamellar-forming lipids, such as dioleoylphosphatidylethanolamine (DOPE), together with dioleoylphosphatidylcholine (DOPC), to the photochemistry of membrane-bound rhodopsin. We conducted flash photolysis experiments for bovine rhodopsin recombined with DOPE/DOPC mixtures (0:100 to 75:25) as a function of pH to explore the dependence of the photochemical activity on the monolayer curvature free energy of the membrane. It is well-known that DOPC forms bilayers, whereas DOPE has a propensity to adopt the nonlamellar, reverse hexagonal (H(II)) phase. In the case of neutral DOPE/DOPC recombinants, calculations of the membrane surface pH confirmed that an increase in DOPE favored the meta II state. Moreover, doubling the PE headgroup content versus the native rod membranes substituted for the polyunsaturated, docosahexaenoic acyl chains (22:6 omega 3), suggesting rhodopsin function is associated with a balance of forces within the bilayer. The data are interpreted by applying a flexible surface model, in which the meta II state is stabilized by lipids tending to form the H(II) phase, with a negative spontaneous curvature. A simple theory, based on principles of surface chemistry, for coupling the energetics of membrane proteins to material properties of the bilayer lipids is described. For rhodopsin, the free energy balance of the receptor and the lipids is altered by photoisomerization of retinal and involves curvature stress/strain of the membrane (frustration). A new biophysical principle is introduced: matching of the spontaneous curvature of the lipid bilayer to the mean curvature of the lipid/water interface adjacent to the protein, which balances the lipid/protein solvation energy. In this manner, the thermodynamic driving force for the meta I-meta II conformational change of rhodopsin is tightly controlled by mixtures of nonlamellar-forming lipids having distinctive material properties.
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Affiliation(s)
- Ana Vitória Botelho
- Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721, USA
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317
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Cantor RS. Size distribution of barrel-stave aggregates of membrane peptides: influence of the bilayer lateral pressure profile. Biophys J 2002; 82:2520-5. [PMID: 11964240 PMCID: PMC1302042 DOI: 10.1016/s0006-3495(02)75595-1] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Some membrane peptides, such as Alamethicin, form barrel-stave aggregates with a broad probability distribution of size (number of peptides in the aggregate). This distribution has been shown to depend on the characteristics of the lipid bilayer. A mechanism for this influence is suggested, in analogy to earlier work on the effects of changes in bilayer composition on conformational equilibria in membrane proteins, that is based on coupling of shifts in the distribution of lateral pressures in the bilayer to depth-dependent changes in the lateral excluded area that accompanies the formation of an aggregate. Thermodynamic analysis is coupled with a simple geometric model of aggregates of kinked cylindrical peptides and with results of previously calculated lateral pressure distributions to predict the effects of changes in bilayer characteristics on aggregate size distributions, in qualitative agreement with experimental results.
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Affiliation(s)
- Robert S Cantor
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA.
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318
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Poolman B, Blount P, Folgering JHA, Friesen RHE, Moe PC, van der Heide T. How do membrane proteins sense water stress? Mol Microbiol 2002; 44:889-902. [PMID: 12010487 DOI: 10.1046/j.1365-2958.2002.02894.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Maintenance of cell turgor is a prerequisite for almost any form of life as it provides a mechanical force for the expansion of the cell envelope. As changes in extracellular osmolality will have similar physicochemical effects on cells from all biological kingdoms, the responses to osmotic stress may be alike in all organisms. The primary response of bacteria to osmotic upshifts involves the activation of transporters, to effect the rapid accumulation of osmoprotectants, and sensor kinases, to increase the transport and/or biosynthetic capacity for these solutes. Upon osmotic downshift, the excess of cytoplasmic solutes is released via mechanosensitive channel proteins. A number of breakthroughs in the last one or two years have led to tremendous advances in our understanding of the molecular mechanisms of osmosensing in bacteria. The possible mechanisms of osmosensing, and the actual evidence for a particular mechanism, are presented for well studied, osmoregulated transport systems, sensor kinases and mechanosensitive channel proteins. The emerging picture is that intracellular ionic solutes (or ionic strength) serve as a signal for the activation of the upshift-activated transporters and sensor kinases. For at least one system, there is strong evidence that the signal is transduced to the protein complex via alterations in the protein-lipid interactions rather than direct sensing of ion concentration or ionic strength by the proteins. The osmotic downshift-activated mechanosensitive channels, on the other hand, sense tension in the membrane but other factors such as hydration state of the protein may affect the equilibrium between open and closed states of the proteins.
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Affiliation(s)
- Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh, Groningen, The Netherlands.
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319
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Dopico AM, Walsh JV, Singer JJ. Natural bile acids and synthetic analogues modulate large conductance Ca2+-activated K+ (BKCa) channel activity in smooth muscle cells. J Gen Physiol 2002; 119:251-73. [PMID: 11865021 PMCID: PMC2217287 DOI: 10.1085/jgp.20028537] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2002] [Revised: 01/28/2002] [Accepted: 01/28/2002] [Indexed: 01/29/2023] Open
Abstract
Bile acids have been reported to produce relaxation of smooth muscle both in vitro and in vivo. The cellular mechanisms underlying bile acid-induced relaxation are largely unknown. Here we demonstrate, using patch-clamp techniques, that natural bile acids and synthetic analogues reversibly increase BK(Ca) channel activity in rabbit mesenteric artery smooth muscle cells. In excised inside-out patches bile acid-induced increases in channel activity are characterized by a parallel leftward shift in the activity-voltage relationship. This increase in BK(Ca) channel activity is not due to Ca(2+)-dependent mechanism(s) or changes in freely diffusible messengers, but to a direct action of the bile acid on the channel protein itself or some closely associated component in the cell membrane. For naturally occurring bile acids, the magnitude of bile acid-induced increase in BK(Ca) channel activity is inversely related to the number of hydroxyl groups in the bile acid molecule. By using synthetic analogues, we demonstrate that such increase in activity is not affected by several chemical modifications in the lateral chain of the molecule, but is markedly favored by polar groups in the side of the steroid rings opposite to the side where the methyl groups are located, which stresses the importance of the planar polarity of the molecule. Bile acid-induced increases in BK(Ca) channel activity are also observed in smooth muscle cells freshly dissociated from rabbit main pulmonary artery and gallbladder, raising the possibility that a direct activation of BK(Ca) channels by these planar steroids is a widespread phenomenon in many smooth muscle cell types. Bile acid concentrations that increase BK(Ca) channel activity in mesenteric artery smooth muscle cells are found in the systemic circulation under a variety of human pathophysiological conditions, and their ability to enhance BK(Ca) channel activity may explain their relaxing effect on smooth muscle.
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Affiliation(s)
- Alejandro M Dopico
- Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, 874 Union Avenue, Memphis, TN 39163, USA.
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320
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Huber T, Rajamoorthi K, Kurze VF, Beyer K, Brown MF. Structure of docosahexaenoic acid-containing phospholipid bilayers as studied by (2)H NMR and molecular dynamics simulations. J Am Chem Soc 2002; 124:298-309. [PMID: 11782182 DOI: 10.1021/ja011383j] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Polyunsaturated phospholipids are known to be important with regard to the biological functions of essential fatty acids, for example, involving neural tissues such as the brain and retina. Here we have employed two complementary structural methods for the study of polyunsaturated bilayer lipids, viz. deuterium ((2)H) NMR spectroscopy and molecular dynamics (MD) computer simulations. Our research constitutes one of the first applications of all-atom MD simulations to polyunsaturated lipids containing docosahexaenoic acid (DHA; 22:6 cis-Delta(4,7,10,13,16,19)). Structural features of the highly unsaturated, mixed-chain phospholipid, 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (PDPC), have been studied in the liquid-crystalline (L(alpha)) state and compared to the less unsaturated homolog, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The (2)H NMR spectra of polyunsaturated bilayers are dramatically different from those of less unsaturated phospholipid bilayers. We show how use of MD simulations can aid in interpreting the complex (2)H NMR spectra of polyunsaturated bilayers, in conjunction with electron density profiles determined from small-angle X-ray diffraction studies. This work clearly demonstrates preferred helical and angle-iron conformations of the polyunsaturated chains in liquid-crystalline bilayers, which favor chain extension while maintaining bilayer flexibility. The presence of relatively long, extended fatty acyl chains may be important for solvating the hydrophobic surfaces of integral membrane proteins, such as rhodopsin. In addition, the polyallylic DHA chains have a tendency to adopt back-bended (hairpin-like) structures, which increase the interfacial area per lipid. Finally, the material properties have been analyzed in terms of the response of the bilayer to mechanical stress. Simulated bilayers of phospholipids containing docosahexaenoic acid were less sensitive to the applied surface tension than were saturated phospholipids, possibly implying a decrease in membrane elasticity (area elastic modulus, bending rigidity). The above features distinguish DHA-containing lipids from saturated or monounsaturated lipids and may be important for their biological modes of action.
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Affiliation(s)
- Thomas Huber
- Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA
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321
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A monolayer study of properties of isolated membrane phospholipids of ‘Bacillus subtilis’. Colloids Surf B Biointerfaces 2002. [DOI: 10.1016/s0927-7765(01)00202-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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322
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Weiss HM, Grisshammer R. Purification and characterization of the human adenosine A(2a) receptor functionally expressed in Escherichia coli. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:82-92. [PMID: 11784301 DOI: 10.1046/j.0014-2956.2002.02618.x] [Citation(s) in RCA: 169] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The adenosine A(2a) receptor belongs to the seven transmembrane helix G-protein-coupled receptor family, is abundant in striatum, vasculature and platelets and is involved in several physiological processes such as blood pressure regulation and protection of cells during anoxia. For structural and biophysical studies we have expressed the human adenosine A(2a) receptor (hA2aR) at high levels inserted into the Escherichia coli inner membrane, and established a purification scheme. Expression was in fusion with the periplasmic maltose-binding protein to levels of 10-20 nmol of receptor per L of culture, as detected with the specific antagonist ligand [(3)H]ZM241385. As the receptor C-terminus was proteolyzed upon solubilization, a protease-resistant but still functional receptor was created by truncation to Ala316. Addition of the sterol, cholesteryl hemisuccinate, allowed a stable preparation of functional hA2aR solubilized in dodecylmaltoside to be obtained, and, increased the stability of the receptor solubilized in other alkylmaltosides. Purification to homogeneity was achieved in three steps, including ligand affinity chromatography based on the antagonist xanthine amine congener. The purified hA2aR fusion protein bound [(3)H]ZM241385 with a K(d) of 0.19 nm and an average B(max) of 13.7 nmol x mg(-1) that suggests 100% functionality. Agonist affinities for the purified solubilized receptor were higher than those for the membrane-bound form. Sufficient pure, functional hA2aR can now be prepared regularly for structural studies.
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Affiliation(s)
- H Markus Weiss
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge, UK.
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323
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McIntosh TJ, Vidal A, Simon SA. The energetics of peptide-lipid interactions: Modulation by interfacial dipoles and cholesterol. PEPTIDE-LIPID INTERACTIONS 2002. [DOI: 10.1016/s1063-5823(02)52013-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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324
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van der Heide T, Stuart MC, Poolman B. On the osmotic signal and osmosensing mechanism of an ABC transport system for glycine betaine. EMBO J 2001; 20:7022-32. [PMID: 11742979 PMCID: PMC125795 DOI: 10.1093/emboj/20.24.7022] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The osmosensing mechanism of the ATP-binding cassette (ABC) transporter OpuA of Lactococcus lactis has been elucidated for the protein reconstituted in liposomes. Activation of OpuA by osmotic upshift was instantaneous and reversible and followed changes in volume and membrane structure of the proteoliposomes. Osmotic activation of OpuA was dependent on the fraction of anionic lipids present in the lipid bilayer. Also, cationic and anionic lipophilic amphiphiles shifted the activation profile in a manner indicative of an osmosensing mechanism, in which electrostatic interactions between lipid headgroups and the OpuA protein play a major role. Further support for this notion came from experiments in which ATP-driven uptake and substrate-dependent ATP hydrolysis were measured with varying concentrations of osmolytes at the cytoplasmic face of the protein. Under iso-osmotic conditions, the transporter could be activated by high concentrations of ionic osmolytes, whereas neutral ones had no effect, demonstrating that intracellular ionic strength, rather than a specific signaling molecule or water activity, signals osmotic stress to the transporter. The data indicate that OpuA is under the control of a mechanism in which the membrane and ionic strength act in concert to signal osmotic changes.
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Affiliation(s)
- Tiemen van der Heide
- Departments of
Biochemistry and Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands Corresponding author e-mail:
| | - Marc C.A. Stuart
- Departments of
Biochemistry and Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands Corresponding author e-mail:
| | - Bert Poolman
- Departments of
Biochemistry and Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands Corresponding author e-mail:
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325
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Binder H, Gawrisch K. Effect of Unsaturated Lipid Chains on Dimensions, Molecular Order and Hydration of Membranes. J Phys Chem B 2001. [DOI: 10.1021/jp010118h] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hans Binder
- University of Leipzig, Institute of Medical Physics and Biophysics, Liebigstr. 27, D-04103 Leipzig, Germany, and NIH, NIAAA, Laboratory of Membrane Biochemistry and Biophysics, 12420 Parklawn Drive, Rockville, Maryland 20852
| | - Klaus Gawrisch
- University of Leipzig, Institute of Medical Physics and Biophysics, Liebigstr. 27, D-04103 Leipzig, Germany, and NIH, NIAAA, Laboratory of Membrane Biochemistry and Biophysics, 12420 Parklawn Drive, Rockville, Maryland 20852
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326
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Rosenbusch JP. Stability of membrane proteins: relevance for the selection of appropriate methods for high-resolution structure determinations. J Struct Biol 2001; 136:144-57. [PMID: 11886216 DOI: 10.1006/jsbi.2001.4431] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
High stability is a prominent characteristic of integral membrane proteins of known atomic structure. But rather than being an intrinsic property, it may be due to a selection exerted by biochemical procedures prior to structure determination, since solubilization results in the transient exposure of membrane proteins to solution conditions. This may cause structural perturbations that interfere with 3D crystallization and hence with X-ray analysis. This problem also affects the preparation of samples for electron crystallography and NMR studies and may account for the fact that high-resolution structures of representatives of whole groups, such as transport proteins and signal transducers, have not been elucidated so far by any method. A knowledge of the proportion of labile proteins among membrane proteins, and of the kinetics of their denaturation, is therefore necessary. Establishing stability profiles, developing methods to maintain lateral pressure, or preventing contact with water (or both) should prove significant in establishing the structures of conformationally flexible proteins.
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327
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Rübenhagen R, Morbach S, Krämer R. The osmoreactive betaine carrier BetP from Corynebacterium glutamicum is a sensor for cytoplasmic K+. EMBO J 2001; 20:5412-20. [PMID: 11574473 PMCID: PMC125657 DOI: 10.1093/emboj/20.19.5412] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The isolated glycine betaine uptake carrier BetP from Corynebacterium glutamicum was reconstituted in Escherichia coli phospholipid liposomes and its response to osmotic stress studied. The transport activity of BetP, which was previously shown to comprise both osmosensory and osmoregulatory functions, was used to identify the nature of the physicochemical stimulus related to hyperosmotic stress. Putative factors modulating transport activity in response to osmotic stress were dissected. These include type, osmolality and concentration of solutes in the internal and/or external compartment (cationic, anionic, zwitterionic, neutral), as well as membrane strain as a response to increased osmolality. Osmoresponsive activation of BetP was independent of any external factor and of physical alterations of the membrane, but was triggered by a change in the internal K+ concentration. Activation did not depend on the type of anion present and was K+ (or Cs+ and Rb+) specific, as choline and NH(4)+ did not trigger BetP activity. The half-maximal activation of BetP in E.coli phospholipid liposomes was correlated to an internal concentration of 221 +/- 23 mM K+.
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Affiliation(s)
| | | | - Reinhard Krämer
- Institut für Biochemie, Universität zu Köln, D-50674 Köln, Germany
Corresponding author e-mail:
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328
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Abstract
The surface expansion that is induced by the lateral pressure in the brush region of lipid membranes containing grafted polymers is deduced from the scaling and mean-field theories for the polymer brush, together with the equation of state for a lipid monolayer at the equivalence pressure with fluid lipid bilayers. Depending on the length and mole fraction of the polymer lipid, the membrane expansion can be appreciable. Direct experimental evidence for this lateral expansion comes from recent spin-label measurements with lipid membranes containing poly(ethylene glycol)-grafted lipids. The expansion in lipid area modifies the elastic constants of the polymer-grafted membranes in a way that opposes the direct elastic response of the polymer itself. Calculations as a function of polymer lipid content indicate that the net change in isothermal area expansion modulus of the membrane is negative but small, in contrast to previous predictions. A similar situation applies to the curvature elastic moduli of membranes containing short polymer lipids. For longer polymer lipids, however, the direct contribution of the polymer brush to the bending elastic constants dominates, and the increase in bending moduli with increasing polymer lipid content rapidly exceeds the basal values of the bare lipid membrane. The spontaneous (or intrinsic) curvature of the component monolayer of polymer lipid-containing membranes is calculated for the first time. The polymer brush contribution to spontaneous curvature scales quadratically with the polymer length, and at least quadratically with the mole fraction of polymer lipid.
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Affiliation(s)
- D Marsh
- Abt. Spektroskopie, Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany.
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329
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Saiz L, Klein ML. Influence of highly polyunsaturated lipid acyl chains of biomembranes on the NMR order parameters. J Am Chem Soc 2001; 123:7381-7. [PMID: 11472169 DOI: 10.1021/ja003987d] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
We investigate the effect of specific conformations of double-bond segments in highly polyunsaturated acyl chains on the deuterium (2)H NMR order parameters of a fully hydrated 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (SDPC, 18:0/22:6 PC) lipid bilayer. The system is analyzed by performing a molecular dynamics simulation study at ambient conditions in the fluid lamellar phase. By separately calculating the different partial contributions to the total order parameter profiles measurable experimentally, we are able to get insights into the molecular origin of earlier experimental and theoretical observations. The effect of the position of the different conformations of double-bond segments along the polyunsaturated acyl chain is also examined. As in experiments performed in a series of lipid bilayers with an increasing number of cis double bonds per lipid molecule [Holte, L. L., et al. Biophys. J. 1995, 68, 2396], we find that unsaturations influence mainly the order of the bottom half of the saturated chain. Specific conformations of the polyunsaturated chain close to the lipid headgroups have a distinct effect on the order of the bottom half of the saturated chain and on the top half of the polyunsaturated chain. Our results indicate that for SDPC the conformation of the region of the polyunsaturated chain located between the first three cis double bonds is responsible for the major effects on the orientational order of both the saturated and the polyunsaturated chains.
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Affiliation(s)
- L Saiz
- Contribution from the Center for Molecular Modeling and Chemistry Department, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA.
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330
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Cantor RS. Bilayer Partition Coefficients of Alkanols: Predicted Effects of Varying Lipid Composition. J Phys Chem B 2001. [DOI: 10.1021/jp010244l] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Robert S. Cantor
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755
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331
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Saiz L, Klein ML. Structural properties of a highly polyunsaturated lipid bilayer from molecular dynamics simulations. Biophys J 2001; 81:204-16. [PMID: 11423407 PMCID: PMC1301504 DOI: 10.1016/s0006-3495(01)75692-5] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The structure of a fully hydrated mixed (saturated/polyunsaturated) chain lipid bilayer in the biologically relevant liquid crystalline phase has been examined by performing a molecular dynamics study. The model membrane, a 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (SDPC, 18:0/22:6 PC) lipid bilayer, was investigated at constant (room) temperature and (ambient) pressure, and the results obtained in the nanosecond time scale reproduced quite well the available experimental data. Polyunsaturated fatty acids are found in high concentrations in neuronal and retinal tissues and are essential for the development of human brain function. The docosahexaenoic fatty acid, in particular, is fundamental for the proper function of the visual receptor rhodopsin. The lipid bilayer order has been investigated through the orientational order parameters. The water-lipid interface has been explored thoroughly in terms of its dimensions and the organization of the different components. Several types of interactions occurring in the system have been analyzed, specifically, the water-hydrocarbon chain, lipid-lipid and lipid-water interactions. The distribution of dihedral angles along the chains and the molecular conformations of the polyunsaturated chain of the lipids have also been studied. Special attention has been focused on the microscopic (molecular) origin of the effects of polyunsaturations on the different physical properties of membranes.
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Affiliation(s)
- L Saiz
- Center for Molecular Modeling, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
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332
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Cantor RS. Breaking the Meyer-Overton rule: predicted effects of varying stiffness and interfacial activity on the intrinsic potency of anesthetics. Biophys J 2001; 80:2284-97. [PMID: 11325730 PMCID: PMC1301419 DOI: 10.1016/s0006-3495(01)76200-5] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Exceptions to the Meyer-Overton rule are commonly cited as evidence against indirect, membrane-mediated mechanisms of general anesthesia. However, another interpretation is possible within the context of an indirect mechanism in which solubilization of an anesthetic in the membrane causes a redistribution of lateral pressures in the membrane, which in turn shifts the conformational equilibrium of membrane proteins such as ligand-gated ion channels. It is suggested that compounds of different stiffness and interfacial activity have different intrinsic potencies, i.e., they cause widely different redistributions of the pressure profile (and thus different effects on protein conformational equilibria) per unit concentration of the compound in the membrane. Calculations incorporating the greater stiffness of perfluoromethylenic chains and the large interfacial attraction of hydroxyl groups predict the higher intrinsic potency of short alkanols than alkanes, the cutoffs in potency of alkanes and alkanols and the much shorter cutoffs for their perfluorinated analogues. Both effects, increased stiffness and interfacial activity, are present in unsaturated hydrocarbon solutes, and the intrinsic potencies are predicted to depend on the magnitude of both effects and on the number and locations of multiple bonds within the molecule. Most importantly, the intrinsic potencies of polymeric alkanols with regularly spaced hydroxyl groups are predicted to rise with increasing chain length, without cutoff; such molecules should serve to distinguish unambiguously between indirect mechanisms and direct binding mechanisms of anesthesia.
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Affiliation(s)
- R S Cantor
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA.
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333
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Lahajnar G, Macek P, Zupancic I. Suppression of red cell diffusional water permeability by lipophilic solutes. Bioelectrochemistry 2000; 52:179-85. [PMID: 11129241 DOI: 10.1016/s0302-4598(00)00100-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The inhibitory effect of a series of neutral lipophilic solutes (methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-amylalcohol, n-hexanol, diethylether, nitrobenzene, and pyridine) on the diffusional water permeability (Pd, tot) of bovine erythrocyte membrane at 25 degrees C was studied in comparison to that of p-chloromercuri benzoate (pCMB). Permeability data were obtained by measuring the transmembrane diffusional water exchange time tau(exch) using an 1H-T2 NMR technique. Maximal inhibition by approximately 50% of Pd, tot was produced by 2 mM pCMB which completely blocked the membrane water channels in 20 min, hence suggesting the channel-to-lipid diffusional water permeability ratio of about 1:1. Furthermore, the maximal inhibitory effect of pCMB in combination with the lipophilic solutes was lower than that of pCMB alone. As pCMB does not interfere with the lipid bilayer, and provided that it blocks the water channels in solute presence as well, this confirms that the solutes induce an increase in the lipid-mediated background water permeability contribution (Pd, lipid) by the formation of aqueous leaks in the membrane hydrophobic barrier. However, faster but less efficient in permeability inhibition than pCMB (either alone or combined with solutes) were the lipophilic solutes alone. Taken together, the results indicate that the lipophilic solutes suppress the membrane total permeability Pd, tot by two opposing effects: a reduction of its channel-mediated part (Pd, channel) to the extent exceeding that of a simultaneous Pd, lipid increase. The inhibitory potency of the solutes tested appears to be correlated with their solubility in the membrane medium.
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Affiliation(s)
- G Lahajnar
- Jozef Stefan Institute, Ljubljana, Slovenia.
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334
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Crary JI, Dean DM, Nguitragool W, Kurshan PT, Zimmerman AL. Mechanism of inhibition of cyclic nucleotide-gated ion channels by diacylglycerol. J Gen Physiol 2000; 116:755-68. [PMID: 11099345 PMCID: PMC2231817 DOI: 10.1085/jgp.116.6.755] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) channels are critical components in the visual and olfactory signal transduction pathways, and they primarily gate in response to changes in the cytoplasmic concentration of cyclic nucleotides. We previously found that the ability of the native rod CNG channel to be opened by cGMP was markedly inhibited by analogues of diacylglycerol (DAG) without a phosphorylation reaction (Gordon, S.E., J. Downing-Park, B. Tam, and A.L. Zimmerman. 1995. Biophys. J. 69:409-417). Here, we have studied cloned bovine rod and rat olfactory CNG channels expressed in Xenopus oocytes, and have determined that they are differentially inhibited by DAG. At saturating [cGMP], DAG inhibition of homomultimeric (alpha subunit only) rod channels was similar to that of the native rod CNG channel, but DAG was much less effective at inhibiting the homomultimeric olfactory channel, producing only partial inhibition even at high [DAG]. However, at low open probability (P(o)), both channels were more sensitive to DAG, suggesting that DAG is a closed state inhibitor. The Hill coefficients for DAG inhibition were often greater than one, suggesting that more than one DAG molecule is required for effective inhibition of a channel. In single-channel recordings, DAG decreased the P(o) but not the single-channel conductance. Results with chimeras of rod and olfactory channels suggest that the differences in DAG inhibition correlate more with differences in the transmembrane segments and their attached loops than with differences in the amino and carboxyl termini. Our results are consistent with a model in which multiple DAG molecules stabilize the closed state(s) of a CNG channel by binding directly to the channel and/or by altering bilayer-channel interactions. We speculate that if DAG interacts directly with the channel, it may insert into a putative hydrophobic crevice among the transmembrane domains of each subunit or at the hydrophobic interface between the channel and the bilayer.
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Affiliation(s)
- Jennifer I. Crary
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island 02912
| | - Dylan M. Dean
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island 02912
| | - Wang Nguitragool
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island 02912
| | - Peri T. Kurshan
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island 02912
| | - Anita L. Zimmerman
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island 02912
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335
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Nielsen C, Andersen OS. Inclusion-induced bilayer deformations: effects of monolayer equilibrium curvature. Biophys J 2000; 79:2583-604. [PMID: 11053132 PMCID: PMC1301140 DOI: 10.1016/s0006-3495(00)76498-8] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The energetics of protein-induced bilayer deformation in systems with finite monolayer equilibrium curvature were investigated using an elastic membrane model. In this model the bilayer deformation energy delta G(def) has two major components: a compression-expansion component and a splay-distortion component, which includes the consequences of a bilayer curvature frustration due to a monolayer equilibrium curvature, c(0), that is different from zero. For any choice of bilayer material constants, the value of delta G(def) depends on global bilayer properties, as described by the bilayer material constants, as well as the energetics of local lipid packing adjacent to the protein. We introduce this dependence on lipid packing through the contact slope, s, at the protein-bilayer boundary. When c(0) = 0, delta G(def) can be approximated as a biquadratic function of s and the monolayer deformation at the protein/bilayer boundary, u(0): delta G(def) = a(1)u(0)(2) + a(2)u(0)s + a(3)s(2), where a(1), a(2), and a(3) are functions of the bilayer thickness, the bilayer compression-expansion and splay-distortion moduli, and the inclusion radius (this expression becomes exact when the Gaussian curvature component of delta G(def) is negligible). When c(0) not equal 0, the curvature frustration contribution is determined by the choice of boundary conditions at the protein-lipid boundary (by the value of s), and delta G(def) is the sum of the energy for c(0) = 0 plus the curvature frustration-dependent contribution. When the energetic penalty for the local lipid packing can be ignored, delta G(def) will be determined only by the global bilayer properties, and a c(0) > 0 will tend to promote a local inclusion-induced bilayer thinning. When the energetic penalty for local lipid packing is large, s will be constrained by the value of c(0). In a limiting case, where s is determined only by geometric constraints imposed by c(0), a c(0) > 0 will impede such local bilayer thinning. One cannot predict curvature effects without addressing the proper choice of boundary conditions at the protein-bilayer contact surface.
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Affiliation(s)
- C Nielsen
- Department of Physiology and Biophysics, Cornell University, Weill Medical College, New York, New York 10021, USA.
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336
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Noula C, Bonzom P, Brown A, Gibbons WA, Martin J, Nicolaou A. 1H-NMR lipid profiles of human blood platelets; links with coronary artery disease. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1487:15-23. [PMID: 11004608 DOI: 10.1016/s1388-1981(00)00078-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Blood platelets are closely involved in the early development of atherosclerosis and in the events that lead to thrombosis, both of which are dominating factors in coronary artery disease (CAD). The aim of the present study was to evaluate the platelet lipid profiles of patients suffering from CAD and explore the possibility of a link between platelet lipids and CAD, using high-resolution high-field proton nuclear magnetic resonance spectroscopy as the analytical tool. The total platelet lipid profiles of healthy volunteers were compared with those of patients presenting with chest pain requiring coronary angiography. Two lipid groups changed significantly: cholesterol increased by 16.5% and total diacylglycerophospholipids decreased by 15.7%. There was also a significant decrease of the ethanolamine-containing phospholipids, by 4.7%; the extent of unsaturation of the fatty acid chains, by 0.2, and increase of the linoleate content of the fatty acid chains, by 1.9%. Our results suggest that platelet lipid abnormalities occur in patients with CAD and these changes may predate the development of overt atherosclerosis.
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Affiliation(s)
- C Noula
- University-Industry Centre for Pharmaceutical Research, School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, UK
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337
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338
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339
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Rawicz W, Olbrich KC, McIntosh T, Needham D, Evans E. Effect of chain length and unsaturation on elasticity of lipid bilayers. Biophys J 2000; 79:328-39. [PMID: 10866959 PMCID: PMC1300937 DOI: 10.1016/s0006-3495(00)76295-3] [Citation(s) in RCA: 1370] [Impact Index Per Article: 57.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Micropipette pressurization of giant bilayer vesicles was used to measure both elastic bending k(c) and area stretch K(A) moduli of fluid-phase phosphatidylcholine (PC) membranes. Twelve diacyl PCs were chosen: eight with two 18 carbon chains and degrees of unsaturation from one double bond (C18:1/0, C18:0/1) to six double bonds per lipid (diC18:3), two with short saturated carbon chains (diC13:0, diC14:0), and two with long unsaturated carbon chains (diC20:4, diC22:1). Bending moduli were derived from measurements of apparent expansion in vesicle surface area under very low tensions (0.001-0.5 mN/m), which is dominated by smoothing of thermal bending undulations. Area stretch moduli were obtained from measurements of vesicle surface expansion under high tensions (>0.5 mN/m), which involve an increase in area per molecule and a small-but important-contribution from smoothing of residual thermal undulations. The direct stretch moduli varied little (< +/-10%) with either chain unsaturation or length about a mean of 243 mN/m. On the other hand, the bending moduli of saturated/monounsaturated chain PCs increased progressively with chain length from 0.56 x 10(-19) J for diC13:0 to 1.2 x 10(-19) J for diC22:1. However, quite unexpectedly for longer chains, the bending moduli dropped precipitously to approximately 0.4 x 10(-19) J when two or more cis double bonds were present in a chain (C18:0/2, diC18:2, diC18:3, diC20:4). Given nearly constant area stretch moduli, the variations in bending rigidity with chain length and polyunsaturation implied significant variations in thickness. To test this hypothesis, peak-to-peak headgroup thicknesses h(pp) of bilayers were obtained from x-ray diffraction of multibilayer arrays at controlled relative humidities. For saturated/monounsaturated chain bilayers, the distances h(pp) increased smoothly from diC13:0 to diC22:1 as expected. Moreover, the distances and elastic properties correlated well with a polymer brush model of the bilayer that specifies that the elastic ratio (k(c)/K(A))(1/2) = (h(pp) - h(o))/24, where h(o) approximately 1 nm accounts for separation of the headgroup peaks from the deformable hydrocarbon region. However, the elastic ratios and thicknesses for diC18:2, diC18:3, and diC20:4 fell into a distinct group below the correlation, which showed that poly-cis unsaturated chain bilayers are thinner and more flexible than saturated/monounsaturated chain bilayers.
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Affiliation(s)
- W Rawicz
- Department of Pathology, University of British Columbia, Vancouver, British Columbia V6T 1W5, Canada
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340
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Heimburg T. Monte Carlo simulations of lipid bilayers and lipid protein interactions in the light of recent experiments. Curr Opin Colloid Interface Sci 2000. [DOI: 10.1016/s1359-0294(00)00059-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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341
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Abstract
The architecture of cells, with various membrane-bound compartments and with the protein synthesizing machinery confined to one location, dictates that many proteins have to be transported through one or more membranes during their biogenesis. A lot of progress has been made on the identification of protein translocation machineries and their sorting signals in various organelles and organisms. Biochemical characterization has revealed the functions of several individual protein components. Interestingly, lipid components were also found to be essential for the correct functioning of these translocases. This led to the idea that there is a very intimate relationship between the lipid and protein components that enables them to fulfil their intriguing task of transporting large biopolymers through a lipid bilayer without leaking their contents. In this review we focus on the Sec translocases in the endoplasmic reticulum and the bacterial inner membrane. We also highlight the interactions of lipids and proteins during the process of translocation and integrate this into a model that enables us to understand the role of membrane lipid composition in translocase function.
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Affiliation(s)
- F Van Voorst
- Department of Biochemistry of Membranes, CBLE, Institute Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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342
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Epand RM, Epand RF, Decicco A, Schwarz D. Curvature properties of novel forms of phosphatidylcholine with branched acyl chains. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:2909-15. [PMID: 10806388 DOI: 10.1046/j.1432-1327.2000.01304.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We studied the properties of a series of phosphatidylcholine molecules with branched acyl chains. These lipids have previously been shown to have marked stimulatory effects on the side-chain cleavage activity of cytochrome P450SCC (CYP11A1), an enzyme of the inner mitochondrial membrane. The synthetic lipids used were diacyl phosphatidylcholines with the decanoyl, dodecanoyl or tetradecanoyl chain having a hexyl, octyl or decyl straight chain aliphatic branch at the 2-position. All three lipids lowered the bilayer to hexagonal phase transition temperature of dielaidoyl phosphatidylethanolamine, the lipids with longer acyl chains being more effective in this regard. As pure lipids all of the forms were found by X-ray diffraction to be predominantly in the hexagonal phase (HII) over the entire temperature range of 7-75 degrees C. The properties of the HII phase were unusual with regard to the small size of the lattice spacings and the small temperature dependence of the spacings. We used tetradecane to relieve hydrocarbon packing constraints to determine the intrinsic radius of curvature of the lipid monolayer. The elastic bending modulus was measured in the presence of tetradecane by introducing an osmotic gradient across the hexagonal phase cylinders with aqueous solutions of poly(ethylene glycol). The elastic bending modulus was found to be higher than that observed with other lipids and to increase with temperature. Both the small intrinsic radius of curvature and the high elastic bending modulus indicate that the presence of these lipids in bilayer membranes will impose a high degree of negative curvature strain.
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Affiliation(s)
- R M Epand
- Department of Biochemistry, McMaster University Health Sciences Center, Hamilton, Canada.
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343
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Kim KS, Neu J, Oster G. Effect of protein shape on multibody interactions between membrane inclusions. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 61:4281-5. [PMID: 11088224 DOI: 10.1103/physreve.61.4281] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/1999] [Revised: 11/19/1999] [Indexed: 04/29/2023]
Abstract
The elastic interaction of membrane inclusions provides one of the simplest physical realizations of multibody forces. Here we show how the cross-sectional shape of the inclusion greatly changes the character of the interaction, and illustrates a pattern formation mechanism. The formalism provides a transparent framework for modeling bilayer-inclusion boundary effects on the multibody interaction.
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Affiliation(s)
- K S Kim
- Department of Physics, Graduate Group in Theoretical Biophysics, University of California, Berkeley, California 94720, USA.
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344
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Koubi L, Tarek M, Klein ML, Scharf D. Distribution of halothane in a dipalmitoylphosphatidylcholine bilayer from molecular dynamics calculations. Biophys J 2000; 78:800-11. [PMID: 10653792 PMCID: PMC1300682 DOI: 10.1016/s0006-3495(00)76637-9] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
We report a 2-ns constant pressure molecular dynamics simulation of halothane, at a mol fraction of 50%, in the hydrated liquid crystal bilayer phase of dipalmitoylphosphatidylcholine. Halothane molecules are found to preferentially segregate to the upper part of the lipid acyl chains, with a maximum probability near the C(5) methylene groups. However, a finite probability is also observed along the tail region and across the methyl trough. Over 95% of the halothane molecules are located below the lipid carbonyl carbons, in agreement with photolabeling experiments. Halothane induces lateral expansion and a concomitant contraction in the bilayer thickness. A decrease in the acyl chain segment order parameters, S(CD), for the tail portion, and a slight increase for the upper portion compared to neat bilayers, are in agreement with several NMR studies on related systems. The decrease in S(CD) is attributed to a larger accessible volume per lipid in the tail region. Significant changes in the electric properties of the lipid bilayer result from the structural changes, which include a shift and broadening of the choline headgroup dipole (P-N) orientation distribution. Our findings reconcile apparent controversial conclusions from experiments on diverse lipid systems.
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Affiliation(s)
- L Koubi
- Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, Philadelphia 19104-6323, USA
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345
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Cantor RS. Solute modulation of conformational equilibria in intrinsic membrane proteins: apparent "cooperativity" without binding. Biophys J 1999; 77:2643-7. [PMID: 10545364 PMCID: PMC1300538 DOI: 10.1016/s0006-3495(99)77098-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The activity of many membrane proteins depends on a conformational transition that is often strongly influenced by small membrane-soluble solutes. This allosteric modulation may be direct, involving binding to the protein at localized sites of varying specificity, or may be indirect, resulting from altered membrane properties. In the present paper, a general expression for solute-protein titration curves is predicted, using an indirect mechanism that couples solute-induced changes in the lateral pressure profile of the bilayer to a shift in protein conformational equilibrium. When the common practice of fitting dose-response data to the Hill equation is applied to these curves, the fits are found to be reasonably good, with large Hill coefficients. Because this would commonly be interpreted as evidence of the existence of multiple sites with strong positive cooperativity, it is argued that caution must therefore be exercised in the interpretation of titration data in the absence of direct evidence of the existence of binding sites. The form of the titration curve predicted from this lateral pressure mechanism is shown to be quite general for indirect mechanisms. It is also shown that this form is the same as would be obtained from classical models of binding cooperativity, such as that of Monod, Wyman, and Changeux, in the limit of an infinite number of sites with vanishingly small site affinity.
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Affiliation(s)
- R S Cantor
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA.
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346
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Cantor RS. The influence of membrane lateral pressures on simple geometric models of protein conformational equilibria. Chem Phys Lipids 1999; 101:45-56. [PMID: 10810924 DOI: 10.1016/s0009-3084(99)00054-7] [Citation(s) in RCA: 165] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The function of many intrinsic membrane proteins requires a conformational transition that is often strongly influenced by the molecular composition of the bilayer in which the protein is embedded. Recently, a mechanism for this shift in conformational equilibrium was suggested, in which it is argued that a shift in distribution of lateral pressures of the bilayer resulting from a change in lipid composition alters the amount of mechanical work of the protein conformational transition, if the change in the cross-sectional area profile of the protein varies with depth within the bilayer. As there is little information on the change in shape of the transmembrane region of any protein, various simple geometric models are considered. For both a generic model, and more specific models that approximate likely cooperative rearrangements of alpha-helices in bundles, it is found that the conformational equilibrium depends on the first and second integral moments of the lateral pressure distribution. In addition to revealing the possible physical underpinnings of the well-known correlation between protein activity and the 'nonlamellar' tendency of bilayer lipids, this dependence on moments of the pressure profile allows for prediction of the relative effects of different lipid compositional changes even in the absence of information on specific protein shape changes. Effects of variation in acyl chain length, degree and position of cis-unsaturation, and addition of cholesterol and small interfacially-active solutes (n-alkanols) are compared.
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Affiliation(s)
- R S Cantor
- Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA.
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