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1.
Phys Chem Chem Phys ; 22(9): 5255-5263, 2020 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-32091512

RESUMO

Currently, membrane curvature is understood as an active mechanism to control cells spatial organization and activity. Protein processes involved in sensing and generating curvature are therefore of major interest. In this work, we have studied α-synuclein interactions with a model lipid bilayer, inducing curvature in a controlled manner and describing protein responses at molecular level. We show that the intrinsically disordered region of α-synuclein binds to the bilayer as an acknowledgment to the induced curvature, a mechanism used by the interacting protein-membrane assembly to relieve free energy. We have calculated free energies for bending the bilayer with α-synuclein adsorbed on the surface and we have established the crucial role of the intrinsically disordered region, suggesting that a dynamic order/disorder interplay takes place as the bilayer reorganizes to bend.


Assuntos
Bicamadas Lipídicas/química , alfa-Sinucleína/química , Bicamadas Lipídicas/metabolismo , Modelos Teóricos , Ligação Proteica , Propriedades de Superfície , Termodinâmica , alfa-Sinucleína/metabolismo
2.
Mol Pharmacol ; 97(4): 295-303, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-32102968

RESUMO

The main objective of this study was to clarify the topical mechanisms underlying diclofenac-induced gastric toxicity by considering for the first time both ionization states of this nonsteroidal anti-inflammatory drug. 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes were the model system chosen to mimic the protective phospholipid layers of the gastric mucosa and to describe the interactions with diclofenac, considering the pH gradient found in the gastric mucosa (3 < pH < 7.4). Complementary experimental techniques were combined to evaluate the drug's affinity for DMPC bilayers, as well as to assess the drug's effects on the structural properties of the phospholipid bilayer. The diclofenac-DMPC interactions were clearly dependent on the drug's ionization state. Neutral diclofenac displayed greater affinity for DMPC bilayers than anionic diclofenac. Moreover, the protonated/neutral form of the drug induced more pronounced and/or distinct alterations in the structure of the DMPC bilayer than the deprotonated/ionized form, considering similar membrane concentrations. Therefore, neutral diclofenac-induced changes in the structural properties of the external phospholipid layers of the gastric mucosa may constitute an additional toxicity mechanism of this worldwide-used drug, which shall be considered for the development of safer therapeutic strategies. SIGNIFICANCE STATEMENT: Neutral or anionic diclofenac exerted distinct alterations in phosphatidylcholine bilayers, which are used in this work as models for the protective phospholipid layers of the gastric mucosa. Remarkable changes were induced by neutral diclofenac in the structural properties of the phospholipid bilayer, suggesting that both ionized and neutral states of nonsteroidal anti-inflammatory drugs must be considered to clarify their mechanisms of toxicity and to ultimately develop safer anti-inflammatory drugs.


Assuntos
Anti-Inflamatórios não Esteroides/toxicidade , Diclofenaco/toxicidade , Dimiristoilfosfatidilcolina/química , Mucosa Gástrica/efeitos dos fármacos , Bicamadas Lipídicas/química , Mucosa Gástrica/química , Concentração de Íons de Hidrogênio , Lipossomos/química , Estrutura Molecular , Espalhamento a Baixo Ângulo , Difração de Raios X
3.
Phys Rev Lett ; 124(3): 038001, 2020 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-32031854

RESUMO

Cholesterol is a crucial component of mammalian cell membranes that takes part in many vital processes. It is generally accepted that cholesterol stabilizes the membrane and induces transitions into ordered states. In contrast to expectations, we demonstrate that cholesterol can destabilize the membrane by creating a nanodomain around a perpendicularly embedded ultrashort carbon nanotube (CNT), and we show that cholesterol triggers the translocation of an ultrashort CNT through the cell membrane. Using atomistic simulations, we report the existence of a nanoscale domain around an ultrashort carbon nanotube within a crossover distance of 0.9 nm from the surface of the nanotube, where the properties of the bilayer are different from the bulk: the domain is characterized by increased fluctuations, increased thickness, and increased order of the lipids with respect to the bulk. Cholesterol decreases the thickness and order of lipids and increases the fluctuations with respect to a pure lipid bilayer. Experimentally, we confirm that cholesterol nanodomains provoke spontaneous translocation of nanotubes through a lipid bilayer even for low membrane tensions. A specially designed microfluidic device allows us to trace the kinetic pathway of the translocation process and establish the threshold cholesterol concentration of 20% for translocation. The reported nanoscale cholesterol-induced membrane restructuring near the ultrashort CNT in lipid membranes enables precise control and specific targeting of a membrane using cholesterol. As an example, it may allow for specific targeting between cholesterol-rich mammalian cells and cholesterol-poor bacterial cells.


Assuntos
Membrana Celular/química , Colesterol/química , Lipídeos de Membrana/química , Modelos Químicos , Nanotubos de Carbono/química , Membrana Celular/metabolismo , Colesterol/metabolismo , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Lipídeos de Membrana/metabolismo , Modelos Biológicos
4.
Chem Commun (Camb) ; 56(21): 3147-3150, 2020 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-32057047

RESUMO

Amyloid fibrils, implicated in health and diseases, commonly exhibit a periodic twist trait relevant to the structures and dynamics of the fibrils. However, the origins and modulations of fibril twist in complex in vivo environments are not yet fully understood. Here we highlight an important factor that causes twist variations in amyloid fibril structures-the presence of surrounding surfaces. Using cholesterol-containing lipid bilayers with varying cholesterol contents, we have demonstrated via atomic force microscopy that amyloid-ß peptide fibrils initiated on membranes increase their average pitch size of twisting periodicity as the cholesterol content increases. These surface-induced twist variations arise from the enhanced hydrophobic interactions between the fibril and the surface distorting the torsional elastic energy of the fibril twisting as supported by a theory of an elastic model. These findings not only provide an important insight into fibril polymorphism phenomena resulting from the surface effects but also suggest a novel solution to modulate filament twisting on the nanoscale for biomaterials applications involving nanoscale features.


Assuntos
Amiloide/química , Colesterol/química , Bicamadas Lipídicas/química , Microscopia de Força Atômica , Tamanho da Partícula , Conformação Proteica , Propriedades de Superfície
5.
Phys Chem Chem Phys ; 22(6): 3234-3244, 2020 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-31994545

RESUMO

In the present contribution, we investigate the interactions of lipid bilayer membranes of different charges and different phase states with aliphatic amino acids of varying charge (aspartic acid, glutamic acid, arginine and lysine) and hydrophobicity (serine, leucine and valine) by steady state and time-resolved spectroscopic techniques, dynamic light scattering (DLS) measurements and confocal imaging (CLSM). The study reveals that negatively charged amino acids such as aspartic acid and glutamic acid interact strongly with the lipid membranes particularly with negatively charged lipid membranes by stabilizing their gel phase. On the other hand, positively charged amino acids bring in hydration in the membranes. We explain this unique observation by the shift in pKa of amino acids in the vicinity of the lipid membranes and solvation and desolvation processes in the light of recent computer simulations. We also find that hydrogen bonding plays a significant role in governing the interaction of aliphatic amino acids with zwitterionic lipid membranes. The more polar serine bearing a hydroxyl group at the terminal carbon offers a stronger interaction with the lipid bilayer membranes as compared to its analogues leucine and valine, which are hydrophobic in nature.


Assuntos
Aminoácidos/química , Bicamadas Lipídicas/química , Simulação por Computador , Desidratação , Ligação de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Íons/química , Cinética , Modelos Moleculares , Estrutura Molecular , Relação Estrutura-Atividade
6.
Chem Commun (Camb) ; 56(11): 1653-1656, 2020 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-31939470

RESUMO

Distinct annexin V binding behaviours in Ca2+-dependent and Ca2+-independent cases were comparatively investigated using sum frequency generation vibrational spectroscopy. It was discovered that binding affected the molecular arrangement of both membrane leaflets, and the initial Ca2+-independent binding went through a transition with annexin V reorientation to a more stable state upon adding Ca2+.


Assuntos
Anexina A5/metabolismo , Cálcio/metabolismo , Bicamadas Lipídicas/metabolismo , 1,2-Dipalmitoilfosfatidilcolina/química , Bicamadas Lipídicas/química , Fosfatidilcolinas/química , Fosfatidilserinas/química , Ligação Proteica , Análise Espectral/métodos , Vibração , Água/química
7.
Bioelectrochemistry ; 132: 107416, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31981968

RESUMO

A hybrid bilayer lipid membrane (hBLM), constructed with a 1-hexadecanethiol self-assembled interior leaflet and a 1,2-dipalmitoyl-sn-glycero-3-cytidine nucleolipid exterior leaflet, was deposited at the surface of a gold (111) electrode. This system was used to investigate the molecular recognition reaction between the cytosine moieties of the lipid head group with guanine molecules in the bulk electrolyte solution. Electrochemical measurements and photon polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) were employed to characterize the system and determine the extent of the molecular recognition reaction. The capacitance of the hBLM-covered gold electrode was very low (~1 µF cm-2), therefore the charge density at the gold surface was small. Changing the electrode potential had a minimal effect on the complexation between the cytosine moieties and guanine molecules due to small changes in the static electric field across the membrane. This behavior favored the formation of the guanine-cytosine complex.


Assuntos
Citosina/química , Eletrodos , Ouro/química , Guanina/química , Bicamadas Lipídicas/química , Espectrofotometria Infravermelho
8.
PLoS One ; 15(1): e0227562, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31935248

RESUMO

We study the time evolution of the shape of a vesicle membrane under time-dependent spontaneous curvature by means of phase-field model. We introduce the variation in time of the spontaneous curvature via a second field which represents the concentration of a substance that anchors with the lipid bilayer thus changing the local curvature and producing constriction. This constriction is mediated by the action on the membrane of an structure resembling the role of a Z ring. Our phase-field model is able to reproduce a number of different shapes that have been experimentally observed. Different shapes are associated with different constraints imposed upon the model regarding conservation of membrane area. In particular, we show that if area is conserved our model reproduces the so-called L-form shape. By contrast, if the area of the membrane is allowed to grow, our model reproduces the formation of a septum in the vicinity of the constriction. Furthermore, we propose a new term in the free energy which allows the membrane to evolve towards eventual pinching.


Assuntos
Lipossomos/química , Modelos Biológicos , Bicamadas Lipídicas/química , Tensão Superficial , Termodinâmica
9.
Nat Commun ; 11(1): 230, 2020 01 13.
Artigo em Inglês | MEDLINE | ID: mdl-31932647

RESUMO

Annexins are abundant cytoplasmic proteins, which bind to membranes that expose negatively charged phospholipids in a Ca2+-dependent manner. During cell injuries, the entry of extracellular Ca2+ activates the annexin membrane-binding ability, subsequently initiating membrane repair processes. However, the mechanistic action of annexins in membrane repair remains largely unknown. Here, we use high-speed atomic force microscopy (HS-AFM), fluorescence recovery after photobleaching (FRAP), confocal laser scanning microscopy (CLSM) and molecular dynamics simulations (MDSs) to analyze how annexin-V (A5) binds to phosphatidylserine (PS)-rich membranes leading to high Ca2+-concentrations at membrane, and then to changes in the dynamics and organization of lipids, eventually to a membrane phase transition. A5 self-assembly into lattices further stabilizes and likely structures the membrane into a gel phase. Our findings are compatible with the patch resealing through vesicle fusion mechanism in membrane repair and indicate that A5 retains negatively charged lipids in the inner leaflet in an injured cell.


Assuntos
Anexina A5/metabolismo , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Anexina A5/química , Cálcio/metabolismo , Recuperação de Fluorescência Após Fotodegradação , Fusão de Membrana , Microscopia de Força Atômica , Microscopia Confocal , Simulação de Dinâmica Molecular , Transição de Fase , Fosfatidilserinas/química , Fosfatidilserinas/metabolismo , Agregados Proteicos
10.
Nat Commun ; 11(1): 469, 2020 01 24.
Artigo em Inglês | MEDLINE | ID: mdl-31980608

RESUMO

The selective transport of ions across cell membranes, controlled by membrane proteins, is critical for a living organism. DNA-based systems have emerged as promising artificial ion transporters. However, the development of stable and selective artificial ion transporters remains a formidable task. We herein delineate the construction of an artificial ionophore using a telomeric DNA G-quadruplex (h-TELO) and a lipophilic guanosine (MG). MG stabilizes h-TELO by non-covalent interactions and, along with the lipophilic side chain, promotes the insertion of h-TELO within the hydrophobic lipid membrane. Fluorescence assays, electrophysiology measurements and molecular dynamics simulations reveal that MG/h-TELO preferentially transports K+-ions in a stimuli-responsive manner. The preferential K+-ion transport is presumably due to conformational changes of the ionophore in response to different ions. Moreover, the ionophore transports K+-ions across CHO and K-562 cell membranes. This study may serve as a design principle to generate selective DNA-based artificial transporters for therapeutic applications.


Assuntos
Quadruplex G , Transporte de Íons , Nucleosídeos/química , Ionóforos de Potássio/química , Animais , Células CHO , Cricetulus , Humanos , Células K562 , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Simulação de Dinâmica Molecular , Estrutura Molecular , Nucleosídeos/síntese química , Ionóforos de Potássio/síntese química , Espectrometria de Fluorescência
11.
J Phys Chem Lett ; 11(4): 1204-1208, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-31944770

RESUMO

Biological transmission of vesicular content occurs by opening of a fusion pore. Recent experimental observations have illustrated that fusion pores between vesicles that are docked by an extended flat contact zone are located at the edge (vertex) of this zone. We modeled this experimentally observed scenario by coarse-grained molecular simulations and elastic theory. This revealed that fusion pores experience a direct attraction toward the vertex. The size adopted by the resulting vertex pore strongly depends on the apparent contact angle between the adhered vesicles even in the absence of membrane surface tension. Larger contact angles substantially increase the equilibrium size of the vertex pore. Because the cellular membrane fusion machinery actively docks membranes, it facilitates a collective expansion of the contact zone and increases the contact angle. In this way, the fusion machinery can drive expansion of the fusion pore by free energy equivalents of multiple tens of kBT from a distance and not only through the fusion proteins that reside within the fusion pore.


Assuntos
Bicamadas Lipídicas/metabolismo , Fusão de Membrana/fisiologia , Modelos Biológicos , Microscopia Crioeletrônica , Bicamadas Lipídicas/química , Simulação de Dinâmica Molecular , Proteínas SNARE/química , Proteínas SNARE/metabolismo , Termodinâmica , Lipossomas Unilamelares/química , Lipossomas Unilamelares/metabolismo
12.
Chemphyschem ; 21(1): 9-12, 2020 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-31483076

RESUMO

Whilst the formation of plastic nanoparticles (nanoplastics) from plastic wastes has been unequivocally evidenced, little is known about the effects of these materials on living organisms at the subcellular or molecular levels. In the present contribution we show through molecular dynamics simulations that polyethylene nanoparticles dissolve in the hydrophobic core of lipid bilayers into a network of disentangled, single polymeric chains. The thereby induced structural and dynamic changes in the bilayer alter vital functions of the cell membrane, which if lacking a mechanism to decompose the polymer chains may result in the death of the cell.


Assuntos
Membrana Celular/química , Bicamadas Lipídicas/química , Nanopartículas/química , Polietileno/química , Interações Hidrofóbicas e Hidrofílicas , Simulação de Dinâmica Molecular
13.
J Chem Theory Comput ; 16(1): 782-793, 2020 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-31751511

RESUMO

We present a coarse-grained (CG) force field (FF), pSPICA, for lipid membranes that incorporates a CG polar water model, which guarantees a reasonable dielectric response for water. Using a relatively simple functional form for the interaction, the CG parameters were systematically optimized to reproduce surface/interfacial tension, density, solvation or transfer free energy, as well as distribution functions obtained from all-atom molecular dynamics trajectory generated with the CHARMM FF, following the scheme used in the SPICA FF. Lipid membranes simulated using the present CG FF demonstrate reasonable membrane area and thickness, elasticity, and line tension, which ensure that the simulated lipid membranes exhibit proper mesoscopic morphology. The major advantages of the pSPICA FF with a polar water model were its ability to simulate membrane electroporation and its superior performance in the morphological characterization of charged lipid aggregates. We also demonstrated that the pSPICA can better describe the membrane permeation of hydrophilic segments involving a water string formation.


Assuntos
Lipídeos de Membrana/química , Água/química , Alcanos/química , Eletroporação , Bicamadas Lipídicas/química , Simulação de Dinâmica Molecular , Termodinâmica
14.
J Chem Theory Comput ; 16(1): 711-724, 2020 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-31765139

RESUMO

Surfactant micelles are often utilized as membrane mimetics for structure determination and functional analysis of membrane proteins. The curved-surface effects of the micelle can perturb membrane protein structure. However, it is difficult to assess such effects and membrane mimetic artifacts by experimental and theoretical methods. Here, we propose an implicit micelle model (IMIC) to be used in molecular dynamics (MD) simulations of membrane proteins. IMIC is an extension of the IMM1 implicit membrane model and additionally introduces a superellipsoid approximation to represent the curved-surface effects. Most of the IMIC parameters are obtained from all-atom explicit solvent MD simulations of 12 membrane proteins in various micelles. The HIV envelope protein gp41, M13 major coat protein gp8, and amyloid precursor protein (APP) dimer are simulated via MD simulations with IMIC. These simulations clearly show how the micelle influences membrane protein structures compared to the bilayer environments. The MD simulations with IMIC provide reliable membrane protein structures in various micelle environments quickly with smaller computational cost than that for an explicit solvent/micelle model.


Assuntos
Proteínas de Membrana/química , Simulação de Dinâmica Molecular , Bicamadas Lipídicas/química , Micelas , Modelos Moleculares , Conformação Proteica , Termodinâmica , Água/química
15.
Biophys Chem ; 257: 106275, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31790909

RESUMO

We performed molecular dynamics simulations of a lipid bilayer consisting of POPC and cholesterol at temperatures from 283 to 308K and cholesterol concentrations from 0 to 50% mol/mol. The purpose of this study was to look for the existence of structural differences in the region delimited by these parameters and, in particular, in a region where coexistence of liquid disordered and liquid ordered phases has been proposed. Our interest in this range of concentration and temperature responds to the fact that polyene ionophore activity varies considerably along it. Two force fields, CHARMM36 and Slipids, were compared in order to determine the most suitable. Both force fields predict non-monotonic behaviors consistent with the existence of phase transitions. We found the presence of lateral structural heterogeneity, statistical in nature, in some of the bilayers occurring in this range of temperatures and sterol concentrations. This heterogeneity was produced by correlated ordering of the POPC tails and not due to cholesterol enrichment, and lasts for tens of nanoseconds. We relate these observations to the action of polyenes in these membranes.


Assuntos
Colesterol/química , Bicamadas Lipídicas/química , Simulação de Dinâmica Molecular , Fosfatidilcolinas/química , Microscopia de Força Atômica , Transição de Fase , Temperatura
16.
J Chem Theory Comput ; 16(1): 749-764, 2020 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-31639310

RESUMO

Thorough computational description of the properties of membrane-anchored protein receptors, which are important for example in the context of active targeting drug delivery, may be achieved by models representing as close as possible the immediate environment of these macromolecules. An all-atom bilayer, including 35 different lipid types asymmetrically distributed among the two monolayers, is suggested as a model neoplastic cell membrane. One molecule of folate receptor-α (FRα) is anchored into its outer leaflet, and the behavior of the system is explored by atomistic molecular dynamics simulations. The total number of atoms in the model is ∼185 000. Three 1-µs-long simulations are carried out, where physiological conditions (310 K and 1 bar) are maintained with three different pressure scaling schemes. To evaluate the structure and the phase state of the membrane, the density profiles of the system, the average area per lipid, and the deuterium order parameter of the lipid tails are calculated. The bilayer is in liquid ordered state, and the specific arrangement varies between the three trajectories. The changes in the structure of FRα are investigated and are found time- and ensemble-dependent. The volume of the ligand binding pocket fluctuates with time, but this variation remains independent of the more global structural alterations. The latter are mostly "waving" motions of the protein, which periodically approaches and retreats from the membrane. The semi-isotropic pressure scaling perturbs the receptor most significantly, while the isotropic algorithm induces rather slow changes. Maintaining constant nonzero surface tension leads to behavior closest to the experimentally observed one.


Assuntos
Receptor 1 de Folato/química , Bicamadas Lipídicas/química , Sítios de Ligação , Cristalografia por Raios X , Humanos , Simulação de Dinâmica Molecular , Conformação Proteica , Estrutura Secundária de Proteína
17.
Phys Chem Chem Phys ; 22(3): 1242-1249, 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31850441

RESUMO

A supported lipid bilayer (SLB) is now an indispensable tool to analyze the dynamical properties of biomembranes. However, the effect of a solid support on the leaflet-specific lipid dynamics in a SLB remains elusive, which hampers the further application of the SLB as a model biomembrane. Here, we performed the leaflet-specific lipid diffusion analysis by means of two-dimensional fluorescence lifetime correlation spectroscopy to elucidate the effect of the electrostatic interaction between lipid headgroups and a glass surface on the lipid diffusion in each leaflet of the SLB. The results clearly showed the correlation between the strength of the electrostatic interaction and the lipid diffusion in the proximal leaflet of the SLB facing a glass surface. In particular, the electrostatic attraction between the cationic lipids and a negatively charged glass surface enhanced the lipid diffusion in the proximal leaflet of the SLB, providing important implications for the lipid dynamics not only in the SLB but also in biomembranes.


Assuntos
Bicamadas Lipídicas/química , Modelos Químicos , Eletricidade Estática , Difusão , Fluorescência
18.
Spectrochim Acta A Mol Biomol Spectrosc ; 224: 117329, 2020 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-31326855

RESUMO

Visualization of membrane domains like lipid rafts in natural or artificial membranes is a crucial task for cell biology. For this purpose, fluorescence microscopy is often used. Since fluorescing probes in lipid membranes partition specifically in e.g. local liquid disordered or liquid ordered environments, the consequent changes in their orientation and location are both theoretically and experimentally of interest. Here we focused on a liquid disordered membrane phase and performed molecular dynamics (MD) simulations of the indocarbocyanine DiD probes by varying the length of the attached alkyl tails and also the length of the cyanine backbone. From the probed compounds in a DOPC lipid bilayer at ambient temperature, a varying orientation of the transition dipole moment was observed, which is crucial for fluorescence microscopy and which, through photoselection, was found to be surprisingly more effective for asymmetric probes than for the symmetric ones. Furthermore, we observed that the orientation of the probes was dependent on the tail length; with the methyls or propyls attached, DiD oriented with its tails facing the water, contrary to the ones with longer tails. With advanced hybrid QM/MM calculations we show that the different local environment for differently oriented probes affected the one-photon absorption spectra, that was blue-shifted for the short-tailed DiD with respect to the DiDs with longer tails. We show here that the presented probes can be successfully used for fluorescence microscopy and we believe that the described properties bring further insight for the experimental use of these probes.


Assuntos
Carbocianinas/química , Corantes Fluorescentes/química , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Simulação de Dinâmica Molecular , Espectrometria de Fluorescência
19.
Bioelectrochemistry ; 132: 107443, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31869700

RESUMO

Planar asymmetric lipid bilayers composed of phosphatidylethanolamine and phosphatidylglycerol lipids are transferred onto a gold electrode surface. Lipids containing two saturated, one monounsaturated and two monounsaturated hydrocarbon chains compose the model membranes. Results of electrochemically controlled polarization modulation infrared reflection absorption spectroscopy and quartz crystal microbalance with energy dissipation studies reveal two different types of electric potential-dependent structural rearrangements in the bilayers. They are correlated with the geometry of the lipid molecule. Packing parameter correlates the cross-section area of the hydrophobic and hydrophilic parts of amphiphilic molecules. In bilayers composed of lipids with the packing parameter <1, the hydrocarbon chains are tilted with respect to the bilayer plane and the polar head groups are well hydrated. At a threshold potential an abrupt flow of water through the bilayer is connected with membrane dehydration and upward orientation of the chains. In bilayers composed of lipids with packing parameter ≥1, electric potentials have negligible effect on the membrane structure. A simple rule correlating the packing parameter with molecular scale changes occurring at electrified membranes has a large diagnostic implication for biomimetic studies and our understanding of molecular processes occurring in biological cell membranes.


Assuntos
Eletrodos , Lipídeos/química , Membranas Artificiais , Interações Hidrofóbicas e Hidrofílicas , Bicamadas Lipídicas/química , Espectrofotometria Infravermelho/métodos
20.
Nat Struct Mol Biol ; 27(1): 62-70, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31873305

RESUMO

ABCB4 is an ATP-binding cassette transporter that extrudes phosphatidylcholine into the bile canaliculi of the liver. Its dysfunction or inhibition by drugs can cause severe, chronic liver disease or drug-induced liver injury. We determined the cryo-EM structure of nanodisc-reconstituted human ABCB4 trapped in an ATP-bound state at a resolution of 3.2 Å. The nucleotide binding domains form a closed conformation containing two bound ATP molecules, but only one of the ATPase sites contains bound Mg2+. The transmembrane domains adopt a collapsed conformation at the level of the lipid bilayer, but we observed a large, hydrophilic and fully occluded cavity at the level of the cytoplasmic membrane boundary, with no ligand bound. This indicates a state following substrate release but prior to ATP hydrolysis. Our results rationalize disease-causing mutations in human ABCB4 and suggest an 'alternating access' mechanism of lipid extrusion, distinct from the 'credit card swipe' model of other lipid transporters.


Assuntos
Subfamília B de Transportador de Cassetes de Ligação de ATP/química , Subfamília B de Transportador de Cassetes de Ligação de ATP/metabolismo , Subfamília B de Transportador de Cassetes de Ligação de ATP/ultraestrutura , Trifosfato de Adenosina/metabolismo , Sítios de Ligação , Microscopia Crioeletrônica , Humanos , Hidrólise , Bicamadas Lipídicas/química , Modelos Moleculares , Conformação Proteica , Especificidade por Substrato
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