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3.
Nat Nanotechnol ; 15(1): 73-79, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31844288

RESUMO

Artificial water channels are synthetic molecules that aim to mimic the structural and functional features of biological water channels (aquaporins). Here we report on a cluster-forming organic nanoarchitecture, peptide-appended hybrid[4]arene (PAH[4]), as a new class of artificial water channels. Fluorescence experiments and simulations demonstrated that PAH[4]s can form, through lateral diffusion, clusters in lipid membranes that provide synergistic membrane-spanning paths for a rapid and selective water permeation through water-wire networks. Quantitative transport studies revealed that PAH[4]s can transport >109 water molecules per second per molecule, which is comparable to aquaporin water channels. The performance of these channels exceeds the upper bound limit of current desalination membranes by a factor of ~104, as illustrated by the water/NaCl permeability-selectivity trade-off curve. PAH[4]'s unique properties of a high water/solute permselectivity via cooperative water-wire formation could usher in an alternative design paradigm for permeable membrane materials in separations, energy production and barrier applications.

4.
Nat Nanotechnol ; 14(12): 1129-1134, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31740796

RESUMO

The ability of cells or cell components to move in response to chemical signals is critical for the survival of living systems. This motion arises from harnessing free energy from enzymatic catalysis. Artificial model protocells derived from phospholipids and other amphiphiles have been made and their enzymatic-driven motion has been observed. However, control of directionality based on chemical cues (chemotaxis) has been difficult to achieve. Here we show both positive or negative chemotaxis of liposomal protocells. The protocells move autonomously by interacting with concentration gradients of either substrates or products in enzyme catalysis, or Hofmeister salts. We hypothesize that the propulsion mechanism is based on the interplay between enzyme-catalysis-induced positive chemotaxis and solute-phospholipid-based negative chemotaxis. Controlling the extent and direction of chemotaxis holds considerable potential for designing cell mimics and delivery vehicles that can reconfigure their motion in response to environmental conditions.


Assuntos
Células Artificiais/metabolismo , Enzimas Imobilizadas/metabolismo , Lipossomos/metabolismo , Adenosina Trifosfatases/metabolismo , Animais , Catalase/metabolismo , Quimiotaxia , Humanos , Movimento (Física) , Fosfolipídeos/metabolismo , Urease/metabolismo
5.
Proc Natl Acad Sci U S A ; 116(32): 15784-15791, 2019 08 06.
Artigo em Inglês | MEDLINE | ID: mdl-31337677

RESUMO

Aqueous two-phase system (ATPS) formation is the macroscopic completion of liquid-liquid phase separation (LLPS), a process by which aqueous solutions demix into 2 distinct phases. We report the temperature-dependent kinetics of ATPS formation for solutions containing a monoclonal antibody and polyethylene glycol. Measurements are made by capturing dark-field images of protein-rich droplet suspensions as a function of time along a linear temperature gradient. The rate constants for ATPS formation fall into 3 kinetically distinct categories that are directly visualized along the temperature gradient. In the metastable region, just below the phase separation temperature, T ph , ATPS formation is slow and has a large negative apparent activation energy. By contrast, ATPS formation proceeds more rapidly in the spinodal region, below the metastable temperature, T meta , and a small positive apparent activation energy is observed. These region-specific apparent activation energies suggest that ATPS formation involves 2 steps with opposite temperature dependencies. Droplet growth is the first step, which accelerates with decreasing temperature as the solution becomes increasingly supersaturated. The second step, however, involves droplet coalescence and is proportional to temperature. It becomes the rate-limiting step in the spinodal region. At even colder temperatures, below a gelation temperature, T gel , the proteins assemble into a kinetically trapped gel state that arrests ATPS formation. The kinetics of ATPS formation near T gel is associated with a remarkably fragile solid-like gel structure, which can form below either the metastable or the spinodal region of the phase diagram.


Assuntos
Anticorpos Monoclonais/análise , Água/química , Coloides/química , Cinética , Espalhamento de Radiação , Soluções , Temperatura , Fatores de Tempo , Imagem com Lapso de Tempo
6.
J Am Chem Soc ; 141(17): 6930-6936, 2019 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-31010283

RESUMO

The anomalously high mobility of hydroxide and hydronium ions in aqueous solutions is related to proton transfer and structural diffusion. The role of counterions in these solutions, however, is often considered to be negligible. Herein, we explore the impact of alkali metal counter cations on hydroxide solvation and mobility. Impedance measurements demonstrate that hydroxide mobility is attenuated by lithium relative to sodium and potassium. These results are explained by ab initio molecular dynamics simulations and experimental vibrational hydration shell spectroscopy, which reveal substantially stronger ion pairing between OH- and Li+ than with other cations. Hydration shell spectra and theoretical vibrational frequency calculations together imply that lithium and sodium cations have different effects on the delocalization of water protons donating a hydrogen bond to hydroxide. Specifically, lithium leads to enhanced proton delocalization compared with sodium. However, proton delocalization and the overall diffusion process are not necessarily correlated.

7.
J Am Chem Soc ; 141(16): 6609-6616, 2019 04 24.
Artigo em Inglês | MEDLINE | ID: mdl-30919630

RESUMO

When a mixture of two salts in an aqueous solution contains a weakly and a strongly hydrated anion, their combined effect is nonadditive. Herein, we report such nonadditive effects on the lower critical solution temperature (LCST) of poly( N-isopropylacrylamide) (PNiPAM) for a fixed concentration of Na2SO4 and an increasing concentration of NaI. Using molecular dynamics simulations and vibrational sum frequency spectroscopy, we demonstrate that at low concentrations of the weakly hydrated anion (I-), the cations (Na+) preferentially partition to the counterion cloud around the strongly hydrated anion (SO42-), leaving I- more hydrated. However, upon further increase in the NaI concentration, this weakly hydrated anion is forced out of solution to the polymer/water interface by sulfate. Thus, the LCST behavior of PNiPAM involves competing roles for ion hydration and polymer-iodide interactions. This concept can be generally applied to mixtures containing both a strongly and a weakly hydrated anion from the Hofmeister series.

8.
Langmuir ; 35(3): 824-830, 2019 01 22.
Artigo em Inglês | MEDLINE | ID: mdl-30638371

RESUMO

Sphingosine-1-phosphate (S1P) is a sphingolipid metabolite that is thought to participate in the regulation of many physiological processes and may play a key role in several diseases. Herein, we found that Cu2+ binds tightly to supported lipid bilayers (SLBs) containing S1P. Specifically, we demonstrated via fluorescence assays that Cu2+-S1P binding was bivalent and sensitive to the concentration of S1P in the SLB. In fact, the apparent equilibrium dissociation constant, KDApp, tightened by a factor of 132 from 4.5 µM to 34 nM as the S1P density was increased from 5.0 to 20 mol %. A major driving force for this apparent tightening was the more negative surface potential with increasing S1P concentration. This potential remained unaltered upon Cu2+ binding at pH 7.4 because two protons were released for every Cu2+ that bound. At pH 5.4, however, Cu2+ could not outcompete protons for the amine and no binding occurred. Moreover, at pH 9.4, the amine was partially deprotonated before Cu2+ binding and the surface potential became more positive on binding. The results for Cu2+-S1P binding were reminiscent of those for Cu2+-phosphatidylserine binding, where a carboxylate group helped to deprotonate the amine. In the case of S1P, however, the phosphate needed to bear two negative charges to facilitate amine deprotonation in the presence of Cu2+.

9.
J Phys Chem B ; 122(51): 12260-12270, 2018 12 27.
Artigo em Inglês | MEDLINE | ID: mdl-30543432

RESUMO

The interfacial water structure and phosphate group hydration of 1,2-dioleoyl- sn-glycero-3-phosphatidylcholine monolayers were investigated at air/water interfaces. Both vibrational sum frequency spectroscopy (VSFS) and Langmuir monolayer compression measurements were made. The PC lipids oriented water molecules predominantly through their phosphate-choline (P-N) dipoles and carbonyl moieties. Upon the introduction of low concentrations of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), a positively charged double chain surfactant, the TAP headgroups were attracted to the phosphate moieties on adjacent PC lipids. This attraction caused the monolayers to contract, expelling water molecules that were hydrogen bonded to the phosphate groups. Moreover, amplitude of the OH stretch signal decreased. At higher DOTAP concentrations, the positive charge on the monolayer caused an increase in the area per headgroup and water molecules in the near-surface bulk region became increasingly aligned. Under these latter conditions, the OH stretch amplitude was linearly proportional to the surface potential. By contrast, introducing 1,2-dioleoyl- sn-glycero-3-phosphatidylglycerol, a negatively charged lipid, did not change the area per lipid or the phosphate-water hydrogen bonding network. As the interfacial potential grew more negative, the OH stretch amplitude increased continuously. Significantly, changes in the interfacial water spectrum were independent of the chemistry employed to create the positive or negative interfacial potential. For example, Ca2+ and tetracaine (both positively charged) disrupted the water structure similarly to low DOTAP concentrations, whereas SCN- and ibuprofen (both negatively charged) enhanced the water structure. These results suggest a direct correlation amongst the interfacial water structure, area per lipid, and surface charge density.

10.
J Phys Chem Lett ; 9(23): 6739-6743, 2018 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-30398354

RESUMO

Pure aqueous electrolyte solutions display a minimum in surface tension at concentrations of 2 ± 1 mM. This effect has been a source of controversy since it was first reported by Jones and Ray in the 1930s. The Jones-Ray effect has frequently been dismissed as an artifact linked to the presence of surface-active impurities. Herein we systematically consider the effect of surface-active impurities by purposely adding nanomolar concentrations of surfactants to dilute electrolyte solutions. Trace amounts of surfactant are indeed found to decrease the surface tension and influence the surface chemistry. However, surfactants can be removed by repeated aspiration and stirring cycles, which eventually deplete the surfactant from solution, creating a pristine surface. Upon following this cleaning procedure, a reduction in the surface tension by millimolar concentrations of salt is still observed. Consequently, we demonstrate that the Jones-Ray effect is not caused by surface-active impurities.

11.
Langmuir ; 34(36): 10782-10792, 2018 09 11.
Artigo em Inglês | MEDLINE | ID: mdl-30148644

RESUMO

Ibuprofen (IBU) interacts with phosphatidylcholine membranes in three distinct steps as a function of concentration. In a first step (<10 µM), IBU electrostatically adsorbs to the lipid headgroups and gradually decreases the interfacial potential. This first step helps to facilitate the second step (10-300 µM), in which hydrophobic insertion of the drug occurs. The second step disrupts the packing of the lipid acyl chains and expands the area per lipid. In a final step, above 300 µM IBU, the lipid membrane begins to solubilize, resulting in a detergent-like effect. The results described herein were obtained by a combination of fluorescence binding assays, vibrational sum frequency spectroscopy, and Langmuir monolayer compression experiments. By introducing trimethylammonium-propane, phosphatidylglycerol, and phosphatidylethanolamine lipids as well as cholesterol, we demonstrated that both the chemistry of the lipid headgroups and the packing of lipid acyl chains can substantially influence the interactions between IBU and the membranes. Moreover, different membrane chemistries can alter particular steps in the binding interaction.


Assuntos
Ibuprofeno/química , Bicamadas Lipídicas/química , Colesterol/química , Ácidos Graxos Monoinsaturados/química , Corantes Fluorescentes/química , Interações Hidrofóbicas e Hidrofílicas , Fosfatidiletanolaminas/química , Fosfatidilgliceróis/química , Compostos de Amônio Quaternário/química , Rodaminas/química , Eletricidade Estática
12.
Nat Commun ; 9(1): 3304, 2018 08 14.
Artigo em Inglês | MEDLINE | ID: mdl-30108220

RESUMO

The original version of this Article contained an error in the spelling of the author Woochul Song, which was incorrectly given as Woochul C. Song. This has been corrected in both the PDF and HTML versions of the Article.

13.
Nat Commun ; 9(1): 2294, 2018 06 12.
Artigo em Inglês | MEDLINE | ID: mdl-29895901

RESUMO

Synthetic polymer membranes, critical to diverse energy-efficient separations, are subject to permeability-selectivity trade-offs that decrease their overall efficacy. These trade-offs are due to structural variations (e.g., broad pore size distributions) in both nonporous membranes used for Angstrom-scale separations and porous membranes used for nano to micron-scale separations. Biological membranes utilize well-defined Angstrom-scale pores to provide exceptional transport properties and can be used as inspiration to overcome this trade-off. Here, we present a comprehensive demonstration of such a bioinspired approach based on pillar[5]arene artificial water channels, resulting in artificial water channel-based block copolymer membranes. These membranes have a sharp selectivity profile with a molecular weight cutoff of ~ 500 Da, a size range challenging to achieve with current membranes, while achieving a large improvement in permeability (~65 L m-2 h-1 bar-1 compared with 4-7 L m-2 h-1 bar-1) over similarly rated commercial membranes.


Assuntos
Membranas Artificiais , Simulação de Dinâmica Molecular , Polímeros/química , Água/química , Aquaporinas/química , Simulação por Computador , Detergentes/química , Bicamadas Lipídicas/química , Lipossomos/química , Microscopia Confocal , Microscopia Eletrônica de Transmissão , Peso Molecular , Permeabilidade , Porosidade , Sais/química
14.
Structure ; 25(12): 1875-1886.e7, 2017 12 05.
Artigo em Inglês | MEDLINE | ID: mdl-29211985

RESUMO

Some viruses use phosphatidylinositol phosphate (PIP) to mark membranes used for genome replication or virion assembly. PIP-binding motifs of cellular proteins do not exist in viral proteins. Molecular-docking simulations revealed a putative site of PIP binding to poliovirus (PV) 3C protein that was validated using nuclear magnetic resonance spectroscopy. The PIP-binding site was located on a highly dynamic α helix, which also functions in RNA binding. Broad PIP-binding activity was observed in solution using a fluorescence polarization assay or in the context of a lipid bilayer using an on-chip, fluorescence assay. All-atom molecular dynamics simulations of the 3C protein-membrane interface revealed PIP clustering and perhaps PIP-dependent conformations. PIP clustering was mediated by interaction with residues that interact with the RNA phosphodiester backbone. We conclude that 3C binding to membranes will be determined by PIP abundance. We suggest that the duality of function observed for 3C may extend to RNA-binding proteins of other viruses.


Assuntos
Cisteína Endopeptidases/química , Proteínas Virais/química , Sítios de Ligação , Cisteína Endopeptidases/metabolismo , Fosfatidilinositóis/química , Fosfatidilinositóis/metabolismo , Ligação Proteica , RNA/química , RNA/metabolismo , Proteínas Virais/metabolismo
15.
Nat Chem ; 10(1): 8-16, 2017 12 19.
Artigo em Inglês | MEDLINE | ID: mdl-29256514

RESUMO

On planet Earth, water is everywhere: the majority of the surface is covered with it; it is a key component of all life; its vapour and droplets fill the lower atmosphere; and even rocks contain it and undergo geomorphological changes because of it. A community of physical scientists largely drives studies of the chemistry of water and aqueous solutions, with expertise in biochemistry, spectroscopy and computer modelling. More recently, however, supramolecular chemists - with their expertise in macrocyclic synthesis and measuring supramolecular interactions - have renewed their interest in water-mediated non-covalent interactions. These two groups offer complementary expertise that, if harnessed, offer to accelerate our understanding of aqueous supramolecular chemistry and water writ large. This Review summarizes the state-of-the-art of the two fields, and highlights where there is latent chemical space for collaborative exploration by the two groups.

16.
Langmuir ; 33(46): 13423-13429, 2017 11 21.
Artigo em Inglês | MEDLINE | ID: mdl-29119796

RESUMO

Phosphatidylethanolamine (PE) is notoriously difficult to incorporate into model membrane systems, such as fluid supported lipid bilayers (SLBs), at high concentrations because of its intrinsic negative curvature. Using fluorescence-based techniques, we demonstrate that having fewer sites of unsaturation in the lipid tails leads to high-quality SLBs because these lipids help to minimize the curvature. Moreover, shorter saturated chains can help maintain the membranes in the fluid phase. Using these two guidelines, we find that up to 70 mol % PE can be incorporated into SLBs at room temperature and up to 90 mol % PE can be incorporated at 37 °C. Curiously, conditions under which three-dimensional tubules project outward from the planar surface as well as conditions under which domain formation occurs can be found. We have employed these model membrane systems to explore the ability of Ni2+ to bind to PE. It was found that this transition metal ion binds 1000-fold tighter to PE than to phosphatidylcholine lipids. In the future, this platform could be exploited to monitor the binding of other transition metal ions or the binding of antimicrobial peptides. It could also be employed to explore the physical properties of PE-containing membranes, such as phase domain behavior and intermolecular hydrogen bonding.

17.
J Vis Exp ; (125)2017 07 27.
Artigo em Inglês | MEDLINE | ID: mdl-28784961

RESUMO

Numerous cellular proteins interact with membrane surfaces to affect essential cellular processes. These interactions can be directed towards a specific lipid component within a membrane, as in the case of phosphoinositides (PIPs), to ensure specific subcellular localization and/or activation. PIPs and cellular PIP-binding domains have been studied extensively to better understand their role in cellular physiology. We applied a pH modulation assay on supported lipid bilayers (SLBs) as a tool to study protein-PIP interactions. In these studies, pH sensitive ortho-Sulforhodamine B conjugated phosphatidylethanolamine is used to detect protein-PIP interactions. Upon binding of a protein to a PIP-containing membrane surface, the interfacial potential is modulated (i.e. change in local pH), shifting the protonation state of the probe. A case study of the successful usage of the pH modulation assay is presented by using phospholipase C delta1 Pleckstrin Homology (PLC-δ1 PH) domain and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) interaction as an example. The apparent dissociation constant (Kd,app) for this interaction was 0.39 ± 0.05 µM, similar to Kd,app values obtained by others. As previously observed, the PLC-δ1 PH domain is PI(4,5)P2 specific, shows weaker binding towards phosphatidylinositol 4-phosphate, and no binding to pure phosphatidylcholine SLBs. The PIP-on-a-chip assay is advantageous over traditional PIP-binding assays, including but not limited to low sample volume and no ligand/receptor labeling requirements, the ability to test high- and low-affinity membrane interactions with both small and large molecules, and improved signal to noise ratio. Accordingly, the usage of the PIP-on-a-chip approach will facilitate the elucidation of mechanisms of a wide range of membrane interactions. Furthermore, this method could potentially be used in identifying therapeutics that modulate protein's capacity to interact with membranes.


Assuntos
Fosfatidilinositóis/metabolismo , Fosfolipase C delta/metabolismo , Humanos , Concentração de Íons de Hidrogênio , Cinética , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Fluidez de Membrana , Fosfatidilinositol 4,5-Difosfato/química , Fosfatidilinositol 4,5-Difosfato/metabolismo , Fosfatidilinositóis/química , Fosfolipase C delta/química , Análise Serial de Proteínas , Ligação Proteica , Domínios Proteicos , Lipossomas Unilamelares/química , Lipossomas Unilamelares/metabolismo , Gravação em Vídeo
18.
ACS Nano ; 11(7): 6594-6604, 2017 07 25.
Artigo em Inglês | MEDLINE | ID: mdl-28704035

RESUMO

Herein, we describe the development of oblique colloidal lithography (OCL) and establish a systematic patterning strategy for creating libraries of nanosized nonconcentric plasmonic structures. This strategy combines OCL, capillary force lithography, and several wet and ion etching steps. Hexagonal arrays of nonconcentric gold features were created on glass substrates with highly controllable geometric parameters. The size, geometry, and eccentricity of the gold features could be independently tuned by controlling the experimental conditions. Gaps within surface elements could be shrunk to as small as 30 nm, while the total patterned area was about l cm2. The goal was to devise a method that offers a high degree of control over the resolution and morphology of asymmetric structures without the need to resort to electron beam lithography. This technique also enabled the development of numerous surface patterns through the stepwise fabrication of separate elements. Complex features, including dots-surrounded nonconcentric targets, nonconcentric hexagram-disks, and nonconcentric annular aperture arrays, were demonstrated, and their optical properties were characterized. Indeed, spectroscopic studies and FDTD simulations demonstrated that Fano resonances could readily be generated by the nonconcentric gold features. Consequently, our patterning strategy should enable the high-throughput investigation of plasmonic coupling and Fano resonances as a function of the physical parameters of the elements within the nanopattern array.

19.
J Am Chem Soc ; 139(11): 4019-4024, 2017 03 22.
Artigo em Inglês | MEDLINE | ID: mdl-28177616

RESUMO

The orchestrated recognition of phosphoinositides and concomitant intracellular release of Ca2+ is pivotal to almost every aspect of cellular processes, including membrane homeostasis, cell division and growth, vesicle trafficking, as well as secretion. Although Ca2+ is known to directly impact phosphoinositide clustering, little is known about the molecular basis for this or its significance in cellular signaling. Here, we study the direct interaction of Ca2+ with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), the main lipid marker of the plasma membrane. Electrokinetic potential measurements of PI(4,5)P2 containing liposomes reveal that Ca2+ as well as Mg2+ reduce the zeta potential of liposomes to nearly background levels of pure phosphatidylcholine membranes. Strikingly, lipid recognition by the default PI(4,5)P2 lipid sensor, phospholipase C delta 1 pleckstrin homology domain (PLC δ1-PH), is completely inhibited in the presence of Ca2+, while Mg2+ has no effect with 100 nm liposomes and modest effect with giant unilamellar vesicles. Consistent with biochemical data, vibrational sum frequency spectroscopy and atomistic molecular dynamics simulations reveal how Ca2+ binding to the PI(4,5)P2 headgroup and carbonyl regions leads to confined lipid headgroup tilting and conformational rearrangements. We rationalize these findings by the ability of calcium to block a highly specific interaction between PLC δ1-PH and PI(4,5)P2, encoded within the conformational properties of the lipid itself. Our studies demonstrate the possibility that switchable phosphoinositide conformational states can serve as lipid recognition and controlled cell signaling mechanisms.


Assuntos
Cálcio/metabolismo , Simulação de Dinâmica Molecular , Fosfatidilinositol 4,5-Difosfato/metabolismo , Cálcio/química , Conformação Molecular , Fosfatidilinositol 4,5-Difosfato/química
20.
Proc Natl Acad Sci U S A ; 114(10): 2479-2484, 2017 03 07.
Artigo em Inglês | MEDLINE | ID: mdl-28228526

RESUMO

We report experimental and computational studies investigating the effects of three osmolytes, trimethylamine N-oxide (TMAO), betaine, and glycine, on the hydrophobic collapse of an elastin-like polypeptide (ELP). All three osmolytes stabilize collapsed conformations of the ELP and reduce the lower critical solution temperature (LSCT) linearly with osmolyte concentration. As expected from conventional preferential solvation arguments, betaine and glycine both increase the surface tension at the air-water interface. TMAO, however, reduces the surface tension. Atomically detailed molecular dynamics (MD) simulations suggest that TMAO also slightly accumulates at the polymer-water interface, whereas glycine and betaine are strongly depleted. To investigate alternative mechanisms for osmolyte effects, we performed FTIR experiments that characterized the impact of each cosolvent on the bulk water structure. These experiments showed that TMAO red-shifts the OH stretch of the IR spectrum via a mechanism that was very sensitive to the protonation state of the NO moiety. Glycine also caused a red shift in the OH stretch region, whereas betaine minimally impacted this region. Thus, the effects of osmolytes on the OH spectrum appear uncorrelated with their effects upon hydrophobic collapse. Similarly, MD simulations suggested that TMAO disrupts the water structure to the least extent, whereas glycine exerts the greatest influence on the water structure. These results suggest that TMAO stabilizes collapsed conformations via a mechanism that is distinct from glycine and betaine. In particular, we propose that TMAO stabilizes proteins by acting as a surfactant for the heterogeneous surfaces of folded proteins.


Assuntos
Betaína/química , Elastina/química , Glicina/química , Metilaminas/química , Peptídeos/química , Ar/análise , Interações Hidrofóbicas e Hidrofílicas , Simulação de Dinâmica Molecular , Pressão Osmótica , Dobramento de Proteína , Soluções , Tensão Superficial , Água/química
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