151
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Roldan N, Goormaghtigh E, Pérez-Gil J, Garcia-Alvarez B. Palmitoylation as a key factor to modulate SP-C–lipid interactions in lung surfactant membrane multilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:184-91. [DOI: 10.1016/j.bbamem.2014.10.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2014] [Revised: 09/16/2014] [Accepted: 10/01/2014] [Indexed: 11/24/2022]
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152
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Arai S, Lee CLK, Chang YT, Sato H, Sou K. Thermosensitive nanoplatforms for photothermal release of cargo from liposomes under intracellular temperature monitoring. RSC Adv 2015. [DOI: 10.1039/c5ra19729e] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Cargo release from thermosensitive liposomes by a near infrared laser was investigated under intracellular temperature monitoring.
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Affiliation(s)
- Satoshi Arai
- Waseda Bioscience Research Institute in Singapore (WABIOS)
- Singapore 138667
- Singapore
- Organization for University Research Initiatives
- Waseda University
| | - Chi-Lik Ken Lee
- Centre for Biomedical and Life Sciences
- Department for Technology
- Innovation and Enterprise (TIE)
- Singapore Polytechnic
- Singapore 139651
| | - Young-Tae Chang
- Department of Chemistry and NUS Medchem Program of the Life Sciences Institute
- National University of Singapore
- Singapore 117543
- Singapore
| | - Hirotaka Sato
- School of Mechanical and Aerospace Engineering
- Nanyang Technological University
- Singapore 637460
- Singapore
| | - Keitaro Sou
- Waseda Bioscience Research Institute in Singapore (WABIOS)
- Singapore 138667
- Singapore
- Organization for University Research Initiatives
- Waseda University
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153
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Taylor GJ, Sarles SA. Heating-enabled formation of droplet interface bilayers using Escherichia coli total lipid extract. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 31:325-37. [PMID: 25514167 DOI: 10.1021/la503471m] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Droplet interface bilayers (DIBs) serve as a convenient platform to study interactions between synthetic lipid membranes and proteins. However, a majority of DIBs have been assembled using a single lipid type, diphytanoylphosphatidylcholine (DPhPC). The work described herein establishes a new method to assemble DIBs using total lipid extract from Escherichia coli (eTLE); it is found that incubating oil-submerged aqueous droplets containing eTLE liposomes at a temperature above the gel-fluid phase transition temperature (Tg) promotes monolayer self-assembly that does not occur below Tg. Once monolayers are properly assembled via heating, droplets can be directly connected or cooled below Tg and then connected to initiate bilayer formation. This outcome contrasts immediate droplet coalescence observed upon contact between nonheated eTLE-infused droplets. Specific capacitance measurements confirm that the interface between droplets containing eTLE lipids is a lipid bilayer with thickness of 29.6 Å at 25 °C in hexadecane. We observe that bilayers formed from eTLE or DPhPC survive cooling and heating between 25 and 50 °C and demonstrate gigaohm (GΩ) membrane resistances at all temperatures tested. Additionally, we study the insertion of alamethicin peptides into both eTLE and DPhPC membranes to understand how lipid composition, temperature, and membrane phase influence ion channel formation. Like in DPhPC bilayers, alamethicin peptides in eTLE exhibit discrete, voltage-dependent gating characterized by multiple open channel conductance levels, though at significantly lower applied voltages. Cyclic voltammetry measurements of macroscopic channel currents confirm that the voltage-dependent conductance of alamethicin channels in eTLE bilayers occurs at lower voltages than in DPhPC bilayers at equivalent peptide concentrations. This result suggests that eTLE membranes, via composition, fluidity, or the presence of subdomains, offer an environment that enhances alamethicin insertion. For both membrane compositions, increasing temperature reduces the lifetimes of single channel gating events and increases the voltage required to cause an exponential increase in channel current. However, the fact that alamethicin insertion in eTLE exhibits significantly greater sensitivity to temperature changes through its Tg suggests that membrane phase plays an important role in channel formation. These effects are much less severe in DPhPC, where heating from 25 to 50 °C does not induce a phase change. The described technique for heating-assisted monolayer formation permits the use of other high transition temperature lipids in aqueous droplets for DIB formation, thereby increasing the types of lipids that can be considered for assembling model membranes.
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Affiliation(s)
- Graham J Taylor
- Department of Mechanical, Aerospace, and Biomedical Engineering, University of Tennessee , Knoxville, Tennessee 37996, United States
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154
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Meckes B, Ambrosi C, Barnard H, Arce FT, Sosinsky GE, Lal R. Atomic force microscopy shows connexin26 hemichannel clustering in purified membrane fragments. Biochemistry 2014; 53:7407-14. [PMID: 25365227 PMCID: PMC4255643 DOI: 10.1021/bi501265p] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
![]()
Connexin
proteins form hexameric assemblies known as hemichannels.
When docked to form gap junction (GJ) channels, hemichannels play
a critical role in cell–cell communication and cellular homeostasis,
but often are functional entities on their own in unapposed cell membranes.
Defects in the Connexin26 (Cx26) gene are the major cause of hereditary
deafness arising from dysfunctional hemichannels in the cochlea. Structural
studies of Cx26 hemichannels properly trafficked and inserted in plasma
membranes, including their clustering that forms a plaque-like feature
in whole gap junctions, are limited. We used atomic force microscopy
(AFM) to study the surface topography of Cx26 hemichannels using two
different membrane preparations. Rat Cx26 containing appended carboxy
terminal V5 and hexahistidine tags were expressed in baculovirus/Sf9
cell systems. The expressed Cx26 proteins form hemichannels in situ
in Sf9 cells that were then purified either as (1) Sf9 membrane fragments
containing Cx26 hemichannels or (2) solubilized hemichannels. The
latter were subsequently reconstituted in liposomes. AFM images of
purified membrane fragments showed clusters of protein macromolecular
structures in the membrane that at higher magnification corresponded
to Cx26 hemichannels. Hemichannels reconstituted into DOPC bilayers
displayed two populations of channel heights likely resulting from
differences in orientations of inserted hemichannels. Hemichannels
in the protein rich portions of purified membranes also showed a reduced
channel height above the bilayer compared to membranes with reconstituted
hemichannels perhaps due to reduced AFM probe access to the lipid
bilayer. These preparations of purified membranes enriched for connexin
hemichannels that have been properly trafficked and inserted in membranes
provide a platform for high-resolution AFM imaging of the structure,
interconnexon interactions, and cooperativity of properly trafficked
and inserted noncrystalline connexin hemichannels.
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Affiliation(s)
- Brian Meckes
- Department of Bioengineering, ‡National Center for Microscopy and Imaging Research, §Department of Aerospace and Mechanical Engineering, ∥Department of Neurosciences, and ⊥Materials Science Program, University of California San Diego , 9500 Gillman Drive, La Jolla, California 92093, United States
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155
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Ionic strength and composition govern the elasticity of biological membranes. A study of model DMPC bilayers by force- and transmission IR spectroscopy. Chem Phys Lipids 2014; 186:17-29. [PMID: 25447291 DOI: 10.1016/j.chemphyslip.2014.11.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 11/05/2014] [Accepted: 11/11/2014] [Indexed: 12/15/2022]
Abstract
Infrared (IR) spectroscopy was used to quantify the ion mixture effect of seawater (SW), particularly the contribution of Mg(2+) and Ca(2+) as dominant divalent cations, on the thermotropic phase behaviour of 1,2-dimyristoyl-sn-glycero-3-posphocholine (DMPC) bilayers. The changed character of the main transition at 24 °C from sharp to gradual in films and the 1 °C shift of the main transition temperature in dispersions reflect the interactions of lipid headgroups with the ions in SW. Force spectroscopy was used to quantify the nanomechanical hardness of a DMPC supported lipid bilayer (SLB). Considering the electrostatic and ion binding equilibrium contributions while systematically probing the SLB in various salt solutions, we showed that ionic strength had a decisive influence on its nanomechanics. The mechanical hardness of DMPC SLBs in the liquid crystalline phase linearly increases with the increasing fraction of all ion-bound lipids in a series of monovalent salt solutions. It also linearly increases in the gel phase but almost three times faster (the corresponding slopes are 4.9 nN/100 mM and 13.32 nN/100 mM, respectively). We also showed that in the presence of divalent ions (Ca(2+) and Mg(2+)) the bilayer mechanical hardness was unproportionally increased, and that was accompanied with the decrease of Na(+) ion and increase of Cl(-) ion bound lipids. The underlying process is a cooperative and competitive ion binding in both the gel and the liquid crystalline phase. Bilayer hardness thus turned out to be very sensitive to ionic strength as well as to ionic composition of the surrounding medium. In particular, the indicated correlation helped us to emphasize the colligative properties of SW as a naturally occurring complex ion mixture.
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156
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Aydin F, Ludford P, Dutt M. Phase segregation in bio-inspired multi-component vesicles encompassing double tail phospholipid species. SOFT MATTER 2014; 10:6096-6108. [PMID: 25008809 DOI: 10.1039/c4sm00998c] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Our aim is to investigate the phase segregation and the structure of multi-component bio-inspired phospholipid vesicles via dissipative particle dynamics. The chemical distinction in the phospholipid species arises due to different head and tail group moieties, and molecular stiffness of the hydrocarbon tails. The individual amphiphilic phospholipid molecular species are represented by a hydrophilic head group and two hydrophobic tails. The distinct chemical nature of the moieties is modeled effectively via soft repulsive interaction parameters, and the molecular rigidity is tuned via suitable three-body potential constants. We demonstrate the formation of a stable hybrid vesicle through the self-assembly of the amphiphilic phospholipid molecules in the presence of a hydrophilic solvent. We investigate and characterize the phase segregation and the structure of the binary vesicles for different phospholipid mixtures. Our results demonstrate macroscopic phase separation for phospholipid mixtures composed of species with different hydrocarbon tail groups. We also investigate the relationship between the phase segregation and thermodynamic variables such as interfacial line tension and surface tension, and obtain correspondence between existing theory and experiments, and our simulation results. We report variations in the molecular chain stiffness to have negligible contributions to the phase segregation in the mixed bilayer, and to demonstrate shape transformations of the hybrid vesicle. Our results can be used to design novel bio-inspired hybrid vehicles for potential applications in biomedicine, sensing, imaging and sustainability.
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Affiliation(s)
- Fikret Aydin
- Department of Chemical Engineering, Rutgers The State University of New Jersey, Piscataway, NJ 08854, USA.
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157
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Taylor RW, Benz F, Sigle DO, Bowman RW, Bao P, Roth JS, Heath GR, Evans SD, Baumberg JJ. Watching individual molecules flex within lipid membranes using SERS. Sci Rep 2014; 4:5940. [PMID: 25113088 PMCID: PMC4129422 DOI: 10.1038/srep05940] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Accepted: 07/16/2014] [Indexed: 11/17/2022] Open
Abstract
Interrogating individual molecules within bio-membranes is key to deepening our understanding of biological processes essential for life. Using Raman spectroscopy to map molecular vibrations is ideal to non-destructively ‘fingerprint’ biomolecules for dynamic information on their molecular structure, composition and conformation. Such tag-free tracking of molecules within lipid bio-membranes can directly connect structure and function. In this paper, stable co-assembly with gold nano-components in a ‘nanoparticle-on-mirror’ geometry strongly enhances the local optical field and reduces the volume probed to a few nm3, enabling repeated measurements for many tens of minutes on the same molecules. The intense gap plasmons are assembled around model bio-membranes providing molecular identification of the diffusing lipids. Our experiments clearly evidence measurement of individual lipids flexing through telltale rapid correlated vibrational shifts and intensity fluctuations in the Raman spectrum. These track molecules that undergo bending and conformational changes within the probe volume, through their interactions with the environment. This technique allows for in situ high-speed single-molecule investigations of the molecules embedded within lipid bio-membranes. It thus offers a new way to investigate the hidden dynamics of cell membranes important to a myriad of life processes.
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Affiliation(s)
- Richard W Taylor
- 1] NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, JJ Thompson Ave, University of Cambridge, Cambridge, CB3 0HE, UK [2]
| | - Felix Benz
- 1] NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, JJ Thompson Ave, University of Cambridge, Cambridge, CB3 0HE, UK [2]
| | - Daniel O Sigle
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, JJ Thompson Ave, University of Cambridge, Cambridge, CB3 0HE, UK
| | - Richard W Bowman
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, JJ Thompson Ave, University of Cambridge, Cambridge, CB3 0HE, UK
| | - Peng Bao
- Department of Physics, University of Leeds, Leeds, UK
| | | | | | | | - Jeremy J Baumberg
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, JJ Thompson Ave, University of Cambridge, Cambridge, CB3 0HE, UK
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158
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Ramkaran M, Badia A. Gel-to-Fluid Phase Transformations in Solid-Supported Phospholipid Bilayers Assembled by the Langmuir–Blodgett Technique: Effect of the Langmuir Monolayer Phase State and Molecular Density. J Phys Chem B 2014; 118:9708-21. [DOI: 10.1021/jp504092b] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Mohini Ramkaran
- Department of Chemistry,
FRQNT Centre for Self-Assembled Chemical Structures, Université de Montréal, C.P. 6128 succursale Centre-ville, Montréal, QC H3C 3J7, Canada
| | - Antonella Badia
- Department of Chemistry,
FRQNT Centre for Self-Assembled Chemical Structures, Université de Montréal, C.P. 6128 succursale Centre-ville, Montréal, QC H3C 3J7, Canada
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159
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160
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Aydin F, Dutt M. Bioinspired Vesicles Encompassing Two-Tail Phospholipids: Self-Assembly and Phase Segregation via Implicit Solvent Coarse-Grained Molecular Dynamics. J Phys Chem B 2014; 118:8614-23. [DOI: 10.1021/jp503376r] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Fikret Aydin
- Department
of Chemical and Biochemical Engineering, Rutgers The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Meenakshi Dutt
- Department
of Chemical and Biochemical Engineering, Rutgers The State University of New Jersey, Piscataway, New Jersey 08854, United States
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161
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Nojima Y, Iwata K. Viscosity heterogeneity inside lipid bilayers of single-component phosphatidylcholine liposomes observed with picosecond time-resolved fluorescence spectroscopy. J Phys Chem B 2014; 118:8631-41. [PMID: 24967901 DOI: 10.1021/jp503921e] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A number of biochemical reactions proceed inside biomembranes. Because the rate of a chemical reaction is influenced by chemical properties of the reaction field, it is important to examine the chemical properties inside the biomembranes, or lipid bilayer membranes, for understanding biochemical reactions. In this study, we estimate viscosity inside the lipid bilayers of liposomes with picosecond time-resolved fluorescence spectroscopy. trans-Stilbene is solubilized in the lipid bilayers formed by phosphatidylcholines, DSPC, DOPC, DPPC, DMPC, and DLPC, with 18, 18, 16, 14, and 12 carbon atoms in their alkyl chains, respectively, and egg-PC. Viscosity inside the lipid bilayer is estimated from the photoisomerization rate constant and from the rotational relaxation time of the first excited singlet state of trans-stilbene. The effect of the hydrocarbon chain length and temperature on viscosity is examined. The presence of two solvation environments within the lipid bilayer is indicated from the two independent estimations. One environment is 30 to 290 times more viscous than the other. Even single-component lipid bilayers are likely to have heterogeneous structures.
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Affiliation(s)
- Yuki Nojima
- Department of Chemistry, Faculty of Science, Gakushuin University , 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
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162
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Lü J, Yang J, Dong M, Sahin O. Nanomechanical spectroscopy of synthetic and biological membranes. NANOSCALE 2014; 6:7604-8. [PMID: 24895687 DOI: 10.1039/c3nr02643d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We report that atomic force microscopy based high-speed nanomechanical analysis can identify components of complex heterogeneous synthetic and biological membranes from the measured spectrum of nanomechanical properties. We have investigated phase separated ternary lipid bilayers and purple membranes of Halobacterium salinarum. The nanomechanical spectra recorded on these samples identify all membrane components, some of which are difficult to resolve in conventional phase images. This non-destructive approach can aid the design of synthetic lipid bilayers and studies lateral organization of complex heterogeneous cellular membranes.
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Affiliation(s)
- Junhong Lü
- The Rowland Institute at Harvard, Harvard University, Cambridge, MA, USA
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163
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Lind TK, Cárdenas M, Wacklin HP. Formation of Supported Lipid Bilayers by Vesicle Fusion: Effect of Deposition Temperature. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:7259-63. [PMID: 24932971 DOI: 10.1021/la500897x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Affiliation(s)
- Tania Kjellerup Lind
- Nano-Science
Center and Institute of Chemistry, Copenhagen University, Copenhagen, Denmark
- European Spallation
Source ESS AB, Lund, Sweden
| | - Marité Cárdenas
- Nano-Science
Center and Institute of Chemistry, Copenhagen University, Copenhagen, Denmark
- Malmoe University, Health & Society, 20506 Malmoe, Sweden
| | - Hanna Pauliina Wacklin
- Nano-Science
Center and Institute of Chemistry, Copenhagen University, Copenhagen, Denmark
- European Spallation
Source ESS AB, Lund, Sweden
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164
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GABAergic pharmacological activity of propofol related compounds as possible enhancers of general anesthetics and interaction with membranes. Cell Biochem Biophys 2014; 67:515-25. [PMID: 23456454 DOI: 10.1007/s12013-013-9537-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Phenol compounds, such as propofol and thymol, have been shown to act on the GABAA receptor through interaction with specific sites of this receptor. In addition, considering the high lipophilicity of phenols, it is possible that their pharmacological activity may also be the result of the interaction of phenol molecules with the surrounding lipid molecules, modulating the supramolecular organization of the receptor environment. Thus, in the present study, we study the pharmacological activity of some propofol- and thymol-related phenols on the native GABAA receptor using primary cultures of cortical neurons and investigate the effects of these compounds on the micro viscosity of artificial membranes by means of fluorescence anisotropy. The phenol compounds analyzed in this article are carvacrol, chlorothymol, and eugenol. All compounds were able to enhance the binding of [(3)H]flunitrazepam with EC50 values in the micromolar range and to increase the GABA-evoked Cl(-) influx in a concentration-dependent manner, both effects being inhibited by the competitive GABAA antagonist bicuculline. These results strongly suggest that the phenols studied are positive allosteric modulators of this receptor. Chlorothymol showed a bell-type effect, reducing its positive effect at concentrations >100 μM. The concentrations necessary to induce positive allosteric modulation of GABAA receptor were not cytotoxic. Although all compounds were able to decrease the micro viscosity of artificial membranes, chlorothymol displayed a larger effect which could explain its effects on [(3)H]flunitrazepam binding and on cell viability at high concentrations. Finally, it is suggested that these compounds may exert depressant activity on the central nervous system and potentiate the effects of general anesthetics.
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165
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Lei H, Zhou X, Wu H, Song Y, Hu J, Guo S, Zhang Y. Morphology change and detachment of lipid bilayers from the mica substrate driven by graphene oxide sheets. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:4678-4683. [PMID: 24738932 DOI: 10.1021/la500788z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Understanding the interaction between graphene oxide (GO) and a lipid membrane is significant for exploring the biocompatibility and cytotoxicity of GO, which is the basis for utilizing GO in the fields of biosensors, bioimaging, drug delivery, antibacterials, and so on. In this article, we monitored the dynamic process of the morphology change and detachment of lipid bilayers on mica substrates prompted by GO sheets by in situ atomic force microscope (AFM) imaging. It was found that the bare lipid bilayer dramatically expanded in height and would be unstable and detachable from the mica substrates as induced by GO. The detached lipid molecules were found to bind to the GO surface. The results also imply that GO is likely to influence the height and stability of the supported lipid bilayers (SLBs) by adsorbing metal ions such as calcium ions that were used to stabilize the bilayer structures on the mica substrate. These findings illustrate a complicated effect of GO on the SLBs and should be helpful in future applications of GO in biotechnology.
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Affiliation(s)
- Haozhi Lei
- Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai 201800, China
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166
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Zheng H, Jiménez-Flores R, Gragson D, Everett DW. Phospholipid Architecture of the Bovine Milk Fat Globule Membrane Using Giant Unilamellar Vesicles as a Model. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2014; 62:3236-3243. [PMID: 24641452 DOI: 10.1021/jf500093p] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Giant unilamellar vesicles (GUVs) were constructed using an electroformation technique to mimic the morphology of the native milk fat globule membrane (MFGM) for the purpose of structural investigation. Bovine milk derived phospholipids were selected to manufacture GUVs which were characterized by confocal laser scanning microscopy after fluorescent staining. Circular nonfluorescent dark regions were observed in a 3/7 (mol/mol) surface mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3 phosphoethanolamine. Linear shaped dark lipid domains were found in GUVs containing sphingomyelin (SM) in the absence of cholesterol. The dark regions were interpreted as a gel phase formed by a high gel-liquid phase transition temperature (Tm) of DPPC and SM. This study provides a strategy for investigating the lipid structural organization within the native MFGM using a model lipid bilayer system and reveals that a SM and cholesterol association network is not the only requirement for nonfluorescent lipid domain formation and that PE is preferably located in the inner leaflet of the phospholipid bilayer.
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Affiliation(s)
- Haotian Zheng
- Riddet Institute , Palmerston North, 4442 Manawatu, New Zealand
- Department of Food Science, University of Otago , Dunedin, 9054 Otago, New Zealand
- Dairy Products Technology Center, California Polytechnic State University , San Luis Obispo, 93407 California, United States
| | - Rafael Jiménez-Flores
- Dairy Products Technology Center, California Polytechnic State University , San Luis Obispo, 93407 California, United States
| | - Derek Gragson
- Department of Chemistry and Biochemistry, California Polytechnic State University , San Luis Obispo, 93407 California, United States
| | - David W Everett
- Riddet Institute , Palmerston North, 4442 Manawatu, New Zealand
- Department of Food Science, University of Otago , Dunedin, 9054 Otago, New Zealand
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167
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Sachan AK, Galla HJ. Understanding the mutual impact of interaction between hydrophobic nanoparticles and pulmonary surfactant monolayer. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2014; 10:1069-1075. [PMID: 24339125 DOI: 10.1002/smll.201300315] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 09/07/2013] [Indexed: 06/03/2023]
Abstract
Interaction between hydrophobic nanoparticles (NPs) and a pulmonary surfactant (PS) film leads to a shift in molecular packing of surfactant molecules in the PS film around the interacting NPs. The resultant structural arrangement of surfactants around the NPs may be a potential structural factor responsible for their high retention ability within the film. Moreover, during this interaction, surfactant molecules coat the NPs and change their surface properties.
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Affiliation(s)
- Amit K Sachan
- Institute of Biochemistry, Westfälische Wilhelms Universität, Wilhelm-Klemm-Str.2, Münster, 48149, Germany; Institute of Medical Physics and Biophysics, Westfälische Wilhelms Universität, Robert-Koch-Str. 31, Münster, 48149, Germany
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168
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Fox CB, Mulligan SK, Sung J, Dowling QM, Fung HWM, Vedvick TS, Coler RN. Cryogenic transmission electron microscopy of recombinant tuberculosis vaccine antigen with anionic liposomes reveals formation of flattened liposomes. Int J Nanomedicine 2014; 9:1367-77. [PMID: 24648734 PMCID: PMC3956628 DOI: 10.2147/ijn.s56582] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Development of lipid-based adjuvant formulations to enhance the immunogenicity of recombinant vaccine antigens is a focus of modern vaccine research. Characterizing interactions between vaccine antigens and formulation excipients is important for establishing compatibility between the different components and optimizing vaccine stability and potency. Cryogenic transmission electron microscopy (TEM) is a highly informative analytical technique that may elucidate various aspects of protein- and lipid-based structures, including morphology, size, shape, and phase structure, while avoiding artifacts associated with staining-based TEM. In this work, cryogenic TEM is employed to characterize a recombinant tuberculosis vaccine antigen, an anionic liposome formulation, and antigen–liposome interactions. By performing three-dimensional tomographic reconstruction analysis, the formation of a population of protein-containing flattened liposomes, not present in the control samples, was detected. It is shown that cryogenic TEM provides unique information regarding antigen–liposome interactions not detectable by light-scattering-based methods. Employing a suite of complementary analytical techniques is important to fully characterize interactions between vaccine components.
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Affiliation(s)
| | | | | | | | | | | | - Rhea N Coler
- Infectious Disease Research Institute, Seattle, WA, USA
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169
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Kong X, Qin S, Lu D, Liu Z. Surface tension effects on the phase transition of a DPPC bilayer with and without protein: a molecular dynamics simulation. Phys Chem Chem Phys 2014; 16:8434-40. [DOI: 10.1039/c3cp55524k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A coarse-grained molecular dynamics simulation was applied to illustrate the phase transition behavior of the pure DPPC bilayer and aquaporin-embedded DPPC bilayer under different surface tensions.
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Affiliation(s)
- Xian Kong
- Department of Chemical Engineering
- Tsinghua University
- Beijing, China
| | - Shanshan Qin
- Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education)
- Department of Chemistry
- Tsinghua University
- Beijing 100084, P. R. China
| | - Diannan Lu
- Department of Chemical Engineering
- Tsinghua University
- Beijing, China
| | - Zheng Liu
- Department of Chemical Engineering
- Tsinghua University
- Beijing, China
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170
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Nagaraj K, Sakthinathan S, Arunachalam S. Thermodynamics and kinetic investigation of electron transfer reactions of surfactant cobalt(iii) complexes containing diimine ligands with iron(ii) in the presence of liposome vesicles and amphiphilic salt media. RSC Adv 2014. [DOI: 10.1039/c4ra07404a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The kinetics of reductions of surfactant cobalt(iii) complexes by iron(ii) in liposome vesicles (DPPC) and amphiphilic salt ((BMIM)Br) were studied at different temperatures by UV-Vis absorption spectroscopy method under pseudo first order conditions using an excess of the reductant.
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Affiliation(s)
- Karuppiah Nagaraj
- School of Chemistry
- Bharathidasan University
- Tiruchirapalli 620024, India
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171
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Fraňová MD, Repáková J, Holopainen JM, Vattulainen I. How to link pyrene to its host lipid to minimize the extent of membrane perturbations and to optimize pyrene dimer formation. Chem Phys Lipids 2014; 177:19-25. [DOI: 10.1016/j.chemphyslip.2013.10.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Revised: 10/08/2013] [Accepted: 10/11/2013] [Indexed: 11/30/2022]
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172
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Wang J, Liu KW, Segatori L, Biswal SL. Lipid Bilayer Phase Transformations Detected Using Microcantilevers. J Phys Chem B 2013; 118:171-8. [DOI: 10.1021/jp4095112] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jinghui Wang
- Department of Chemical and
Biomolecular Engineering, Rice University, Houston, Texas 77005, United States
| | - Kai-Wei Liu
- Department of Chemical and
Biomolecular Engineering, Rice University, Houston, Texas 77005, United States
| | - Laura Segatori
- Department of Chemical and
Biomolecular Engineering, Rice University, Houston, Texas 77005, United States
| | - Sibani Lisa Biswal
- Department of Chemical and
Biomolecular Engineering, Rice University, Houston, Texas 77005, United States
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173
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Mishra D, Das S, Krishnamurthy S, Pal S. Understanding the orientation of water molecules around the phosphate and attached functional groups in a phospholipid molecule: a DFT-based study. MOLECULAR SIMULATION 2013. [DOI: 10.1080/08927022.2013.783701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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174
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Fen LB, Chen S, Kyo Y, Herpoldt KL, Terrill NJ, Dunlop IE, McPhail DS, Shaffer MS, Schwander S, Gow A, Zhang J(J, Chung KF, Tetley TD, Porter AE, Ryan MP. The stability of silver nanoparticles in a model of pulmonary surfactant. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:11232-40. [PMID: 23988335 PMCID: PMC3990461 DOI: 10.1021/es403377p] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The growing use of silver nanoparticles (AgNPs) in consumer products has raised concerns about their potential impact on the environment and human health. Whether AgNPs dissolve and release Ag(+) ions, or coarsen to form large aggregates, is critical in determining their potential toxicity. In this work, the stability of AgNPs in dipalmitoylphosphatidylcholine (DPPC), the major component of pulmonary surfactant, was investigated as a function of pH. Spherical, citrate-capped AgNPs with average diameters of 14 ± 1.6 nm (n = 200) were prepared by a chemical bath reduction. The kinetics of Ag(+) ion release was strongly pH-dependent. After 14 days of incubation in sodium perchlorate (NaClO4) or perchloric acid (HClO4) solutions, the total fraction of AgNPs dissolved varied from ∼10% at pH 3, to ∼2% at pH 5, with negligible dissolution at pH 7. A decrease in pH from 7 to 3 also promoted particle aggregation and coarsening. DPPC (100 mg·L(-1)) delayed the release of Ag(+) ions, but did not significantly alter the total amount of Ag(+) released after two weeks. In addition, DPPC improved the dispersion of the AgNPs and inhibited aggregation and coarsening. TEM images revealed that the AgNPs were coated with a DPPC layer serving as a semipermeable layer. Hence, lung lining fluid, particularly DPPC, can modify the aggregation state and kinetics of Ag(+) ion release of inhaled AgNPs in the lung. These observations have important implications for predicting the potential reactivity of AgNPs in the lung and the environment.
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Affiliation(s)
- Leo Bey Fen
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
- Department of Mechanical Engineering, Faculty of Engineering Building, University of Malaya, Kuala Lumpur 50603, MALAYSIA
| | - Shu Chen
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - Yoshihiko Kyo
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - Karla-Luise Herpoldt
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - Nicholas J. Terrill
- Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom
| | - Iain E. Dunlop
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - David S. McPhail
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - Milo S. Shaffer
- Department of Chemistry and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - Stephan Schwander
- Department of Environmental and Occupational Health, University of Medicine and Dentistry (UMDNJ) School of Public Health, New Jersey, USA
| | - Andrew Gow
- Department of Pharmacology and Toxicology at Rutgers University, Piscataway, NJ, USA
| | - Junfeng (Jim) Zhang
- Department of Preventive Medicine, Keck School of Medicine, University of Southern California, USA
| | - Kian Fan Chung
- National Heart and Lung Institute, Imperial College London, UK
| | | | - Alexandra E. Porter
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
- Corresponding Authors: ; phone: (+44)2075946755; fax: (+44)2075945017. ; phone: (+44)2075949691; fax: (+44)2075945017
| | - Mary P. Ryan
- Department of Materials and London Centre for Nanotechnology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
- Corresponding Authors: ; phone: (+44)2075946755; fax: (+44)2075945017. ; phone: (+44)2075949691; fax: (+44)2075945017
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175
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Pähler G, Panse C, Diederichsen U, Janshoff A. Coiled-coil formation on lipid bilayers--implications for docking and fusion efficiency. Biophys J 2013; 103:2295-303. [PMID: 23283228 DOI: 10.1016/j.bpj.2012.08.053] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 07/31/2012] [Accepted: 08/15/2012] [Indexed: 11/26/2022] Open
Abstract
Coiled-coil formation of four different oligopeptides was characterized in solution, on hydrogels, and on membranes by employing circular dichroism spectroscopy, surface plasmon resonance spectroscopy, attenuated total reflection infrared spectroscopy, and ellipsometry. Peptide sequences rich in either glutamic acid (E: E3Cys, i-E3Cys) or lysine (K: K3Cys, i-K3Cys) were used to represent minimal mimics of eukaryotic SNARE motifs. Half of the peptides were synthesized in reverse sequence, so that parallel and antiparallel heptad coiled-coil structures were formed. Either E-peptides or K-peptides were attached covalently to phospholipid anchors via maleimide chemistry, and served as receptors for the recognition of the corresponding binding partners added to solution. Attenuated total reflection infrared spectroscopy of single bilayers confirmed the formation of coiled-coil complexes at the membrane interface. Coiled-coil formation in solution, as compared with association at the membrane surface, displays considerably larger binding constants that are largely attributed to loss of translational entropy at the interface. Finally, the fusogenicity of the various coiled-coil motifs was explored, and the results provide clear evidence that hemifusion followed by full fusion requires a parallel orientation of α-helices, whereas antiparallel oriented coiled-coil motifs display only docking.
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Affiliation(s)
- Gesa Pähler
- Institute of Physical Chemistry, Georg August University, Göttingen, Germany
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176
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Sterling SM, Allgeyer ES, Fick J, Prudovsky I, Mason MD, Neivandt DJ. Phospholipid diffusion coefficients of cushioned model membranes determined via z-scan fluorescence correlation spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:7966-74. [PMID: 23705855 PMCID: PMC3758428 DOI: 10.1021/la400768s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Model cellular membranes enable the study of biological processes in a controlled environment and reduce the traditional challenges associated with live or fixed cell studies. However, model membrane systems based on the air/water or oil/solution interface do not allow for incorporation of transmembrane proteins or for the study of protein transport mechanisms. Conversely, a phospholipid bilayer deposited via the Langmuir-Blodgett/Langmuir-Schaefer method on a hydrogel layer is potentially an effective mimic of the cross section of a biological membrane and facilitates both protein incorporation and transport studies. Prior to application, however, such membranes must be fully characterized, particularly with respect to the phospholipid bilayer phase transition temperature. Here we present a detailed characterization of the phase transition temperature of the inner and outer leaflets of a chitosan supported model membrane system. Specifically, the lateral diffusion coefficient of each individual leaflet has been determined as a function of temperature. Measurements were performed utilizing z-scan fluorescence correlation spectroscopy (FCS), a technique that yields calibration-free diffusion information. Analysis via the method of Wawrezinieck and co-workers revealed that phospholipid diffusion changes from raftlike to free diffusion as the temperature is increased-an insight into the dynamic behavior of hydrogel supported membranes not previously reported.
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Affiliation(s)
- Sarah M. Sterling
- Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469
- Graduate School of Biomedical Sciences, University of Maine, Orono, Maine 04469
| | - Edward S. Allgeyer
- Department of Physics and Astronomy, University of Maine, Orono, Maine 04469
| | - Jörg Fick
- Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469
| | - Igor Prudovsky
- Graduate School of Biomedical Sciences, University of Maine, Orono, Maine 04469
- Maine Medical Center Research Institute, Scarborough, ME 04074
- Institute for Molecular Biophysics, Orono, Maine 04469
| | - Michael D. Mason
- Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469
- Institute for Molecular Biophysics, Orono, Maine 04469
| | - David J. Neivandt
- Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469
- Graduate School of Biomedical Sciences, University of Maine, Orono, Maine 04469
- Institute for Molecular Biophysics, Orono, Maine 04469
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177
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Hoyo J, Guaus E, Oncins G, Torrent-Burgués J, Sanz F. Incorporation of ubiquinone in supported lipid bilayers on ITO. J Phys Chem B 2013; 117:7498-506. [PMID: 23725098 DOI: 10.1021/jp4004517] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Ubiquinone (UQ) is one of the main electron and proton shuttle molecules in biological systems, and dipalmitoylphosphatidylcholine (DPPC) is one of the most used model lipids. Supported planar bilayers (SPBs) are extensively accepted as biological model membranes. In this study, SPBs have been deposited on ITO, which is a semiconductor with good electrical and optical features. Specifically, topographic atomic force microscopy (AFM) images and force curves have been performed on SPBs with several DPPC:UQ ratios to study the location and the interaction of UQ in the SPB. Additionally, cyclic voltammetry has been used to understand the electrochemical behavior of DPPC:UQ SPBs. Obtained results show that, in our case, UQ is placed in two main different positions in SPBs. First, between the DPPC hydrophobic chains, fact that originates a decrease in the breakthrough force of the bilayer, and the second between the two leaflets that form the SPBs. This second position occurs when increasing the UQ content, fact that eventually forms UQ aggregates at high concentrations. The formation of aggregates produces an expansion of the SPB average height and a bimodal distribution of the breakthrough force. The voltammetric response of UQ depends on its position on the bilayer.
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Affiliation(s)
- Javier Hoyo
- Universitat Politècnica de Catalunya, Dpt. Enginyeria Química, 08222 Terrassa (Barcelona), Spain
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178
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Nanoscale measurement of the dielectric constant of supported lipid bilayers in aqueous solutions with electrostatic force microscopy. Biophys J 2013; 104:1257-62. [PMID: 23528085 DOI: 10.1016/j.bpj.2013.02.011] [Citation(s) in RCA: 111] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Revised: 01/23/2013] [Accepted: 02/11/2013] [Indexed: 12/31/2022] Open
Abstract
We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization forces which were measured using an electrostatic force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of ε(r) ~ 3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (ε(r) ~ 2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane electrostatics and other bioelectric phenomena.
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179
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Preparation of DOPC and DPPC Supported Planar Lipid Bilayers for Atomic Force Microscopy and Atomic Force Spectroscopy. Int J Mol Sci 2013; 14:3514-39. [PMID: 23389046 PMCID: PMC3588056 DOI: 10.3390/ijms14023514] [Citation(s) in RCA: 152] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Revised: 01/29/2013] [Accepted: 02/01/2013] [Indexed: 11/16/2022] Open
Abstract
Cell membranes are typically very complex, consisting of a multitude of different lipids and proteins. Supported lipid bilayers are widely used as model systems to study biological membranes. Atomic force microscopy and force spectroscopy techniques are nanoscale methods that are successfully used to study supported lipid bilayers. These methods, especially force spectroscopy, require the reliable preparation of supported lipid bilayers with extended coverage. The unreliability and a lack of a complete understanding of the vesicle fusion process though have held back progress in this promising field. We document here robust protocols for the formation of fluid phase DOPC and gel phase DPPC bilayers on mica. Insights into the most crucial experimental parameters and a comparison between DOPC and DPPC preparation are presented. Finally, we demonstrate force spectroscopy measurements on DOPC surfaces and measure rupture forces and bilayer depths that agree well with X-ray diffraction data. We also believe our approach to decomposing the force-distance curves into depth sub-components provides a more reliable method for characterising the depth of fluid phase lipid bilayers, particularly in comparison with typical image analysis approaches.
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180
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Wu H, Yu L, Tong Y, Ge A, Yau S, Osawa M, Ye S. Enzyme-catalyzed hydrolysis of the supported phospholipid bilayers studied by atomic force microscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:642-51. [DOI: 10.1016/j.bbamem.2012.09.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 09/06/2012] [Accepted: 09/07/2012] [Indexed: 01/17/2023]
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181
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Khelashvili G, Harries D. How Cholesterol Tilt Modulates the Mechanical Properties of Saturated and Unsaturated Lipid Membranes. J Phys Chem B 2013; 117:2411-21. [DOI: 10.1021/jp3122006] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York,
New York 10065, United States
| | - Daniel Harries
- Institute of Chemistry and the Fritz Haber Research Center, The Hebrew University of Jerusalem,
Jerusalem 91904, Israel
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182
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183
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Alessandrini A, Seeger HM, Caramaschi T, Facci P. Dynamic force spectroscopy on supported lipid bilayers: effect of temperature and sample preparation. Biophys J 2012; 103:38-47. [PMID: 22828330 DOI: 10.1016/j.bpj.2012.05.039] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 05/16/2012] [Accepted: 05/24/2012] [Indexed: 11/29/2022] Open
Abstract
Biological membranes are constantly exposed to forces. The stress-strain relation in membranes determines the behavior of many integral membrane proteins or other membrane related-proteins that show a mechanosensitive behavior. Here, we studied by force spectroscopy the behavior of supported lipid bilayers (SLBs) subjected to forces perpendicular to their plane. We measured the lipid bilayer mechanical properties and the force required for the punch-through event characteristic of atomic force spectroscopy on SLBs as a function of the interleaflet coupling. We found that for an uncoupled bilayer, the overall tip penetration occurs sequentially through the two leaflets, giving rise to two penetration events. In the case of a bilayer with coupled leaflets, penetration of the atomic force microscope tip always occurred in a single step. Considering the dependence of the jump-through force value on the tip speed, we also studied the process in the context of dynamic force spectroscopy (DFS). We performed DFS experiments by changing the temperature and cantilever spring constant, and analyzed the results in the context of the developed theories for DFS. We found that experiments performed at different temperatures and with different cantilever spring constants enabled a more effective comparison of experimental data with theory in comparison with previously published data.
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Affiliation(s)
- Andrea Alessandrini
- Centro S3, CNR-Istituto Nanoscienze, University of Modena and Reggio Emilia, Modena, Italy.
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184
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Picas L, Milhiet PE, Hernández-Borrell J. Atomic force microscopy: a versatile tool to probe the physical and chemical properties of supported membranes at the nanoscale. Chem Phys Lipids 2012. [PMID: 23194897 DOI: 10.1016/j.chemphyslip.2012.10.005] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Atomic force microscopy (AFM) was developed in the 1980s following the invention of its precursor, scanning tunneling microscopy (STM), earlier in the decade. Several modes of operation have evolved, demonstrating the extreme versatility of this method for measuring the physicochemical properties of samples at the nanoscopic scale. AFM has proved an invaluable technique for visualizing the topographic characteristics of phospholipid monolayers and bilayers, such as roughness, height or laterally segregated domains. Implemented modes such as phase imaging have also provided criteria for discriminating the viscoelastic properties of different supported lipid bilayer (SLB) regions. In this review, we focus on the AFM force spectroscopy (FS) mode, which enables determination of the nanomechanical properties of membrane models. The interpretation of force curves is presented, together with newly emerging techniques that provide complementary information on physicochemical properties that may contribute to our understanding of the structure and function of biomembranes. Since AFM is an imaging technique, some basic indications on how real-time AFM imaging is evolving are also presented at the end of this paper.
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Affiliation(s)
- Laura Picas
- Institut Curie, CNRS UMR 144, 26 rue d'Ulm, 75248 Paris, France
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185
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Kamiński DM, Matwijczuk A, Pociecha D, Górecka E, Niewiadomy A, Dmowska M, Gagoś M. Effect of 2-(4-fluorophenylamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole on the molecular organisation and structural properties of the DPPC lipid multibilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:2850-9. [DOI: 10.1016/j.bbamem.2012.07.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 07/17/2012] [Accepted: 07/18/2012] [Indexed: 01/12/2023]
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186
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The molecular organization of prenylated flavonoid xanthohumol in DPPC multibilayers: X-ray diffraction and FTIR spectroscopic studies. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:213-22. [PMID: 23085000 DOI: 10.1016/j.bbamem.2012.10.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2012] [Revised: 10/03/2012] [Accepted: 10/11/2012] [Indexed: 11/22/2022]
Abstract
Xanthohumol (XN) is the major prenylated flavonoid found in hop resin. It has attracted considerable attention in recent years due to its wide spectrum of biological activities and the beneficial effect on human health. Since lipid membrane is first target for biologically active compounds, we decided to investigate the influence of XN on the dipalmitoylphosphatidylcholine (DPPC) multibilayers. Interactions of XN with DPPC were investigated as a function of temperature and its concentration by using X-ray diffraction and the ATR-FTIR spectroscopy techniques. The aim of understanding the mechanisms of molecular interactions between XN and DPPC was to indicate the localization of the XN with respect to the membrane and the type of interaction with phospholipids. The results revealed that XN changes the physical properties of the DPPC multibilayers in the form of dry film. A new complex formation between XN and DPPC is reported. The detailed analysis of refraction effect indicates the changes in electron density ratio between hydrophobic and hydrophilic zones of lipid at phase transition. This is in compliance with reported changes in FTIR spectra where at pretransition XN moves from interface region between polar heads to the neighborhood of phosphate groups.
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187
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Dindia L, Murray J, Faught E, Davis TL, Leonenko Z, Vijayan MM. Novel nongenomic signaling by glucocorticoid may involve changes to liver membrane order in rainbow trout. PLoS One 2012; 7:e46859. [PMID: 23056491 PMCID: PMC3466178 DOI: 10.1371/journal.pone.0046859] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Accepted: 09/06/2012] [Indexed: 11/21/2022] Open
Abstract
Stress-induced glucocorticoid elevation is a highly conserved response among vertebrates. This facilitates stress adaptation and the mode of action involves activation of the intracellular glucocorticoid receptor leading to the modulation of target gene expression. However, this genomic effect is slow acting and, therefore, a role for glucocorticoid in the rapid response to stress is unclear. Here we show that stress levels of cortisol, the primary glucocorticoid in teleosts, rapidly fluidizes rainbow trout (Oncorhynchus mykiss) liver plasma membranes in vitro. This involved incorporation of the steroid into the lipid domains, as cortisol coupled to a membrane impermeable peptide moiety, did not affect membrane order. Studies confirmed that cortisol, but not sex steroids, increases liver plasma membrane fluidity. Atomic force microscopy revealed cortisol-mediated changes to membrane surface topography and viscoelasticity confirming changes to membrane order. Treating trout hepatocytes with stress levels of cortisol led to the modulation of cell signaling pathways, including the phosphorylation status of putative PKA, PKC and AKT substrate proteins within 10 minutes. The phosphorylation by protein kinases in the presence of cortisol was consistent with that seen with benzyl alcohol, a known membrane fluidizer. Our results suggest that biophysical changes to plasma membrane properties, triggered by stressor-induced glucocorticoid elevation, act as a nonspecific stress response and may rapidly modulate acute stress-signaling pathways.
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Affiliation(s)
- Laura Dindia
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Josh Murray
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Erin Faught
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Tracy L. Davis
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - Zoya Leonenko
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
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188
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Tanwir K, Shahid MN, Thomas A, Tsoukanova V. Coexisting phases in PEGylated phosphocholine membranes: a model study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:14000-14009. [PMID: 22954402 DOI: 10.1021/la302156x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Understanding the phase behavior of PEGylated phosphocholine membranes is becoming increasingly important in many biomedical applications. Here, we used binary mixtures of phosphocholines and PEG-phospholipids in monolayers on phosphate buffered saline as ideal models of PEGylated phosphocholine membranes. Several phase states and transitions between homogeneously mixed and completely immiscible phases have been visualized in these mixtures by epifluorescence microscopy, which is neither predicted nor easily explained by the existing interpretive schemes. The results of our study suggest that the phase state of PEGylated phosphocholine membranes may drastically vary depending on factors such as aliphatic chain length on phosphocholines and PEG-phospholipids, PEG content, and temperature. These findings are summarized in phase drawings and diagrams to demonstrate a striking variety of possible phases. The diagrams can also be instrumental in predicting the phase state of PEGylated phosphocholine membranes, in particular under physiological conditions.
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Affiliation(s)
- Kanwal Tanwir
- Department of Chemistry, York University, Toronto, ON, Canada
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189
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Vankemmelbeke M, O′Shea P, James R, Penfold CN. Interaction of nuclease colicins with membranes: insertion depth correlates with bilayer perturbation. PLoS One 2012; 7:e46656. [PMID: 23029560 PMCID: PMC3460906 DOI: 10.1371/journal.pone.0046656] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Accepted: 09/05/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Protein transport across cellular membranes is an important aspect of toxin biology. Escherichia coli cell killing by nuclease colicins occurs through DNA (DNases) or RNA (RNases) hydrolysis and to this end their cytotoxic domains require transportation across two sets of membranes. In order to begin to unravel the molecular mechanisms underlying the membrane translocation of colicin nuclease domains, we have analysed the membrane association of four DNase domains (E9, a charge reduction E9 mutant, E8, and E7) and one ribosomal RNase domain (E3) using a biomembrane model system. PRINCIPAL RESULTS We demonstrate, through the use of large unilamellar vesicles composed of synthetic and E. coli lipids and a membrane surface potential sensor, that the colicin nuclease domains bind anionic membranes only, with micromolar affinity and via a cooperative binding mechanism. The evaluation of the nuclease bilayer insertion depth, through a fluorescence quenching analysis using brominated lipids, indicates that the nucleases locate to differential regions in the bilayer. Colicin DNases target the interfacial region of the lipid bilayer, with the DNase E7 showing the deepest insertion, whereas the ribosomal RNase E3 penetrates into the hydrophobic core region of the bilayer. Furthermore, the membrane association of the DNase E7 and the ribosomal RNase E3 induces vesicle aggregation, lipid mixing and content leakage to a much larger extent than that of the other DNases analysed. CONCLUSIONS/SIGNIFICANCE Our results show, for the first time, that after the initial electrostatically driven membrane association, the pleiotropic membrane effects induced by colicin nuclease domains relate to their bilayer insertion depth and may be linked to their in vivo membrane translocation.
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Affiliation(s)
- Mireille Vankemmelbeke
- School of Molecular Medical Sciences, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, United Kingdom
- * E-mail:
| | - Paul O′Shea
- School of Biology, University of Nottingham, Nottingham, United Kingdom
| | - Richard James
- School of Molecular Medical Sciences, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Christopher N. Penfold
- School of Molecular Medical Sciences, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, United Kingdom
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190
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Moleiro LH, López-Montero I, Márquez I, Moreno S, Vélez M, Carrascosa JL, Monroy F. Efficient orthogonal integration of the bacteriophage ϕ29 DNA-portal connector protein in engineered lipid bilayers. ACS Synth Biol 2012; 1:414-24. [PMID: 23651339 DOI: 10.1021/sb3000063] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The portal connector of bacteriophage viruses constitutes a robust molecular machine for DNA translocation. In this paper we propose an optimized reconstitution method for efficient orthogonal integration of native viral connectors into lipid bilayers, particularly of giant unilamellar vesicles. Our nanoengineering plan considers the hydrophilic connector protein of the bacteriophage virus ϕ29 integrated into a specifically engineered bilayer made of "hydrophylized" lipids. From the precise knowledge of the connector structure, the membrane chemistry was designed by tuning reactivity in the bilayer using specific functional lipids. We show details on the reconstitution methods and experimental evidence about the integration of the portal protein in the engineered membrane. The proposed route provides an efficient method for orthogonal integration of native viral connectors into lipid bilayers in conditions adequate for functional DNA translocation. This concept could be potentially exploited in advanced nanotechnological realizations, particularly for the integration of these powerful machines into giant lipid vesicles with the aim of building a cargo-device useful for gene delivery applications.
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Affiliation(s)
- Lara H. Moleiro
- Departamento de Química
Física I, Universidad Complutense, 28040 Madrid, Spain
| | - Iván López-Montero
- Departamento de Química
Física I, Universidad Complutense, 28040 Madrid, Spain
| | - Ileana Márquez
- Instituto de Catálisis
y Petroleoquímica, CSIC, Marie Curie
2, Cantoblanco, 28049 Madrid, Spain
| | - Sonia Moreno
- Centro Nacional de Biotecnología, CSIC, c/Darwin 3, Cantoblanco, 28049 Madrid, Spain
| | - Marisela Vélez
- Instituto de Catálisis
y Petroleoquímica, CSIC, Marie Curie
2, Cantoblanco, 28049 Madrid, Spain
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia),
Cantoblanco, 28049 Madrid, Spain
| | - José L. Carrascosa
- Centro Nacional de Biotecnología, CSIC, c/Darwin 3, Cantoblanco, 28049 Madrid, Spain
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia),
Cantoblanco, 28049 Madrid, Spain
| | - Francisco Monroy
- Departamento de Química
Física I, Universidad Complutense, 28040 Madrid, Spain
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191
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Morandat S, Azouzi S, Beauvais E, Mastouri A, El Kirat K. Atomic force microscopy of model lipid membranes. Anal Bioanal Chem 2012; 405:1445-61. [DOI: 10.1007/s00216-012-6383-y] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2012] [Revised: 08/02/2012] [Accepted: 08/24/2012] [Indexed: 10/27/2022]
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192
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Redondo-Morata L, Giannotti MI, Sanz F. Influence of cholesterol on the phase transition of lipid bilayers: a temperature-controlled force spectroscopy study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:12851-12860. [PMID: 22873775 DOI: 10.1021/la302620t] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Cholesterol (Chol) plays the essential function of regulating the physical properties of the cell membrane by controlling the lipid organization and phase behavior and, thus, managing the membrane fluidity and its mechanical strength. Here, we explore the model system DPPC:Chol by means of temperature-controlled atomic force microscopy (AFM) imaging and AFM-based force spectroscopy (AFM-FS) to assess the influence of Chol on the membrane ordering and stability. We analyze the system in a representative range of compositions up to 50 mol % Chol studying the phase evolution upon temperature increase (from room temperature to temperatures high above the T(m) of the DPPC bilayer) and the corresponding (nano)mechanical stability. By this means, we correlate the mechanical behavior and composition with the lateral order of each phase present in the bilayers. We prove that low Chol contents lead to a phase-segregated system, whereas high contents of Chol can give a homogeneous bilayer. In both cases, Chol enhances the mechanical stability of the membrane, and an extraordinarily stable system is observed for equimolar fractions (50 mol % Chol). In addition, even when no thermal transition is detected by the traditional bulk analysis techniques for liposomes with high Chol content (40 and 50 mol %), we demonstrate that temperature-controlled AFM-FS is capable of identifying a thermal transition for the supported lipid bilayers. Finally, our results validate the AFM-FS technique as an ideal platform to differentiate phase coexistence and transitions in lipid bilayers and bridge the gap between the results obtained by traditional methods for bulk analysis, the theoretical predictions, and the behavior of these systems at the nanoscale.
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Affiliation(s)
- Lorena Redondo-Morata
- Institute for Bioengineering of Catalonia (IBEC), Baldiri i Reixac 15-21, 08028, Barcelona, Spain
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193
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Iordanov I, Renault M, Réat V, Bosshart PD, Engel A, Saurel O, Milon A. Dynamics of Klebsiella pneumoniae OmpA transmembrane domain: The four extracellular loops display restricted motion behavior in micelles and in lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:2344-53. [DOI: 10.1016/j.bbamem.2012.05.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 05/02/2012] [Accepted: 05/03/2012] [Indexed: 10/28/2022]
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194
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Gunnarsson A, Bally M, Jönsson P, Médard N, Höök F. Time-resolved surface-enhanced ellipsometric contrast imaging for label-free analysis of biomolecular recognition reactions on glycolipid domains. Anal Chem 2012; 84:6538-45. [PMID: 22803821 DOI: 10.1021/ac300832k] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
We have applied surface-enhanced ellipsometry contrast (SEEC) imaging for time-resolved label-free visualization of biomolecular recognition events on spatially heterogeneous supported lipid bilayers (SLB). Using a conventional inverted microscope equipped with total internal reflection (TIR) illumination, biomolecular binding events were monitored with a lateral resolution near the optical diffraction limit at an acquisition rate of ~1 Hz with a sensitivity in terms of surface coverage of ~1 ng/cm(2). Despite the significant improvement in spatial resolution compared to alternative label-free surface-based imaging technologies, the sensitivity remains competitive with surface plasmon resonance (SPR) imaging and imaging ellipsometry. The potential of the technique to discriminate local differences in protein binding kinetics was demonstrated by time-resolved imaging of anti-GalCer antibodies binding to phase-separated lipid bilayers consisting of phosphatidylcholine (POPC) and galactosylceramide (GalCer). A higher antibody binding capacity was observed on the GalCer-diluted fluid region in comparison to the GalCer-rich gel phase domains. This observation is tentatively attributed to differences in the presentation of the GalCer epitope in the two phases, resulting in differences in availability of the ligand for antibody binding. The complementary information obtained by swiftly switching between SEEC and fluorescence (including TIR fluorescence) imaging modes was used to support the data interpretation. The simplicity and generic applicability of the concept is discussed in terms of microfluidic applications.
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Affiliation(s)
- Anders Gunnarsson
- Department of Applied Physics, Division of Biological Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
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195
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Wiącek AE. Influence of dipalmitoylphosphatidylcholine (or dioleoylphosphatidylcholine) and phospholipase A2 enzyme on the properties of emulsions. J Colloid Interface Sci 2012; 373:75-83. [DOI: 10.1016/j.jcis.2011.09.037] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Revised: 09/15/2011] [Accepted: 09/16/2011] [Indexed: 10/17/2022]
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196
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Nagaraj K, Arunachalam S. Studies on outer-sphere electron transfer reactions of surfactant–cobalt(III) complexes with iron(II) in liposome (dipalmitoylphosphotidylcholine) vesicles. TRANSIT METAL CHEM 2012. [DOI: 10.1007/s11243-012-9605-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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197
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González H C, Volkmann UG, Retamal MJ, Cisternas M, Sarabia MA, López KA. Thermal behavior of 1,2-dipalmitoyl-sn-3-phosphoglycerocholine bi- and multi-layers, deposited with physical vapor deposition under ellipsometric growth control. J Chem Phys 2012; 136:134709. [PMID: 22482582 DOI: 10.1063/1.3698486] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
1,2-dipalmitoyl-sn-3-phosphoglycerocholine membranes were deposited onto a silicon substrate (Si/SiO(2)) using physical vapor deposition with in situ ellipsometric thickness control. Along several heating cycles it was possible to identify well-defined boundaries for gel, ripple, liquid crystalline, and fluid-disordered phases. Particularly, the second order transition between gel and ripple phase was clearly identified in the range of ~28-34 °C using Raman spectroscopy. Atomic force microscopy and imaging ellipsometry (IE) were used to observe and characterize the ripple phase undulations of period λ = 20.8 nm and average height h = 19.95 nm along the temperature interval of ~34 to 40 °C. Clusters/agglomerations heights of more than twice the membrane thickness were observed with IE, induced by heating cycles.
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Affiliation(s)
- Carmen González H
- Facultad de Física, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860-Santiago, 7820436 Chile.
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198
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199
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Zimmermann R, Küttner D, Renner L, Kaufmann M, Werner C. Fluidity modulation of phospholipid bilayers by electrolyte ions: insights from fluorescence microscopy and microslit electrokinetic experiments. J Phys Chem A 2012; 116:6519-25. [PMID: 22304400 DOI: 10.1021/jp212364q] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Fluidity and charging of supported bilayer lipid membranes (sBLMs) prepared from 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) were studied by fluorescence recovery after photobleaching (FRAP) and microslit electrokinetic measurements at varying pH and ionic composition of the electrolyte. Measurements in neutral electrolytes (KCl, NaCl) revealed a strong correlation between the membrane fluidity and the membrane charging due to unsymmetrical water ion adsorption (OH(-) ≫ H(3)O(+)). The membrane fluidity significantly decreased below the isoelectric point of 3.9, suggesting a phase transition in the bilayer. The interactions of both chaotropic anions and strongly kosmotropic cations with the zwitterionic lipids were found to be related with nearly unhindered lipid mobility in the acidic pH range. While for the chaotropic anions the observed effect correlates with the increased negative net charge at low pH, no correlation was found between the changes in the membrane fluidity and charge in the presence of kosmotropic cations. We discuss the observed phenomena with respect to the interaction of the electrolyte ions with the lipid headgroup and the influence of this process on the headgroup orientation and hydration as well as on the lipid packaging.
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Affiliation(s)
- Ralf Zimmermann
- Leibniz Institute of Polymer Research Dresden, Max Bergmann Center of Biomaterials Dresden, Hohe Strasse 6, 01069 Dresden, Germany.
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200
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Direct measurement of the mechanical properties of lipid phases in supported bilayers. Biophys J 2012; 102:L01-3. [PMID: 22225813 DOI: 10.1016/j.bpj.2011.11.4001] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 11/08/2011] [Accepted: 11/21/2011] [Indexed: 11/23/2022] Open
Abstract
Biological membranes define not only the cell boundaries but any compartment within the cell. To some extent, the functionality of membranes is related to the elastic properties of the lipid bilayer and the mechanical and hydrophobic matching with functional membrane proteins. Supported lipid bilayers (SLBs) are valid biomimetic systems for the study of membrane biophysical properties. Here, we acquired high-resolution topographic and quantitative mechanics data of phase-separated SLBs using a recent atomic force microscopy (AFM) imaging mode based on force measurements. This technique allows us to quantitatively map at high resolution the mechanical differences of lipid phases at different loading forces. We have applied this approach to evaluate the contribution of the underlying hard support in the determination of the elastic properties of SLBs and to determine the adequate indentation range for obtaining reliable elastic moduli values. At ~200 pN, elastic forces dominated the force-indentation response and the sample deformation was <20% of the bilayer thickness, at which the contribution of the support was found to be negligible. The obtained Young's modulus (E) of 19.3 MPa and 28.1 MPa allowed us to estimate the area stretch modulus (k(A)) as 106 pN/nm and 199 pN/nm and the bending stiffness (k(c)) as 18 k(B)T and 57 k(B)T for the liquid and gel phases, respectively.
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