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Goodwin ZA, Kornyshev AA. Cracking Ion Pairs in the Electrical Double Layer of Ionic Liquids. Electrochim Acta 2022. [DOI: 10.1016/j.electacta.2022.141163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Bagheri Y, Ali AA, You M. Current Methods for Detecting Cell Membrane Transient Interactions. Front Chem 2020; 8:603259. [PMID: 33365301 PMCID: PMC7750205 DOI: 10.3389/fchem.2020.603259] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2020] [Accepted: 10/16/2020] [Indexed: 12/28/2022] Open
Abstract
Short-lived cell membrane complexes play a key role in regulating cell signaling and communication. Many of these complexes are formed based on low-affinity and transient interactions among various lipids and proteins. New techniques have emerged to study these previously overlooked membrane transient interactions. Exciting functions of these transient interactions have been discovered in cellular events such as immune signaling, host-pathogen interactions, and diseases such as cancer. In this review, we have summarized current experimental methods that allow us to detect and analyze short-lived cell membrane protein-protein, lipid-protein, and lipid-lipid interactions. These methods can provide useful information about the strengths, kinetics, and/or spatial patterns of membrane transient interactions. However, each method also has its own limitations. We hope this review can be used as a guideline to help the audience to choose proper approaches for studying membrane transient interactions in different membrane trafficking and cell signaling events.
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Affiliation(s)
| | | | - Mingxu You
- Department of Chemistry, University of Massachusetts, Amherst, MA, United States
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Role of Transmembrane Proteins for Phase Separation and Domain Registration in Asymmetric Lipid Bilayers. Biomolecules 2019; 9:biom9080303. [PMID: 31349669 PMCID: PMC6723173 DOI: 10.3390/biom9080303] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 07/19/2019] [Accepted: 07/22/2019] [Indexed: 02/05/2023] Open
Abstract
It is well known that the formation and spatial correlation of lipid domains in the two apposed leaflets of a bilayer are influenced by weak lipid–lipid interactions across the bilayer’s midplane. Transmembrane proteins span through both leaflets and thus offer an alternative domain coupling mechanism. Using a mean-field approximation of a simple bilayer-type lattice model, with two two-dimensional lattices stacked one on top of the other, we explore the role of this “structural” inter-leaflet coupling for the ability of a lipid membrane to phase separate and form spatially correlated domains. We present calculated phase diagrams for various effective lipid–lipid and lipid–protein interaction strengths in membranes that contain a binary lipid mixture in each leaflet plus a small amount of added transmembrane proteins. The influence of the transmembrane nature of the proteins is assessed by a comparison with “peripheral” proteins, which result from the separation of one single integral protein into two independent units that are no longer structurally connected across the bilayer. We demonstrate that the ability of membrane-spanning proteins to facilitate domain formation requires sufficiently strong lipid–protein interactions. Weak lipid–protein interactions generally tend to inhibit phase separation in a similar manner for transmembrane as for peripheral proteins.
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Weiner MD, Feigenson GW. Molecular Dynamics Simulations Reveal Leaflet Coupling in Compositionally Asymmetric Phase-Separated Lipid Membranes. J Phys Chem B 2019; 123:3968-3975. [PMID: 31009218 DOI: 10.1021/acs.jpcb.9b03488] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The eukaryotic plasma membrane has an asymmetric distribution of its component lipids. Rafts that result from liquid-liquid phase separation are a feature of its exoplasmic leaflet, but how these exoplasmic leaflet domains are coupled to the cytoplasmic leaflet is not understood. These rafts can be studied in model membranes of three-component mixtures that produce coexisting liquid ordered (Lo) and liquid disordered (Ld) domains. We conducted all-atom molecular dynamics simulations of compositionally asymmetric lipid bilayers that reflect a more realistic model of the plasma membrane. One leaflet contained phase-separated domains with phosphatidylcholine and cholesterol, representing the exoplasmic leaflet, whereas the other contained phosphatidylethanolamine, phosphatidylserine, and cholesterol, which are the predominant components of the cytoplasmic leaflet. Inspired by findings of domain alignment across the two leaflets in compositionally symmetric model membranes, we examined the coupling between the two leaflets to see how the single-phase cytoplasmic leaflet would respond to phase separation in the other leaflet and if information could be communicated across the membrane. We found the region of the single-phase leaflet apposing the Lo domain to be slightly more ordered and thicker than the region apposing the Ld domain. The region across from the Lo domain is somewhat enriched in cholesterol and significantly depleted of polyunsaturated lipids.
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Almeida PF. How to Determine Lipid Interactions in Membranes from Experiment Through the Ising Model. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:21-40. [PMID: 30589556 DOI: 10.1021/acs.langmuir.8b03054] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The determination and the meaning of interactions in lipid bilayers are discussed and interpreted through the Ising model. Originally developed to understand phase transitions in ferromagnetic systems, the Ising model applies equally well to lipid bilayers. In the case of a membrane, the essence of the Ising model is that each lipid is represented by a site on a lattice and that the interaction of each site with its nearest neighbors is represented by an energy parameter ω. To calculate the thermodynamic properties of the system, such as the enthalpy, the Gibbs energy, and the heat capacity, the partition function is derived. The calculation of the configurational entropy factor in the partition function, however, requires approximations or the use of Monte Carlo (MC) simulations. Those approximations are described. Ultimately, MC simulations are used in combination with experiment to determine the interaction parameters ω in lipid bilayers. Several experimental approaches are described, which can be used to obtain interaction parameters. They include nearest-neighbor recognition, differential scanning calorimetry, and Förster resonance energy transfer. Those approaches are most powerful when used in combination of MC simulations of Ising models. Lipid membranes of different compositions are discussed, which have been studied with these approaches. They include mixtures of cholesterol, saturated (ordered) phospholipids, and unsaturated (disordered) phospholipids. The interactions between those lipid species are examined as a function of molecular properties such as the degree of unsaturation and the acyl chain length. The general rule that emerges is that interactions between different lipids are usually unfavorable. The exception is that cholesterol interacts favorably with saturated (ordered) phospholipids. However, the interaction of cholesterol with unsaturated phospholipids becomes extremely unfavorable as the degree of unsaturation increases.
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Affiliation(s)
- Paulo F Almeida
- Department of Chemistry and Biochemistry , University of North Carolina Wilmington , Wilmington , North Carolina 28403 , United States
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Wang C, Almeida PF, Regen SL. Net Interactions That Push Cholesterol Away from Unsaturated Phospholipids Are Driven by Enthalpy. Biochemistry 2018; 57:6637-6643. [DOI: 10.1021/acs.biochem.8b00983] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chang Wang
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Paulo F. Almeida
- Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, North Carolina 28403, United States
| | - Steven L. Regen
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
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Almeida PF, Carter FE, Kilgour KM, Raymonda MH, Tejada E. Heat Capacity of DPPC/Cholesterol Mixtures: Comparison of Single Bilayers with Multibilayers and Simulations. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:9798-9809. [PMID: 30088940 DOI: 10.1021/acs.langmuir.8b01774] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The excess heat capacity (Δ C p) of mixtures of dipalmitoylphosphatidylcholine (DPPC) and cholesterol (Chol) is examined in detail in large unilamellar vesicles (LUVs), both experimentally, using differential scanning calorimetry (DSC), and theoretically, using a three-state Ising model. The model postulates that DPPC can access three conformational states: gel, liquid-disordered (Ld), and liquid-ordered (Lo). The Lo state, however, is only available if coupled with interaction with an adjacent Chol. Δ C p was calculated using Monte Carlo simulations on a lattice and compared to experiment. The DSC results in LUVs are compared with literature data on multilamellar vesicles (MLVs). The enthalpy change of the complete phase transition from gel to Ld is identical in LUVs and MLVs, and the melting temperatures ( Tm) are similar. However, the DSC curves in LUVs are significantly broader, and the maxima of Δ C p are accordingly smaller. The parameters in the Ising model were chosen to match the DSC curves in LUVs and the nearest-neighbor recognition (NNR) data. The model reproduces the NNR data very well. It also reproduces the phase transition in DPPC, the freezing point depression induced by Chol, and the broad component of Δ C p in DPPC/Chol LUVs. However, there is a sharp component, between 5 and 15 mol % Chol, that the model does not reproduce. The broad component of Δ C p becomes dominant as Chol concentration increases, indicating that it involves melting of the Lo phase. Because the simulations reproduce this component, the conclusions regarding the nature of the phase transition at high Chol concentrations and the structure of the Lo phase are important: there is no true phase separation in DPPC/Chol LUVs. There are large domains of gel and Lo phase coexisting below Tm of DPPC, but above Tm the three states of DPPC are mixed with Chol, although clusters persist.
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Affiliation(s)
- Paulo F Almeida
- Department of Chemistry and Biochemistry , University of North Carolina Wilmington , Wilmington , North Carolina 28403 , United States
| | - Faith E Carter
- Department of Chemistry and Biochemistry , University of North Carolina Wilmington , Wilmington , North Carolina 28403 , United States
| | - Katie M Kilgour
- Department of Chemistry and Biochemistry , University of North Carolina Wilmington , Wilmington , North Carolina 28403 , United States
| | - Matthew H Raymonda
- Department of Chemistry and Biochemistry , University of North Carolina Wilmington , Wilmington , North Carolina 28403 , United States
| | - Emmanuel Tejada
- Department of Chemistry and Biochemistry , University of North Carolina Wilmington , Wilmington , North Carolina 28403 , United States
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Weiner MD, Feigenson GW. Presence and Role of Midplane Cholesterol in Lipid Bilayers Containing Registered or Antiregistered Phase Domains. J Phys Chem B 2018; 122:8193-8200. [DOI: 10.1021/acs.jpcb.8b03949] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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Fowler PW, Williamson JJ, Sansom MSP, Olmsted PD. Roles of Interleaflet Coupling and Hydrophobic Mismatch in Lipid Membrane Phase-Separation Kinetics. J Am Chem Soc 2016; 138:11633-42. [PMID: 27574865 PMCID: PMC5025830 DOI: 10.1021/jacs.6b04880] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
![]()
Characterizing
the nanoscale dynamic organization within lipid
bilayer
membranes is central
to our understanding of cell membranes at a molecular level. We investigate
phase separation and communication across leaflets in ternary lipid
bilayers, including saturated lipids with between 12 and 20 carbons
per tail. Coarse-grained molecular dynamics simulations reveal a novel
two-step kinetics due to hydrophobic mismatch, in which the initial
response of the apposed leaflets upon quenching is to increase local
asymmetry (antiregistration), followed by dominance of symmetry (registration)
as the bilayer equilibrates. Antiregistration can become thermodynamically
preferred if domain size is restricted below ∼20 nm, with implications
for the symmetry of rafts and nanoclusters in cell membranes, which
have similar reported sizes. We relate our findings to theory derived
from a semimicroscopic model in which the leaflets experience a “direct”
area-dependent coupling, and an “indirect” coupling
that arises from hydrophobic mismatch and is most important at domain
boundaries. Registered phases differ in composition from antiregistered
phases, consistent with a direct coupling between the leaflets. Increased
hydrophobic mismatch purifies the phases, suggesting that it contributes
to the molecule-level lipid immiscibility. Our results demonstrate
an interplay of competing interleaflet couplings that affect phase
compositions and kinetics, and lead to a length scale that
can influence lateral and transverse bilayer organization within cells.
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Affiliation(s)
- Philip W Fowler
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford, OX1 3QU, U.K
| | - John J Williamson
- Department of Physics, Institute for Soft Matter Synthesis and Metrology, Georgetown University , 37th and O Streets, N.W., Washington, D.C. 20057, United States
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford, OX1 3QU, U.K
| | - Peter D Olmsted
- Department of Physics, Institute for Soft Matter Synthesis and Metrology, Georgetown University , 37th and O Streets, N.W., Washington, D.C. 20057, United States
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Williamson JJ, Olmsted PD. Kinetics of symmetry and asymmetry in a phase-separating bilayer membrane. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:052721. [PMID: 26651737 DOI: 10.1103/physreve.92.052721] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Indexed: 06/05/2023]
Abstract
We simulate a phase-separating bilayer in which the leaflets experience a direct coupling favoring local compositional symmetry ("registered" bilayer phases), and an indirect coupling due to hydrophobic mismatch that favors strong local asymmetry ("antiregistered" bilayer phases). For wide ranges of overall leaflet compositions, multiple competing states are possible. For estimated physical parameters, a quenched bilayer may first evolve toward a metastable state more asymmetric than if the leaflets were uncorrelated; subsequently, it must nucleate to reach its equilibrium, more symmetric, state. These phase-transition kinetics exhibit characteristic signatures through which fundamental and opposing interleaflet interactions may be probed. We emphasize how bilayer phase diagrams with a separate axis for each leaflet can account for overall and local symmetry or asymmetry, and capture a range of observations in the experiment and simulation literature.
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Affiliation(s)
- J J Williamson
- Department of Physics, Institute for Soft Matter Synthesis and Metrology, Georgetown University, 37th and O Streets, N.W., Washington, D.C. 20057, USA
| | - P D Olmsted
- Department of Physics, Institute for Soft Matter Synthesis and Metrology, Georgetown University, 37th and O Streets, N.W., Washington, D.C. 20057, USA
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