Advances in Symmetric and Asymmetric Lipid Membranes

A special issue of Membranes (ISSN 2077-0375). This special issue belongs to the section "Biological Membrane Composition and Structures".

Deadline for manuscript submissions: 31 May 2024 | Viewed by 12828

Special Issue Editor

Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14850, USA
Interests: biophysics; lipid bilayers; lipid–lipid interations; protein or peptide–lipid interactions; phase diagrams

Special Issue Information

Dear Colleagues,

Cellular membranes are complex in both composition and function. The lipid matrix of cellular membranes is composed of a variety of lipids with different chemical structures and physicochemical properties, which can yield coexistence of phases. The fundamental lipid–lipid and/or protein-lipid interactions in these membranes play important roles in cell function, transport of small molecules and ions, signaling, protein sorting, signal transduction, virus assembly, and cell death.

Interestingly, biological membranes are asymmetric lipid bilayers with a distinct lipid composition in the individual leaflets. Moreover, the loss of membrane asymmetry might be crucial to define health and diseases. Lately, a large effort has been employed in the development of new methods to create asymmetric lipid bilayers in vitro.

In addition to studies of biological membranes in real cells, model membranes prepared in vitro or in silico experiments offer a robust mimetic system to investigate the many properties of lipid membranes. These systems are excellent models to investigate events relevant to biological membranes, and for elucidating how proteins, anesthetics, drugs, or any exogenous molecules interact with the lipid bilayer.

We welcome contributions, original research articles, comprehensive reviews, and short communications focusing on aspects of model membranes and biological membranes. We welcome researchers working in the challenging areas of life and physical sciences to contribute to the advances of symmetric and asymmetric lipid membranes.

Dr. Thais A. Enoki
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Membranes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (9 papers)

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Research

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16 pages, 1914 KiB  
Article
Breakdown of Phospholipid Asymmetry Triggers ADAM17-Mediated Rescue Events in Cells Undergoing Apoptosis
by Maria Sperrhacke, Sinje Leitzke, Björn Ahrens and Karina Reiss
Membranes 2023, 13(8), 720; https://doi.org/10.3390/membranes13080720 - 05 Aug 2023
Viewed by 943
Abstract
ADAM17, a prominent member of the “Disintegrin and Metalloproteinase” (ADAM) family, controls vital cellular functions through the cleavage of transmembrane substrates, including epidermal growth factor receptor (EGFR) ligands such as transforming growth factor (TGF)-alpha and Epiregulin (EREG). Several ADAM17 substrates are relevant to [...] Read more.
ADAM17, a prominent member of the “Disintegrin and Metalloproteinase” (ADAM) family, controls vital cellular functions through the cleavage of transmembrane substrates, including epidermal growth factor receptor (EGFR) ligands such as transforming growth factor (TGF)-alpha and Epiregulin (EREG). Several ADAM17 substrates are relevant to oncogenesis and tumor growth. We have presented evidence that surface exposure of phosphatidylserine (PS) is pivotal for ADAM17 to exert sheddase activity. The scramblase Xkr8 is instrumental for calcium-independent exposure of PS in apoptotic cells. Xkr8 can be dually activated by caspase-3 and by kinases. In this investigation, we examined whether Xkr8 would modulate ADAM17 activity under apoptotic and non-apoptotic conditions. Overexpression of Xkr8 in HEK293T cells led to significantly increased caspase-dependent as well as PMA-induced release of EREG and TGF-alpha. Conversely, siRNA-mediated downregulation of Xkr8 in colorectal Caco-2 cancer cells led to decreased PS externalization upon induction of apoptosis, which was accompanied by reduced shedding of endogenously expressed EREG and reduced cell survival. We conclude that Xkr8 shares with conventional scramblases the propensity to upmodulate the ADAM-sheddase function. Liberation of growth factors could serve a rescue function in cells on the pathway to apoptotic death. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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17 pages, 6322 KiB  
Article
Critical Role of Molecular Packing in Lo Phase Membrane Solubilization
by Nicolas Puff
Membranes 2023, 13(7), 652; https://doi.org/10.3390/membranes13070652 - 07 Jul 2023
Viewed by 598
Abstract
Membrane solubilization induced by Triton X-100 (TX-100) was investigated. Different membrane compositions and phase states were studied along the detergent titration. Expected solubilization profiles were obtained but new information is provided. The fluorescence of nitrobenzoxadiazole (NBD)-labeled lipids indicates that the liquid-ordered (Lo)/liquid-disordered (Ld) [...] Read more.
Membrane solubilization induced by Triton X-100 (TX-100) was investigated. Different membrane compositions and phase states were studied along the detergent titration. Expected solubilization profiles were obtained but new information is provided. The fluorescence of nitrobenzoxadiazole (NBD)-labeled lipids indicates that the liquid-ordered (Lo)/liquid-disordered (Ld) phase coexistence is barely unaffected at sub-solubilizing detergent concentrations and highlights the vesicle-to-micelle transition. Moreover, the location of the NBD group in the bilayer emphasizes a detergent–membrane interaction in the case of the insoluble Lo phase membrane. It has also been shown that the molecular packing of the membrane loosens in the presence of TX-100, regardless of the solubilization profile. Motivated by studies on GPMVs, the solubilization of less ordered Lo phase membranes was considered in order to improve the effect of molecular packing on the extent of solubilization. Membranes composed of SM and Chol in an equimolar ratio doped with different amounts of PC were studied. The more ordered the Lo phase membrane is in the absence of detergent, the less likely it is to be solubilized. Furthermore, and in contrast to what is observed for membranes exhibiting an Lo/Ld phase coexistence, a very small decrease in the molecular packing of the Lo phase membrane radically modifies the extent of solubilization. These results have implications for the reliability of TX-100 insolubility as a method to detect ordered domains. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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14 pages, 2070 KiB  
Article
Influence of Membrane Asymmetry on OmpF Insertion, Orientation and Function
by Annemarie Donoghue, Mathias Winterhalter and Thomas Gutsmann
Membranes 2023, 13(5), 517; https://doi.org/10.3390/membranes13050517 - 16 May 2023
Cited by 1 | Viewed by 994
Abstract
The effect of asymmetric membranes containing lipopolysaccharides (LPS) on the outer membrane protein F (OmpF) reconstitution, channel orientation, and antibiotic permeation across the outer membrane was investigated. After forming an asymmetric planar lipid bilayer composed of LPS on one and phospholipids on the [...] Read more.
The effect of asymmetric membranes containing lipopolysaccharides (LPS) on the outer membrane protein F (OmpF) reconstitution, channel orientation, and antibiotic permeation across the outer membrane was investigated. After forming an asymmetric planar lipid bilayer composed of LPS on one and phospholipids on the other side, the membrane channel OmpF was added. The ion current recordings demonstrate that LPS has a strong influence on the OmpF membrane insertion, orientation, and gating. Enrofloxacin was used as an example of an antibiotic interacting with the asymmetric membrane and with OmpF. The enrofloxacin caused the blockage of the ion current through the OmpF, depending on the side of addition, the transmembrane voltage applied, and the composition of the buffer. Furthermore, the enrofloxacin changed the phase behavior of the LPS-containing membranes, demonstrating that its membrane activity influences the function of OmpF and potentially the membrane permeability. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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12 pages, 22174 KiB  
Article
Real Space and Time Imaging of Collective Headgroup Dipole Motions in Zwitterionic Lipid Bilayers
by Dima Bolmatov, C. Patrick Collier, Dmitry Zav’yalov, Takeshi Egami and John Katsaras
Membranes 2023, 13(4), 442; https://doi.org/10.3390/membranes13040442 - 18 Apr 2023
Cited by 4 | Viewed by 1706
Abstract
Lipid bilayers are supramolecular structures responsible for a range of processes, such as transmembrane transport of ions and solutes, and sorting and replication of genetic materials, to name just a few. Some of these processes are transient and currently, cannot be visualized in [...] Read more.
Lipid bilayers are supramolecular structures responsible for a range of processes, such as transmembrane transport of ions and solutes, and sorting and replication of genetic materials, to name just a few. Some of these processes are transient and currently, cannot be visualized in real space and time. Here, we developed an approach using 1D, 2D, and 3D Van Hove correlation functions to image collective headgroup dipole motions in zwitterionic phospholipid bilayers. We show that both 2D and 3D spatiotemporal images of headgroup dipoles are consistent with commonly understood dynamic features of fluids. However, analysis of the 1D Van Hove function reveals lateral transient and re-emergent collective dynamics of the headgroup dipoles—occurring at picosecond time scales—that transmit and dissipate heat at longer times, due to relaxation processes. At the same time, the headgroup dipoles also generate membrane surface undulations due a collective tilting of the headgroup dipoles. A continuous intensity band of headgroup dipole spatiotemporal correlations—at nanometer length and nanosecond time scales—indicates that dipoles undergo stretching and squeezing elastic deformations. Importantly, the above mentioned intrinsic headgroup dipole motions can be externally stimulated at GHz-frequency scale, enhancing their flexoelectric and piezoelectric capabilities (i.e., increased conversion efficiency of mechanical energy into electric energy). In conclusion, we discuss how lipid membranes can provide molecular-level insights about biological learning and memory, and as platforms for the development of the next generation of neuromorphic computers. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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17 pages, 2337 KiB  
Article
A Small-Angle Neutron Scattering, Calorimetry and Densitometry Study to Detect Phase Boundaries and Nanoscale Domain Structure in a Binary Lipid Mixture
by Natalie Krzyzanowski, Lionel Porcar and Ursula Perez-Salas
Membranes 2023, 13(3), 323; https://doi.org/10.3390/membranes13030323 - 10 Mar 2023
Cited by 1 | Viewed by 1026
Abstract
Techniques that can probe nanometer length scales, such as small-angle neutron scattering (SANS), have become increasingly popular to detect phase separation in membranes. But to extract the phase composition and domain structure from the SANS traces, complementary information is needed. Here, we present [...] Read more.
Techniques that can probe nanometer length scales, such as small-angle neutron scattering (SANS), have become increasingly popular to detect phase separation in membranes. But to extract the phase composition and domain structure from the SANS traces, complementary information is needed. Here, we present a SANS, calorimetry and densitometry study of a mixture of two saturated lipids that exhibits solidus–liquidus phase coexistence: 1,2-dipalmitoyl-d62-sn-glycero-3-phosphocholine (dDPPC, tail-deuterated DPPC) and 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC). With calorimetry, we investigated the phase diagram for this system and found that the boundary traces for both multilamellar vesicles (MLVs) as well as 50 nm unilamellar vesicles overlap. Because the solidus boundary was mostly inaccessible by calorimetry, we investigated it by both SANS and molecular volume measurements for a 1:1 dDPPC:DLPC lipid mixture. From the temperature behavior of the molecular volume for the 1:1 dDPPC:DLPC mixture, as well as the individual molecular volume of each lipid species, we inferred that the liquidus phase consists of only fluid-state lipids while the solidus phase consists of lipids that are in gel-like states. Using this solidus–liquidus phase model, the SANS data were analyzed with an unrestricted shape model analysis software: MONSA. The resulting fits show irregular domains with dendrite-like features as those previously observed on giant unilamellar vesicles (GUVs). The surface pair correlation function describes a characteristic domain size for the minority phase that decreases with temperature, a behavior found to be consistent with a concomitant decrease in membrane mismatch between the liquidus and solidus phases. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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Review

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12 pages, 931 KiB  
Review
Asymmetric Distribution of Plasmalogens and Their Roles—A Mini Review
by Masanori Honsho and Yukio Fujiki
Membranes 2023, 13(9), 764; https://doi.org/10.3390/membranes13090764 - 29 Aug 2023
Viewed by 1047
Abstract
Plasmalogens are a unique family of cellular glycerophospholipids that contain a vinyl-ether bond. The synthesis of plasmalogens is initiated in peroxisomes and completed in the endoplasmic reticulum. Plasmalogens are transported to the post-Golgi compartment, including endosomes and plasma membranes, in a manner dependent [...] Read more.
Plasmalogens are a unique family of cellular glycerophospholipids that contain a vinyl-ether bond. The synthesis of plasmalogens is initiated in peroxisomes and completed in the endoplasmic reticulum. Plasmalogens are transported to the post-Golgi compartment, including endosomes and plasma membranes, in a manner dependent on ATP, but not vesicular transport. Plasmalogens are preferentially localized in the inner leaflet of the plasma membrane in a manner dependent on P4-type ATPase ATP8B2, that associates with the CDC50 subunit. Plasmalogen biosynthesis is spatiotemporally regulated by a feedback mechanism that senses the amount of plasmalogens in the inner leaflet of the plasma membrane and controls the stability of fatty acyl-CoA reductase 1 (FAR1), the rate-limiting enzyme for plasmalogen biosynthesis. The physiological consequences of such asymmetric localization and homeostasis of plasmalogens are discussed in this review. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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14 pages, 1627 KiB  
Review
Building Asymmetric Lipid Bilayers for Molecular Dynamics Simulations: What Methods Exist and How to Choose One?
by Emily H. Chaisson, Frederick A. Heberle and Milka Doktorova
Membranes 2023, 13(7), 629; https://doi.org/10.3390/membranes13070629 - 29 Jun 2023
Cited by 3 | Viewed by 1939
Abstract
The compositional asymmetry of biological membranes has attracted significant attention over the last decade. Harboring more differences from symmetric membranes than previously appreciated, asymmetric bilayers have proven quite challenging to study with familiar concepts and techniques, leaving many unanswered questions about the reach [...] Read more.
The compositional asymmetry of biological membranes has attracted significant attention over the last decade. Harboring more differences from symmetric membranes than previously appreciated, asymmetric bilayers have proven quite challenging to study with familiar concepts and techniques, leaving many unanswered questions about the reach of the asymmetry effects. One particular area of active research is the computational investigation of composition- and number-asymmetric lipid bilayers with molecular dynamics (MD) simulations. Offering a high level of detail into the organization and properties of the simulated systems, MD has emerged as an indispensable tool in the study of membrane asymmetry. However, the realization that results depend heavily on the protocol used for constructing the asymmetric bilayer models has sparked an ongoing debate about how to choose the most appropriate approach. Here we discuss the underlying source of the discrepant results and review the existing methods for creating asymmetric bilayers for MD simulations. Considering the available data, we argue that each method is well suited for specific applications and hence there is no single best approach. Instead, the choice of a construction protocol—and consequently, its perceived accuracy—must be based primarily on the scientific question that the simulations are designed to address. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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21 pages, 2326 KiB  
Review
A Guide to Your Desired Lipid-Asymmetric Vesicles
by Mona Krompers and Heiko Heerklotz
Membranes 2023, 13(3), 267; https://doi.org/10.3390/membranes13030267 - 23 Feb 2023
Cited by 3 | Viewed by 2048
Abstract
Liposomes are prevalent model systems for studies on biological membranes. Recently, increasing attention has been paid to models also representing the lipid asymmetry of biological membranes. Here, we review in-vitro methods that have been established to prepare free-floating vesicles containing different compositions of [...] Read more.
Liposomes are prevalent model systems for studies on biological membranes. Recently, increasing attention has been paid to models also representing the lipid asymmetry of biological membranes. Here, we review in-vitro methods that have been established to prepare free-floating vesicles containing different compositions of the classic two-chain glycero- or sphingolipids in their outer and inner leaflet. In total, 72 reports are listed and assigned to four general strategies that are (A) enzymatic conversion of outer leaflet lipids, (B) re-sorting of lipids between leaflets, (C) assembly from different monolayers and (D) exchange of outer leaflet lipids. To guide the reader through this broad field of available techniques, we attempt to draw a road map that leads to the lipid-asymmetric vesicles that suit a given purpose. Of each method, we discuss advantages and limitations. In addition, various verification strategies of asymmetry as well as the role of cholesterol are briefly discussed. The ability to specifically induce lipid asymmetry in model membranes offers insights into the biological functions of asymmetry and may also benefit the technical applications of liposomes. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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Other

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13 pages, 682 KiB  
Perspective
Ordered Domain (Raft) Formation in Asymmetric Vesicles and Its Induction upon Loss of Lipid Asymmetry in Artificial and Natural Membranes
by Erwin London
Membranes 2022, 12(9), 870; https://doi.org/10.3390/membranes12090870 - 09 Sep 2022
Cited by 5 | Viewed by 1498
Abstract
Lipid asymmetry, the difference in the lipid composition in the inner and outer lipid monolayers (leaflets) of a membrane, is an important feature of eukaryotic plasma membranes. Investigation of the biophysical consequences of lipid asymmetry has been aided by advances in the ability [...] Read more.
Lipid asymmetry, the difference in the lipid composition in the inner and outer lipid monolayers (leaflets) of a membrane, is an important feature of eukaryotic plasma membranes. Investigation of the biophysical consequences of lipid asymmetry has been aided by advances in the ability to prepare artificial asymmetric membranes, especially by use of cyclodextrin-catalyzed lipid exchange. This review summarizes recent studies with artificial asymmetric membranes which have identified conditions in which asymmetry can induce or suppress the ability of membranes to form ordered domains (rafts). A consequence of the latter effect is that, under some conditions, a loss of asymmetry can induce ordered domain formation. An analogous study in plasma membrane vesicles has demonstrated that asymmetry can also suppress domain formation in natural membranes. Thus, it is possible that a loss of asymmetry can induce domain formation in vivo. Full article
(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)
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