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Pabst G, Keller S. Exploring membrane asymmetry and its effects on membrane proteins. Trends Biochem Sci 2024; 49:333-345. [PMID: 38355393 DOI: 10.1016/j.tibs.2024.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 01/08/2024] [Accepted: 01/19/2024] [Indexed: 02/16/2024]
Abstract
Plasma membranes utilize free energy to maintain highly asymmetric, non-equilibrium distributions of lipids and proteins between their two leaflets. In this review we discuss recent progress in quantitative research enabled by using compositionally controlled asymmetric model membranes. Both experimental and computational studies have shed light on the nuanced mechanisms that govern the structural and dynamic coupling between compositionally distinct bilayer leaflets. This coupling can increase the membrane bending rigidity and induce order - or lipid domains - across the membrane. Furthermore, emerging evidence indicates that integral membrane proteins not only respond to asymmetric lipid distributions but also exhibit intriguing asymmetric properties themselves. We propose strategies to advance experimental research, aiming for a deeper, quantitative understanding of membrane asymmetry, which carries profound implications for cellular physiology.
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Affiliation(s)
- Georg Pabst
- Biophysics, Institute of Molecular Bioscience (IMB), NAWI Graz, University of Graz, Graz 8010, Austria; BioTechMed-Graz, Graz, Austria; Field of Excellence BioHealth, University of Graz, Graz, Austria.
| | - Sandro Keller
- Biophysics, Institute of Molecular Bioscience (IMB), NAWI Graz, University of Graz, Graz 8010, Austria; BioTechMed-Graz, Graz, Austria; Field of Excellence BioHealth, University of Graz, Graz, Austria
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Krompers M, Heerklotz H. A Guide to Your Desired Lipid-Asymmetric Vesicles. MEMBRANES 2023; 13:267. [PMID: 36984654 PMCID: PMC10054703 DOI: 10.3390/membranes13030267] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 02/14/2023] [Accepted: 02/18/2023] [Indexed: 06/18/2023]
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 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.
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Affiliation(s)
- Mona Krompers
- Department of Pharmaceutical Technology and Biopharmacy, Institute for Pharmaceutical Sciences, University of Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Heiko Heerklotz
- Department of Pharmaceutical Technology and Biopharmacy, Institute for Pharmaceutical Sciences, University of Freiburg, 79104 Freiburg im Breisgau, Germany
- Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, ON M5S 3M2, Canada
- Signalling Research Centers BIOSS and CIBSS, University of Freiburg, 79085 Freiburg im Breisgau, Germany
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Heerklotz H, London E. Kiss and Run Asymmetric Vesicles to Investigate Coupling. Biophys J 2019; 117:1009-1011. [PMID: 31477242 DOI: 10.1016/j.bpj.2019.07.053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 07/29/2019] [Indexed: 10/26/2022] Open
Affiliation(s)
- Heiko Heerklotz
- Institute of Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany; Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada; Signalling Research Centers BIOSS and CIBSS, Freiburg, Germany.
| | - Erwin London
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York.
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Drechsler C, Markones M, Choi JY, Frieling N, Fiedler S, Voelker DR, Schubert R, Heerklotz H. Preparation of Asymmetric Liposomes Using a Phosphatidylserine Decarboxylase. Biophys J 2018; 115:1509-1517. [PMID: 30266319 DOI: 10.1016/j.bpj.2018.08.036] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 08/18/2018] [Accepted: 08/21/2018] [Indexed: 01/08/2023] Open
Abstract
Lipid asymmetries between the outer and inner leaflet of the lipid bilayer exist in nearly all biological membranes. Although living cells spend great effort to adjust and maintain these asymmetries, little is known about the biophysical phenomena within asymmetric membranes and their role in cellular function. One reason for this lack of insight into such a fundamental membrane property is the fact that the majority of model-membrane studies have been performed on symmetric membranes. Our aim is to overcome this problem by employing a targeted, enzymatic reaction to prepare asymmetric liposomes with phosphatidylserine (PS) primarily in the inner leaflet. To achieve this goal, we use a recombinant version of a water soluble PS decarboxylase from Plasmodium knowlesi, which selectively decarboxylates PS in the outer leaflet, converting it to phosphatidylethanolamine. The extent of decarboxylation is quantified using high-performance thin-layer chromatography, and the local concentration of anionic PS in the outer leaflet is monitored in terms of the ζ potential. Starting, for example, with 21 mol % 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine sodium salt, the assay leads to liposomes with 21 mol % in the inner and 6 mol % PS in the outer leaflet. This asymmetry persists virtually unchanged for at least 4 days at 20°C and at least 2 days at 40°C. The use of a highly specific enzyme carries the advantage that a minor component such as PS can be adjusted without affecting or being affected by the other lipid species present in the model membrane. The phenomena governing the residual outside PS content are addressed but warrant further study.
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Affiliation(s)
- Carina Drechsler
- Institute for Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, Freiburg, Germany
| | - Marie Markones
- Institute for Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, Freiburg, Germany
| | - Jae-Yeon Choi
- Department of Medicine, National Jewish Health, Denver, Colorado
| | - Niklas Frieling
- Institute for Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany
| | - Sebastian Fiedler
- Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Canada
| | - Dennis R Voelker
- Department of Medicine, National Jewish Health, Denver, Colorado
| | - Rolf Schubert
- Institute for Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, Freiburg, Germany
| | - Heiko Heerklotz
- Institute for Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, Freiburg, Germany; Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Canada.
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St. Clair JR, Wang Q, Li G, London E. Preparation and Physical Properties of Asymmetric Model Membrane Vesicles. SPRINGER SERIES IN BIOPHYSICS 2017. [DOI: 10.1007/978-981-10-6244-5_1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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Diedrich D, Moita AJR, Rüther A, Frieg B, Reiss GJ, Hoeppner A, Kurz T, Gohlke H, Lüdeke S, Kassack MU, Hansen FK. α-Aminoxy Oligopeptides: Synthesis, Secondary Structure, and Cytotoxicity of a New Class of Anticancer Foldamers. Chemistry 2016; 22:17600-17611. [PMID: 27573537 DOI: 10.1002/chem.201602521] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Indexed: 11/11/2022]
Abstract
α-Aminoxy peptides are peptidomimetic foldamers with high proteolytic and conformational stability. To gain an improved synthetic access to α-aminoxy oligopeptides we used a straightforward combination of solution- and solid-phase-supported methods and obtained oligomers that showed a remarkable anticancer activity against a panel of cancer cell lines. We solved the first X-ray crystal structure of an α-aminoxy peptide with multiple turns around the helical axis. The crystal structure revealed a right-handed 28 -helical conformation with precisely two residues per turn and a helical pitch of 5.8 Å. By 2D ROESY experiments, molecular dynamics simulations, and CD spectroscopy we were able to identify the 28 -helix as the predominant conformation in organic solvents. In aqueous solution, the α-aminoxy peptides exist in the 28 -helical conformation at acidic pH, but exhibit remarkable changes in the secondary structure with increasing pH. The most cytotoxic α-aminoxy peptides have an increased propensity to take up a 28 -helical conformation in the presence of a model membrane. This indicates a correlation between the 28 -helical conformation and the membranolytic activity observed in mode of action studies, thereby providing novel insights in the folding properties and the biological activity of α-aminoxy peptides.
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Affiliation(s)
- Daniela Diedrich
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Ana J Rodrigues Moita
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Anja Rüther
- Institut für Pharmazeutische Wissenschaften, Albert-Ludwigs-Universität Freiburg, 79104, Freiburg, Germany
| | - Benedikt Frieg
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Guido J Reiss
- Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Astrid Hoeppner
- X-Ray Facility and Crystal Farm, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Thomas Kurz
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Holger Gohlke
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Steffen Lüdeke
- Institut für Pharmazeutische Wissenschaften, Albert-Ludwigs-Universität Freiburg, 79104, Freiburg, Germany
| | - Matthias U Kassack
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Finn K Hansen
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
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Molnar D, Linders J, Mayer C, Schubert R. Insertion stability of poly(ethylene glycol)-cholesteryl-based lipid anchors in liposome membranes. Eur J Pharm Biopharm 2016; 103:51-61. [DOI: 10.1016/j.ejpb.2016.03.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Revised: 03/15/2016] [Accepted: 03/21/2016] [Indexed: 10/22/2022]
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Pereira de Souza T, Holzer M, Stano P, Steiniger F, May S, Schubert R, Fahr A, Luisi PL. New Insights into the Growth and Transformation of Vesicles: A Free-Flow Electrophoresis Study. J Phys Chem B 2015; 119:12212-23. [PMID: 26340300 DOI: 10.1021/acs.jpcb.5b05057] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The spontaneous formation of lipid vesicles, in particular fatty acid vesicles, is considered an important physical process at the roots of cellular life. It has been demonstrated previously that the addition of fatty acid micelles to preformed vesicles induces vesicle self-reproduction by a growth-division mechanism. Despite multiple experimental efforts, it remains unresolved how vesicles rearrange upon the addition of fresh membrane-forming compounds, and whether solutes that are initially encapsulated inside the mother vesicles are evenly redistributed among the daughter ones. Here we investigate the growth-division of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) vesicles, which, following the addition of oleate micelles, form mixed oleate/POPC vesicles. Our approach is based on free-flow electrophoresis (FFE) and cryogenic transmission electronmicroscopy (cryo-TEM). Two new features emerge from this study. FFE analysis unexpectedly reveals that the uptake of oleate micelles by POPC vesicles follows two different pathways depending on the micelles/vesicles ratio. At low oleate molar fractions (<0.35), plain incorporation of oleate into pre-existing POPC vesicles is our dominant observation. In contrast, oleate-rich and oleate-poor daughter vesicles are generated from parent POPC vesicles when the oleate molar fraction exceeds 0.35. Cryo-TEM reveals that when ferritin-filled vesicles grow and divide, some vesicles contain ferritin at increased concentrations, others are empty. Intriguingly, in some cases, ferritin appears to be highly concentrated inside the vesicles. These observations imply a specific redistribution (partitioning) of encapsulated solutes among nascent vesicles during the growth-division steps. We have interpreted our observations by assuming that freshly added oleate molecules are taken-up preferentially (cooperatively) by oleate-rich membrane regions that form spontaneously in POPC/oleate vesicles when a certain threshold (oleate molar fraction ca. 0.35) is surpassed. The proposed cooperative mechanism could be based on differential microscopic constants for oleate/oleic acid dynamics in oleate-rich and oleate-poor membrane regions, which eventually generate populations of oleate-rich and oleate-poor vesicles.
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Affiliation(s)
- Tereza Pereira de Souza
- Institut für Pharmazie, Friedrich Schiller Universität Jena ; Lessingstrasse 8, D-07743 Jena, Germany
| | - Martin Holzer
- Department of Pharmaceutical Technology and Biopharmacy, Albert Ludwigs University Freiburg , D-79104 Freiburg, Germany
| | - Pasquale Stano
- Science Department, Roma Tre University ; Viale G. Marconi 446, I-00146 Rome, Italy
| | - Frank Steiniger
- Elektronenmikroskopisches Zentrum, Friedrich Schiller Universität Jena ; Ziegelmühlenweg 1, D-07743 Jena, Germany
| | - Sylvio May
- Department of Physics, North Dakota State University , Fargo North Dakota 58108-6050, United States
| | - Rolf Schubert
- Department of Pharmaceutical Technology and Biopharmacy, Albert Ludwigs University Freiburg , D-79104 Freiburg, Germany
| | - Alfred Fahr
- Institut für Pharmazie, Friedrich Schiller Universität Jena ; Lessingstrasse 8, D-07743 Jena, Germany
| | - Pier Luigi Luisi
- Science Department, Roma Tre University ; Viale G. Marconi 446, I-00146 Rome, Italy
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Son M, London E. The dependence of lipid asymmetry upon phosphatidylcholine acyl chain structure. J Lipid Res 2012; 54:223-31. [PMID: 23093551 DOI: 10.1194/jlr.m032722] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Lipid asymmetry, the difference in inner and outer leaflet lipid composition, is an important feature of biomembranes. By utilizing our recently developed MβCD-catalyzed exchange method, the effect of lipid acyl chain structure upon the ability to form asymmetric membranes was investigated. Using this approach, SM was efficiently introduced into the outer leaflet of vesicles containing various phosphatidylcholines (PC), but whether the resulting vesicles were asymmetric (SM outside/PC inside) depended upon PC acyl chain structure. Vesicles exhibited asymmetry using PC with two monounsaturated chains of >14 carbons; PC with one saturated and one unsaturated chain; and PC with phytanoyl chains. Vesicles were most weakly asymmetric using PC with two 14 carbon monounsaturated chains or with two polyunsaturated chains. To define the origin of this behavior, transverse diffusion (flip-flop) of lipids in vesicles containing various PCs was compared. A correlation between asymmetry and transverse diffusion was observed, with slower transverse diffusion in vesicles containing PCs that supported lipid asymmetry. Thus, asymmetric vesicles can be prepared using a wide range of acyl chain structures, but fast transverse diffusion destroys lipid asymmetry. These properties may constrain acyl chain structure in asymmetric natural membranes to avoid short or overly polyunsaturated acyl chains.
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Affiliation(s)
- Mijin Son
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY, USA
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