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Socrier L, Steinem C. Pore-spanning membranes as a tool to investigate lateral lipid membrane heterogeneity. Methods Enzymol 2024; 700:455-483. [PMID: 38971610 DOI: 10.1016/bs.mie.2024.02.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/08/2024]
Abstract
Over the years, it has become more and more obvious that lipid membranes show a very complex behavior. This behavior arises in part from the large number of different kinds of lipids and proteins and how they dynamically interact with each other. In vitro studies using artificial membrane systems have shed light on the heterogeneity based on lipid-lipid interactions in multicomponent bilayer mixtures. Inspired by the raft hypothesis, the coexistence of liquid-disordered (ld) and liquid-ordered (lo) phases has drawn much attention. It was shown that ternary lipid mixtures containing low- and high-melting temperature lipids and cholesterol can phase separate into a lo phase enriched in the high-melting lipids and cholesterol and a ld phase enriched in the low-melting lipids. Depending on the model membrane system under investigation, different domain sizes, shapes, and mobilities have been found. Here, we describe how to generate phase-separated lo/ld phases in model membrane systems termed pore-spanning membranes (PSMs). These PSMs are prepared on porous silicon substrates with pore sizes in the micrometer regime. A proper functionalization of the top surface of the substrates is required to achieve the spreading of giant unilamellar vesicles (GUVs) to obtain PSMs. Starting with lo/ld phase-separated GUVs lead to membrane heterogeneities in the PSMs. Depending on the functionalization strategy of the top surface of the silicon substrate, different membrane heterogeneities are observed in the PSMs employing fluorescence microscopy. A quantitative analysis of the heterogeneity as well as the dynamics of the lipid domains is described.
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Affiliation(s)
- Larissa Socrier
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany
| | - Claudia Steinem
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany; Institute of Organic and Biomolecular Chemistry, Georg-August Universität, Göttingen, Germany.
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Kalyana Sundaram RV, Bera M, Coleman J, Weerakkody JS, Krishnakumar SS, Ramakrishnan S. Native Planar Asymmetric Suspended Membrane for Single-Molecule Investigations: Plasma Membrane on a Chip. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2205567. [PMID: 36328714 DOI: 10.1002/smll.202205567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Indexed: 06/16/2023]
Abstract
Cellular plasma membranes, in their role as gatekeepers to the external environment, host numerous protein assemblies and lipid domains that manage the movement of molecules into and out of cells, regulate electric potential, and direct cell signaling. The ability to investigate these roles on the bilayer at a single-molecule level in a controlled, in vitro environment while preserving lipid and protein architectures will provide deeper insights into how the plasma membrane works. A tunable silicon microarray platform that supports stable, planar, and asymmetric suspended lipid membranes (SLIM) using synthetic and native plasma membrane vesicles for single-molecule fluorescence investigations is developed. Essentially, a "plasma membrane-on-a-chip" system that preserves lipid asymmetry and protein orientation is created. By harnessing the combined potential of this platform with total internal reflection fluorescence (TIRF) microscopy, the authors are able to visualize protein complexes with single-molecule precision. This technology has widespread applications in biological processes that happen at the cellular membranes and will further the knowledge of lipid and protein assemblies.
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Affiliation(s)
- Ramalingam Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Jonathan S Weerakkody
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Shyam S Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Neurology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT, 06520, USA
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Sannigrahi A, Rai VH, Chalil MV, Chakraborty D, Meher SK, Roy R. A Versatile Suspended Lipid Membrane System for Probing Membrane Remodeling and Disruption. MEMBRANES 2022; 12:1190. [PMID: 36557095 PMCID: PMC9784602 DOI: 10.3390/membranes12121190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Revised: 10/12/2022] [Accepted: 10/18/2022] [Indexed: 06/17/2023]
Abstract
Artificial membrane systems can serve as models to investigate molecular mechanisms of different cellular processes, including transport, pore formation, and viral fusion. However, the current, such as SUVs, GUVs, and the supported lipid bilayers suffer from issues, namely high curvature, heterogeneity, and surface artefacts, respectively. Freestanding membranes provide a facile solution to these issues, but current systems developed by various groups use silicon or aluminum oxide wafers for fabrication that involves access to a dedicated nanolithography facility and high cost while conferring poor membrane stability. Here, we report the development, characterization and applications of an easy-to-fabricate suspended lipid bilayer (SULB) membrane platform leveraging commercial track-etched porous filters (PCTE) with defined microwell size. Our SULB system offers a platform to study the lipid composition-dependent structural and functional properties of membranes with exceptional stability. With dye entrapped in PCTE microwells by SULB, we show that sphingomyelin significantly augments the activity of pore-forming toxin, Cytolysin A (ClyA) and the pore formation induces lipid exchange between the bilayer leaflets. Further, we demonstrate high efficiency and rapid kinetics of membrane fusion by dengue virus in our SULB platform. Our suspended bilayer membrane mimetic offers a novel platform to investigate a large class of biomembrane interactions and processes.
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Dietz J, Oelkers M, Hubrich R, Pérez-Lara A, Jahn R, Steinem C, Janshoff A. Forces, Kinetics, and Fusion Efficiency Altered by the Full-Length Synaptotagmin-1 -PI(4,5)P 2 Interaction in Constrained Geometries. NANO LETTERS 2022; 22:1449-1455. [PMID: 34855407 DOI: 10.1021/acs.nanolett.1c02491] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
A mechanism for full-length synaptotagmin-1 (syt-1) to interact with anionic bilayers and to promote fusion in the presence of SNAREs is proposed. Colloidal probe force spectroscopy in conjunction with tethered particle motion monitoring showed that in the absence of Ca2+ the binding of syt-1 to membranes depends on the presence and content of PI(4,5)P2. Addition of Ca2+ switches the interaction forces from weak to strong, eventually exceeding the cohesion of the C2A domain of syt-1 leading to partial unfolding of the protein. Fusion of single unilamellar vesicles equipped with syt-1 and synaptobrevin 2 with planar pore-spanning target membranes containing PS and PI(4,5)P2 shows an almost complete suppression of stalled intermediate fusion states and an accelerated fusion kinetics in the presence of Ca2+, which is further enhanced upon addition of ATP.
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Affiliation(s)
- Joern Dietz
- Institute for Physical Chemistry, Georg-August Universität, Tammannstr. 6, 37077 Göttingen, Germany
| | - Marieelen Oelkers
- Institute for Physical Chemistry, Georg-August Universität, Tammannstr. 6, 37077 Göttingen, Germany
| | - Raphael Hubrich
- Institute for Organic and Biomolecular Chemistry, Georg-August Universität, Tammannstr. 2, 37077 Göttingen, Germany
| | - Angel Pérez-Lara
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Faβberg 11, 37077 Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Faβberg 11, 37077 Göttingen, Germany
| | - Claudia Steinem
- Institute for Organic and Biomolecular Chemistry, Georg-August Universität, Tammannstr. 2, 37077 Göttingen, Germany
| | - Andreas Janshoff
- Institute for Physical Chemistry, Georg-August Universität, Tammannstr. 6, 37077 Göttingen, Germany
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Mühlenbrock P, Sari M, Steinem C. In vitro single vesicle fusion assays based on pore-spanning membranes: merits and drawbacks. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2021; 50:239-252. [PMID: 33320298 PMCID: PMC8071798 DOI: 10.1007/s00249-020-01479-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 11/06/2020] [Accepted: 11/09/2020] [Indexed: 12/22/2022]
Abstract
Neuronal fusion mediated by soluble N-ethylmaleimide-sensitive-factor attachment protein receptors (SNAREs) is a fundamental cellular process by which two initially distinct membranes merge resulting in one interconnected structure to release neurotransmitters into the presynaptic cleft. To get access to the different stages of the fusion process, several in vitro assays have been developed. In this review, we provide a short overview of the current in vitro single vesicle fusion assays. Among those assays, we developed a single vesicle assay based on pore-spanning membranes (PSMs) on micrometre-sized pores in silicon, which might overcome some of the drawbacks associated with the other membrane architectures used for investigating fusion processes. Prepared by spreading of giant unilamellar vesicles with reconstituted t-SNAREs, PSMs provide an alternative tool to supported lipid bilayers to measure single vesicle fusion events by means of fluorescence microscopy. Here, we discuss the diffusive behaviour of the reconstituted membrane components as well as that of the fusing synthetic vesicles with reconstituted synaptobrevin 2 (v-SNARE). We compare our results with those obtained if the synthetic vesicles are replaced by natural chromaffin granules under otherwise identical conditions. The fusion efficiency as well as the different fusion states observable in this assay by means of both lipid mixing and content release are illuminated.
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Affiliation(s)
- Peter Mühlenbrock
- Georg-August-Universität Göttingen, Institute of Organic and Biomolecular Chemistry, Tammannstr. 2, 37077, Göttingen, Germany
| | - Merve Sari
- Georg-August-Universität Göttingen, Institute of Organic and Biomolecular Chemistry, Tammannstr. 2, 37077, Göttingen, Germany
| | - Claudia Steinem
- Georg-August-Universität Göttingen, Institute of Organic and Biomolecular Chemistry, Tammannstr. 2, 37077, Göttingen, Germany.
- Max-Planck-Institute for Dynamics and Self Organization, Am Faßberg 17, 37077, Göttingen, Germany.
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Fusion Pore Formation Observed during SNARE-Mediated Vesicle Fusion with Pore-Spanning Membranes. Biophys J 2020; 119:151-161. [PMID: 32533941 DOI: 10.1016/j.bpj.2020.05.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Revised: 05/22/2020] [Accepted: 05/26/2020] [Indexed: 12/27/2022] Open
Abstract
Planar pore-spanning membranes (PSMs) have been shown to be a versatile tool to resolve elementary steps of the neuronal fusion process. However, in previous studies, we monitored only lipid mixing between fusing large unilamellar vesicles and PSMs and did not gather information about the formation of fusion pores. To address this important step of the fusion process, we entrapped sulforhodamine B at self-quenching concentrations into large unilamellar vesicles containing the v-SNARE synaptobrevin 2, which were docked and fused with lipid-labeled PSMs containing the t-SNARE acceptor complex ΔN49 prepared on gold-coated porous silicon substrates. By dual-color spinning disk fluorescence microscopy with a time resolution of ∼20 ms, we could unambiguously distinguish between bursting vesicles, which was only rarely observed (<0.01%), and fusion pore formation. From the time-resolved dual-color fluorescence time traces, we were able to identify different fusion pathways, including remaining three-dimensional postfusion structures with released content and transient openings and closings of the fusion pores. Our results on fusion pore formation and lipid diffusion from the PSM into the fusing vesicle let us conclude that the content release, i.e., fusion pore formation after the merger of the two lipid membranes occurs almost simultaneously.
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Fusion assays for model membranes: a critical review. ADVANCES IN BIOMEMBRANES AND LIPID SELF-ASSEMBLY 2019. [DOI: 10.1016/bs.abl.2019.09.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
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