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Reconstituted lipid vesicles

Julia P Steringer, Walter Nickel
As illustrated by a diverse set of examples in this special issue, multiple mechanisms of protein secretion have been identified in eukaryotes that do not involve the endoplasmic reticulum (ER) and the Golgi apparatus. Here we focus on the type I pathway with Fibroblast Growth Factor 2 (FGF2) being the most prominent example. Unconventional secretion of FGF2 from cells is mediated by direct protein translocation across the plasma membrane. A unique feature of this process is the ability of FGF2 to form its own membrane translocation intermediate through oligomerization and membrane insertion...
February 16, 2018: Seminars in Cell & Developmental Biology
Dimitri Fayolle, Michele Fiore, Pasquale Stano, Peter Strazewski
Giant lipid vesicles (GVs) are emerging models for investigating the properties and reactivity of cell-like microcompartments, providing useful information about plausible protocellular structures in primitive times, as well as for the modern synthetic biology goal of constructing the first artificial cell from its reconstituted and partly modified components. Here we explore a novel methodology of GV purification by microfiltration under reduced pressure, operated by a simple apparatus. The method has been characterized in terms of flow rate, amount of lipid loss, quality of recovered GVs, and size distribution...
2018: PloS One
Huan Bao, Debasis Das, Nicholas A Courtney, Yihao Jiang, Joseph S Briguglio, Xiaochu Lou, Daniel Roston, Qiang Cui, Baron Chanda, Edwin R Chapman
The fusion pore is the first crucial intermediate formed during exocytosis, yet little is known about the mechanisms that determine the size and kinetic properties of these transient structures. Here, we reduced the number of available SNAREs (proteins that mediate vesicle fusion) in neurons and observed changes in transmitter release that are suggestive of alterations in fusion pores. To investigate these changes, we employed reconstituted fusion assays using nanodiscs to trap pores in their initial open state...
February 8, 2018: Nature
Aymeric Chorlay, Abdou Rachid Thiam
Cells store excess energy in the form of neutral lipids that are synthesized and encapsulated within the endoplasmic reticulum intermonolayer space. The lipids next demix to form lipid droplets (LDs), which, surprisingly, bud off mostly toward the cytosol. This directional LD formation is critical to energy metabolism, but its mechanism remains poorly understood. Here, we reconstituted the LD formation topology by embedding artificial LDs into the intermonolayer space of bilayer vesicles. We provide experimental evidence that the droplet behavior in the membrane is recapitulated by the physics of three-phase wetting systems, dictated by the equilibrium of surface tensions...
February 6, 2018: Biophysical Journal
Rashmi Seneviratne, Sanobar Khan, Ellen Moscrop, Michael Rappolt, Stephen P Muench, Lars J C Jeuken, Paul A Beales
Hybrid vesicles composed of lipids and block copolymers hold promise for increasing liposome stability and providing a stable environment for membrane proteins. Recently we reported the successful functional reconstitution of the integral membrane protein cytochrome bo3 (ubiquinol oxidase) into hybrid vesicles composed of a blend of phospholipids and a block copolymer (PBd-PEO). We demonstrated that these novel membrane environments stabilise the enzymes' activity, prolonging their functional lifetime [Chem Commun...
January 31, 2018: Methods: a Companion to Methods in Enzymology
Nicholas A Ferraro, Michael Cascio
The glycine receptor (GlyR) belongs to a superfamily of pentameric ligand-gated ion channels (pLGICs) that mediate fast neurotransmission. GlyR typically modulates inhibitory transmission by antagonizing membrane depolarization through anion influx. Allosteric interactions between the receptor and its lipid surroundings affect receptor function, and cholesterol is essential for pLGIC activity. Cholesterol at compositions below ~33 mol percent has been shown to have negligible chemical activity, suggesting that specific interactions between membrane proteins and cholesterol become significant only at concentrations above this stoichiometric threshold...
January 22, 2018: Analytical Chemistry
Rahul Chadda, Lucy Cliff, Marley Brimberry, Janice L Robertson
The thermodynamic reasons why membrane proteins form stable complexes inside the hydrophobic lipid bilayer remain poorly understood. This is largely because of a lack of membrane-protein systems amenable for equilibrium studies and a limited number of methods for measuring these reactions. Recently, we reported the equilibrium dimerization of the CLC-ec1 Cl-/H+ transporter in lipid bilayers (Chadda et al. 2016. eLife, which provided a new type of model system for studying protein association in membranes...
January 10, 2018: Journal of General Physiology
Sunyia Hussain, Harris D Bernstein
Most proteins that reside in the bacterial outer membrane (OM) have a distinctive "β-barrel" architecture, but the assembly of these proteins is poorly understood. The spontaneous assembly of OM proteins (OMPs) into pure lipid vesicles has been studied extensively, but often requires non-physiological conditions and time scales and is strongly influenced by properties of the lipid bilayer including surface charge, thickness, and fluidity. Furthermore, the membrane insertion of OMPs in vivo is catalyzed by a heterooligomer called the β-barrel assembly machinery (Bam) complex...
January 8, 2018: Journal of Biological Chemistry
Giulia Morra, Asghar M Razavi, Kalpana Pandey, Harel Weinstein, Anant K Menon, George Khelashvili
Several class-A G protein-coupled receptor (GPCR) proteins act as constitutive phospholipid scramblases catalyzing the transbilayer translocation of >10,000 phospholipids per second when reconstituted into synthetic vesicles. To address the molecular mechanism by which these proteins facilitate rapid lipid scrambling, we carried out large-scale ensemble atomistic molecular dynamics simulations of the opsin GPCR. We report that, in the process of scrambling, lipid head groups traverse a dynamically revealed hydrophilic pathway in the region between transmembrane helices 6 and 7 of the protein while their hydrophobic tails remain in the bilayer environment...
December 18, 2017: Structure
Coline Prévost, Feng-Ching Tsai, Patricia Bassereau, Mijo Simunovic
The reshaping of the cell membrane is an integral part of many cellular phenomena, such as endocytosis, trafficking, the formation of filopodia, etc. Many different proteins associate with curved membranes because of their ability to sense or induce membrane curvature. Typically, these processes involve a multitude of proteins making them too complex to study quantitatively in the cell. We describe a protocol to reconstitute a curved membrane in vitro, mimicking a curved cellular structure, such as the endocytic neck...
December 7, 2017: Journal of Visualized Experiments: JoVE
Pasquale Stano, Emiliano Altamura, Fabio Mavelli
Important progresses have been achieved in the past years in the field of bottom-up synthetic biology, especially aiming at constructing cell-like systems based on lipid vesicles (liposomes) entrapping both biomolecules or synthetic compounds. These "synthetic cells" mimic the behaviour of biological cells but are constituted by a minimal number of components. One key aspect related to this research is the energetic needs of synthetic cells. Up to now, high-energy compounds have been given in order to drive biochemical reactions inside the vesicle lumen...
2017: Communicative & Integrative Biology
Anders Lundgren, Björn Johansson Fast, Stephan Block, Björn Agnarsson, Erik Reimhult, Anders Gunnarsson, Fredrik Höök
The function of integral membrane proteins is critically dependent on their naturally surrounding lipid membrane. Detergent-solubilized and purified membrane proteins are therefore often reconstituted into cell-membrane mimics and analyzed for their function with single-molecule microscopy. Expansion of this approach toward a broad range of pharmaceutically interesting drug targets and biomarkers however remains hampered by the fact that these proteins have low expression levels, and that detergent solubilization and reconstitution often cause protein conformational changes and loss of membrane-specific cofactors, which may impair protein function...
January 10, 2018: Nano Letters
Kalpana Pandey, Birgit Ploier, Michael A Goren, Joshua Levitz, George Khelashvili, Anant K Menon
The G protein-coupled receptor opsin is a phospholipid scramblase that facilitates rapid transbilayer phospholipid exchange in liposomes. The mechanism by which opsin scrambles lipids is unknown. It has been proposed that lipid translocation may occur at protein-protein interfaces of opsin dimers. To test this possibility, we rationally engineered QUAD opsin by tryptophan substitution of four lipid-facing residues in transmembrane helix 4 (TM4) that is known to be important for dimerization. Atomistic molecular dynamics simulations of wild type and QUAD opsins combined with continuum modeling revealed that the tryptophan substitutions lower the energetically unfavorable residual hydrophobic mismatch between TM4 and the membrane, reducing the drive of QUAD opsin to dimerize...
December 1, 2017: Scientific Reports
Andrew Jo, Hiofan Hoi, Hang Zhou, Manisha Gupta, Carlo D Montemagno
Planar lipid bilayer device, alternatively known as BLM, is a powerful tool to study functional properties of conducting membrane proteins such as ion channels and porins. In this work, we used BLM to study the prokaryotic voltage-gated sodium channel (Nav) NaChBac in a well-defined membrane environment. Navs are an essential component for the generation and propagation of electric signals in excitable cells. The successes in the biochemical, biophysical and crystallographic studies on prokaryotic Navs in recent years has greatly promoted the understanding of the molecular mechanism that underlies these proteins and their eukaryotic counterparts...
2017: PloS One
Massimo Bottini, Saida Mebarek, Karen L Anderson, Agnieszka Strzelecka-Kiliszek, Lukasz Bozycki, Ana Maria Sper Simão, Maytê Bolean, Pietro Ciancaglini, Joanna Bandorowicz Pikula, Slawomir Pikula, David Magne, Niels Volkmann, Dorit Hanein, José Luis Millán, Rene Buchet
BACKGROUND: Matrix vesicles (MVs) are released from hypertrophic chondrocytes and from mature osteoblasts, the cells responsible for endochondral and membranous ossification. Under pathological conditions, they can also be released from cells of non-skeletal tissues such as vascular smooth muscle cells. MVs are extracellular vesicles of approximately 100-300nm diameter harboring the biochemical machinery needed to induce mineralization. SCOPE OF THE REVIEW: The review comprehensively delineates our current knowledge of MV biology and highlights open questions aiming to stimulate further research...
March 2018: Biochimica et Biophysica Acta
Yihui Xu, Jan Kuhlmann, Martha Brennich, Karlo Komorowski, Reinhard Jahn, Claudia Steinem, Tim Salditt
SNAREs are known as an important family of proteins mediating vesicle fusion. For various biophysical studies, they have been reconstituted into supported single bilayers via proteoliposome adsorption and rupture. In this study we extended this method to the reconstitution of SNAREs into supported multilamellar lipid membranes, i.e. oriented multibilayer stacks, as an ideal model system for X-ray structure analysis (X-ray reflectivity and diffraction). The reconstitution was implemented through a pathway of proteomicelle, proteoliposome and multibilayer...
February 2018: Biochimica et Biophysica Acta
Víctor G Almendro-Vedia, Paolo Natale, Michael Mell, Stephanie Bonneau, Francisco Monroy, Frederic Joubert, Iván López-Montero
ATP synthase is a rotating membrane protein that synthesizes ATP through proton-pumping activity across the membrane. To unveil the mechanical impact of this molecular active pump on the bending properties of its lipid environment, we have functionally reconstituted the ATP synthase in giant unilamellar vesicles and tracked the membrane fluctuations by means of flickering spectroscopy. We find that ATP synthase rotates at a frequency of about 20 Hz, promoting large nonequilibrium deformations at discrete hot spots in lipid vesicles and thus inducing an overall membrane softening...
October 24, 2017: Proceedings of the National Academy of Sciences of the United States of America
Zhenyong Wu, Sathish Thiyagarajan, Ben O'Shaughnessy, Erdem Karatekin
Calcium-triggered exocytotic release of neurotransmitters and hormones from neurons and neuroendocrine cells underlies neuronal communication, motor activity and endocrine functions. The core of the neuronal exocytotic machinery is composed of soluble N-ethyl maleimide sensitive factor attachment protein receptors (SNAREs). Formation of complexes between vesicle-attached v- and plasma-membrane anchored t-SNAREs in a highly regulated fashion brings the membranes into close apposition. Small, soluble proteins called Complexins (Cpx) and calcium-sensing Synaptotagmins cooperate to block fusion at low resting calcium concentrations, but trigger release upon calcium increase...
2017: Frontiers in Molecular Neuroscience
Kimberly Matulef, Francis I Valiyaveetil
Patch-clamp electrophysiology is the standard technique used for the high-resolution functional measurements on ion channels. While studies using patch clamp are commonly carried out following ion channel expression in a heterologous system such as Xenopus oocytes or tissue culture cells, these studies can also be carried out using ion channels reconstituted into lipid vesicles. In this chapter, we describe the methodology for reconstituting ion channels into liposomes and the procedure for the generation of unilamellar blisters from these liposomes that are suitable for patch clamp...
2018: Methods in Molecular Biology
Han-Yuan Liu, Wei-Liang Chen, Christopher K Ober, Susan Daniel
Reconstituted supported lipid bilayers (SLB) are widely used as in vitro cell-surface models because they are compatible with a variety of surface-based analytical techniques. However, one of the challenges of using SLBs as a model of the cell surface is the limited complexity in membrane composition, including the incorporation of transmembrane proteins and lipid diversity that may impact the activity of those proteins. Additionally, it is challenging to preserve the transmembrane protein native orientation, function, and mobility in SLBs...
October 24, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
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