1
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Li D, Rocha-Roa C, Schilling MA, Reinisch KM, Vanni S. Lipid scrambling is a general feature of protein insertases. Proc Natl Acad Sci U S A 2024; 121:e2319476121. [PMID: 38621120 PMCID: PMC11047089 DOI: 10.1073/pnas.2319476121] [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: 11/07/2023] [Accepted: 03/13/2024] [Indexed: 04/17/2024] Open
Abstract
Glycerophospholipids are synthesized primarily in the cytosolic leaflet of the endoplasmic reticulum (ER) membrane and must be equilibrated between bilayer leaflets to allow the ER and membranes derived from it to grow. Lipid equilibration is facilitated by integral membrane proteins called "scramblases." These proteins feature a hydrophilic groove allowing the polar heads of lipids to traverse the hydrophobic membrane interior, similar to a credit card moving through a reader. Nevertheless, despite their fundamental role in membrane expansion and dynamics, the identity of most scramblases has remained elusive. Here, combining biochemical reconstitution and molecular dynamics simulations, we show that lipid scrambling is a general feature of protein insertases, integral membrane proteins which insert polypeptide chains into membranes of the ER and organelles disconnected from vesicle trafficking. Our data indicate that lipid scrambling occurs in the same hydrophilic channel through which protein insertion takes place and that scrambling is abolished in the presence of nascent polypeptide chains. We propose that protein insertases could have a so-far-overlooked role in membrane dynamics as scramblases.
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Affiliation(s)
- Dazhi Li
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Cristian Rocha-Roa
- Department of Biology, University of Fribourg, FribourgCH-1700, Switzerland
| | - Matthew A. Schilling
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Karin M. Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Stefano Vanni
- Department of Biology, University of Fribourg, FribourgCH-1700, Switzerland
- Swiss National Center for Competence in Research Bio-Inspired Materials, University of Fribourg, FribourgCH-1700, Switzerland
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2
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Bartoš L, Menon AK, Vácha R. Insertases scramble lipids: Molecular simulations of MTCH2. Structure 2024; 32:505-510.e4. [PMID: 38377988 PMCID: PMC11001264 DOI: 10.1016/j.str.2024.01.012] [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] [Received: 08/21/2023] [Revised: 11/30/2023] [Accepted: 01/24/2024] [Indexed: 02/22/2024]
Abstract
Scramblases play a pivotal role in facilitating bidirectional lipid transport across cell membranes, thereby influencing lipid metabolism, membrane homeostasis, and cellular signaling. MTCH2, a mitochondrial outer membrane protein insertase, has a membrane-spanning hydrophilic groove resembling those that form the lipid transit pathway in known scramblases. Employing both coarse-grained and atomistic molecular dynamics simulations, we show that MTCH2 significantly reduces the free energy barrier for lipid movement along the groove and therefore can indeed function as a scramblase. Notably, the scrambling rate of MTCH2 in silico is similar to that of voltage-dependent anion channel (VDAC), a recently discovered scramblase of the outer mitochondrial membrane, suggesting a potential complementary physiological role for these mitochondrial proteins. Finally, our findings suggest that other insertases which possess a hydrophilic path across the membrane like MTCH2, can also function as scramblases.
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Affiliation(s)
- Ladislav Bartoš
- CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic; National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Robert Vácha
- CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic; National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic; Department of Condensed Matter Physics, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic.
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3
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Dziura D, Dziura M, Marquardt D. Studying lipid flip-flop in asymmetric liposomes using 1H NMR and TR-SANS. Methods Enzymol 2024; 700:295-328. [PMID: 38971604 DOI: 10.1016/bs.mie.2024.02.012] [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
The specific spatial and temporal distribution of lipids in membranes play a crucial role in determining the biochemical and biophysical properties of the system. In nature, the asymmetric distribution of lipids is a dynamic process with ATP-dependent lipid transporters maintaining asymmetry, and passive transbilayer diffusion, that is, flip-flop, counteracting it. In this chapter, two probe-free techniques, 1H NMR and time-resolved small angle neutron scattering, are described in detail as methods of investigating lipid flip-flop rates in synthetic liposomes that have been generated with an asymmetric bilayer composition.
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Affiliation(s)
- Dominik Dziura
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Maksymilian Dziura
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Drew Marquardt
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada; Department of Physics, University of Windsor, Windsor, ON, Canada.
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4
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Jahn H, Bartoš L, Dearden GI, Dittman JS, Holthuis JCM, Vácha R, Menon AK. Phospholipids are imported into mitochondria by VDAC, a dimeric beta barrel scramblase. Nat Commun 2023; 14:8115. [PMID: 38065946 PMCID: PMC10709637 DOI: 10.1038/s41467-023-43570-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 11/13/2023] [Indexed: 12/17/2023] Open
Abstract
Mitochondria are double-membrane-bounded organelles that depend critically on phospholipids supplied by the endoplasmic reticulum. These lipids must cross the outer membrane to support mitochondrial function, but how they do this is unclear. We identify the Voltage Dependent Anion Channel (VDAC), an abundant outer membrane protein, as a scramblase-type lipid transporter that catalyzes lipid entry. On reconstitution into membrane vesicles, dimers of human VDAC1 and VDAC2 catalyze rapid transbilayer translocation of phospholipids by a mechanism that is unrelated to their channel activity. Coarse-grained molecular dynamics simulations of VDAC1 reveal that lipid scrambling occurs at a specific dimer interface where polar residues induce large water defects and bilayer thinning. The rate of phospholipid import into yeast mitochondria is an order of magnitude lower in the absence of VDAC homologs, indicating that VDACs provide the main pathway for lipid entry. Thus, VDAC isoforms, members of a superfamily of beta barrel proteins, moonlight as a class of phospholipid scramblases - distinct from alpha-helical scramblase proteins - that act to import lipids into mitochondria.
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Affiliation(s)
- Helene Jahn
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Ladislav Bartoš
- CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
| | - Grace I Dearden
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Jeremy S Dittman
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Joost C M Holthuis
- Department of Molecular Cell Biology, University of Osnabrück, Osnabrück, 49076, Germany
| | - Robert Vácha
- CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic.
- National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic.
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA.
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5
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Li D, Rocha-Roa C, Schilling MA, Reinisch KM, Vanni S. Lipid scrambling is a general feature of protein insertases. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.01.555937. [PMID: 37693532 PMCID: PMC10491306 DOI: 10.1101/2023.09.01.555937] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/12/2023]
Abstract
Glycerophospholipids are synthesized primarily in the cytosolic leaflet of the endoplasmic reticulum (ER) membrane and must be equilibrated between bilayer leaflets to allow the ER and membranes derived from it to grow. Lipid equilibration is facilitated by integral membrane proteins called "scramblases". These proteins feature a hydrophilic groove allowing the polar heads of lipids to traverse the hydrophobic membrane interior, similar to a credit-card moving through a reader. Nevertheless, despite their fundamental role in membrane expansion and dynamics, the identity of most scramblases has remained elusive. Here, combining biochemical reconstitution and molecular dynamics simulations, we show that lipid scrambling is a general feature of protein insertases, integral membrane proteins which insert polypeptide chains into membranes of the ER and organelles disconnected from vesicle trafficking. Our data indicate that lipid scrambling occurs in the same hydrophilic channel through which protein insertion takes place, and that scrambling is abolished in the presence of nascent polypeptide chains. We propose that protein insertases could have a so-far overlooked role in membrane dynamics as scramblases.
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Affiliation(s)
- Dazhi Li
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | | | - Matthew A Schilling
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Karin M Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Stefano Vanni
- Department of Biology, University of Fribourg, Switzerland
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6
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Bogdanov M. Renovating a double fence with or without notifying the next door and across the street neighbors: why the biogenic cytoplasmic membrane of Gram-negative bacteria display asymmetry? Emerg Top Life Sci 2023; 7:137-150. [PMID: 36960750 PMCID: PMC10725183 DOI: 10.1042/etls20230042] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2023] [Revised: 03/03/2023] [Accepted: 03/13/2023] [Indexed: 03/25/2023]
Abstract
The complex two-membrane organization of the envelope of Gram-negative bacteria imposes an unique biosynthetic and topological constraints that can affect translocation of lipids and proteins synthesized on the cytoplasm facing leaflet of the cytoplasmic (inner) membrane (IM), across the IM and between the IM and outer membrane (OM). Balanced growth of two membranes and continuous loss of phospholipids in the periplasmic leaflet of the IM as metabolic precursors for envelope components and for translocation to the OM requires a constant supply of phospholipids in the IM cytosolic leaflet. At present we have no explanation as to why the biogenic E. coli IM displays asymmetry. Lipid asymmetry is largely related to highly entropically disfavored, unequal headgroup and acyl group asymmetries which are usually actively maintained by active mechanisms. However, these mechanisms are largely unknown for bacteria. Alternatively, lipid asymmetry in biogenic IM could be metabolically controlled in order to maintain uniform bilayer growth and asymmetric transmembrane arrangement by balancing temporally the net rates of synthesis and flip-flop, inter IM and OM bidirectional flows and bilayer chemical and physical properties as spontaneous response. Does such flippase-less or 'lipid only", 'passive' mechanism of generation and maintenance of lipid asymmetry exists in the IM? The driving force for IM asymmetry can arise from the packing requirements imposed upon the bilayer system during cell division through disproportional distribution of two negatively curved phospholipids, phosphatidylethanolamine and cardiolipin, with consistent reciprocal tendency to increase and decrease lipid order in each membrane leaflet respectively.
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Affiliation(s)
- Mikhail Bogdanov
- Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, TX 77030, U.S.A
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7
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Brunner JD, Schenck S. Preparation of Proteoliposomes with Purified TMEM16 Protein for Accurate Measures of Lipid Scramblase Activity. Methods Mol Biol 2019; 1949:181-199. [PMID: 30790257 DOI: 10.1007/978-1-4939-9136-5_14] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The distribution of different lipid species between the two leaflets is tightly regulated and underlies the concerted action of distinct catalytic entities. While flippases and floppases establish membrane asymmetry, scramblases randomize the lipid distribution and play pivotal roles during blood clotting, apoptosis, and in processes such as N-linked glycosylation of proteins. The recent discovery of TMEM16 family members acting as scramblases has led to an increasing demand for developing protocols tailored for TMEM16 proteins to enable functional investigations of their scrambling activity. Here we describe a protocol for the expression, purification, and functional reconstitution of TMEM16 proteins into preformed liposomes and measurement of their scrambling activity using fluorescence-labeled lipid derivatives. The reconstitution involves extrusion of liposomes through a membrane, destabilization of liposomes using Triton X-100, and stepwise detergent removal by adsorption on styryl-beads. The scrambling assay is based on the selective bleaching of nitrobenzoxadiazol fluorescent lipids on the outer leaflet of liposomes by the membrane-impermeant reducing agent sodium dithionite. The assay allows conclusions on the substrate specificity and on the kinetics of the transported lipids as shown with the example of a Ca2+-activated TMEM16 scramblase from the fungus Nectria haematococca (nhTMEM16).
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Affiliation(s)
- Janine Denise Brunner
- Laboratory of Biomolecular Research, Division of Biology and Chemistry, Paul Scherrer Institut, Villigen, Switzerland.
| | - Stephan Schenck
- Laboratory of Biomolecular Research, Division of Biology and Chemistry, Paul Scherrer Institut, Villigen, Switzerland
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8
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Zheng L, Lin Y, Lu S, Zhang J, Bogdanov M. Biogenesis, transport and remodeling of lysophospholipids in Gram-negative bacteria. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:1404-1413. [PMID: 27956138 PMCID: PMC6162059 DOI: 10.1016/j.bbalip.2016.11.015] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 11/28/2016] [Accepted: 11/30/2016] [Indexed: 11/18/2022]
Abstract
Lysophospholipids (LPLs) are metabolic intermediates in bacterial phospholipid turnover. Distinct from their diacyl counterparts, these inverted cone-shaped molecules share physical characteristics of detergents, enabling modification of local membrane properties such as curvature. The functions of LPLs as cellular growth factors or potent lipid mediators have been extensively demonstrated in eukaryotic cells but are still undefined in bacteria. In the envelope of Gram-negative bacteria, LPLs are derived from multiple endogenous and exogenous sources. Although several flippases that move non-glycerophospholipids across the bacterial inner membrane were characterized, lysophospholipid transporter LplT appears to be the first example of a bacterial protein capable of facilitating rapid retrograde translocation of lyso forms of glycerophospholipids across the cytoplasmic membrane in Gram-negative bacteria. LplT transports lyso forms of the three bacterial membrane phospholipids with comparable efficiency, but excludes other lysolipid species. Once a LPL is flipped by LplT to the cytoplasmic side of the inner membrane, its diacyl form is effectively regenerated by the action of a peripheral enzyme, acyl-ACP synthetase/LPL acyltransferase (Aas). LplT-Aas also mediates a novel cardiolipin remodeling by converting its two lyso derivatives, diacyl or deacylated cardiolipin, to a triacyl form. This coupled remodeling system provides a unique bacterial membrane phospholipid repair mechanism. Strict selectivity of LplT for lyso lipids allows this system to fulfill efficient lipid repair in an environment containing mostly diacyl phospholipids. A rocker-switch model engaged by a pair of symmetric ion-locks may facilitate alternating substrate access to drive LPL flipping into bacterial cells. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.
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Affiliation(s)
- Lei Zheng
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston McGovern Medical School, 6431 Fannin Street, Houston, TX 77030, USA.
| | - Yibin Lin
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston McGovern Medical School, 6431 Fannin Street, Houston, TX 77030, USA
| | - Shuo Lu
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston McGovern Medical School, 6431 Fannin Street, Houston, TX 77030, USA
| | - Jiazhe Zhang
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston McGovern Medical School, 6431 Fannin Street, Houston, TX 77030, USA
| | - Mikhail Bogdanov
- Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston McGovern Medical School, 6431 Fannin Street, Houston, TX 77030, USA
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9
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Cotton RJ, Ploier B, Goren MA, Menon AK, Graumann J. flippant-An R package for the automated analysis of fluorescence-based scramblase assays. BMC Bioinformatics 2017; 18:146. [PMID: 28253836 PMCID: PMC5335725 DOI: 10.1186/s12859-017-1542-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Accepted: 02/08/2017] [Indexed: 11/30/2022] Open
Abstract
Background The lipid scrambling activity of protein extracts and purified scramblases is typically measured using a fluorescence-based assay. While the assay has yielded insight into the scramblase activity in crude membrane preparations, functional validation of candidate scramblases, stoichiometry of scramblase complexes as well as ATP-dependence of flippases, data analysis in its context has remained a task involving many manual steps. Results With the extension package “flippant” to R, a free software environment for statistical computing and graphics, we introduce an integrated solution for the analysis and publication-grade graphical presentation of dithionite scramblase assays and demonstrate its utility in revisiting an originally manual analysis from the publication record, closely reproducing the reported results. Conclusions “flippant” allows for quick, reproducible data analysis of scramblase activity assays and provides a platform for review, dissemination and extension of the strategies it employs. Electronic supplementary material The online version of this article (doi:10.1186/s12859-017-1542-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Richard J Cotton
- Research Division, Weill Cornell Medicine-Qatar, P.O.Box 24144, Doha, State of Qatar
| | - Birgit Ploier
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Michael A Goren
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Johannes Graumann
- Research Division, Weill Cornell Medicine-Qatar, P.O.Box 24144, Doha, State of Qatar. .,Current Address: Scientific Service Group Biomolecular Mass Spectrometry, Max Planck Institute for Heart and Lung Research, W.G. Kerckhoff Institute, Ludwigstr. 43, D-61231, Bad Nauheim, Germany.
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10
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Bevers EM, Williamson PL. Getting to the Outer Leaflet: Physiology of Phosphatidylserine Exposure at the Plasma Membrane. Physiol Rev 2016; 96:605-45. [PMID: 26936867 DOI: 10.1152/physrev.00020.2015] [Citation(s) in RCA: 294] [Impact Index Per Article: 36.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Phosphatidylserine (PS) is a major component of membrane bilayers whose change in distribution between inner and outer leaflets is an important physiological signal. Normally, members of the type IV P-type ATPases spend metabolic energy to create an asymmetric distribution of phospholipids between the two leaflets, with PS confined to the cytoplasmic membrane leaflet. On occasion, membrane enzymes, known as scramblases, are activated to facilitate transbilayer migration of lipids, including PS. Recently, two proteins required for such randomization have been identified: TMEM16F, a scramblase regulated by elevated intracellular Ca(2+), and XKR8, a caspase-sensitive protein required for PS exposure in apoptotic cells. Once exposed at the cell surface, PS regulates biochemical reactions involved in blood coagulation, and bone mineralization, and also regulates a variety of cell-cell interactions. Exposed on the surface of apoptotic cells, PS controls their recognition and engulfment by other cells. This process is exploited by parasites to invade their host, and in specialized form is used to maintain photoreceptors in the eye and modify synaptic connections in the brain. This review discusses what is known about the mechanism of PS exposure at the surface of the plasma membrane of cells, how actors in the extracellular milieu sense surface exposed PS, and how this recognition is translated to downstream consequences of PS exposure.
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Affiliation(s)
- Edouard M Bevers
- Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands; and Department of Biology, Amherst College, Amherst, Massachusetts
| | - Patrick L Williamson
- Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands; and Department of Biology, Amherst College, Amherst, Massachusetts
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11
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Williamson P. Phospholipid Scramblases. Lipid Insights 2016; 8:41-4. [PMID: 26843813 PMCID: PMC4737519 DOI: 10.4137/lpi.s31785] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 11/29/2015] [Accepted: 12/03/2015] [Indexed: 12/22/2022] Open
Abstract
The distribution of phospholipid types between the two leaflets of a membrane bilayer is a controlled feature of membrane structure. One of the two membrane catalytic activities governing this distribution randomizes the composition of the two leaflets-the phospholipid scramblases. Two proteins (Xkr8 and TMEM16F) required for the activation of these activities have been identified. One of these proteins (TMEM16F) is quite clearly a scramblase itself and provides insight into the mechanism by which transbilayer phospholipid movement is facilitated.
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12
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Substrate trajectory through phospholipid-transporting P4-ATPases. Biochem Soc Trans 2015; 42:1367-71. [PMID: 25233416 DOI: 10.1042/bst20140137] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A difference in the lipid composition between the two leaflets of the same membrane is a relatively simple instance of lipid compositional heterogeneity. The large activation energy barrier for transbilayer movement for some (but not all) membrane lipids creates a regime governed by active transport processes. An early step in eukaryote evolution was the development of a capacity for generating transbilayer compositional heterogeneity far from equilibrium by directly tapping energy from the ATP pool. The mechanism of the P-type ATPases that create lipid asymmetry is well understood in terms of ATP hydrolysis, but the trajectory taken by the phospholipid substrate through the enzyme is a matter of current active research. There are currently three different models for this trajectory, all with support by mutation/activity measurements and analogies with known atomic structures.
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13
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Surma MA, Szczepaniak A, Króliczewski J. Comparative studies on detergent-assisted apocytochrome b6 reconstitution into liposomal bilayers monitored by Zetasizer instruments. PLoS One 2014; 9:e111341. [PMID: 25423011 PMCID: PMC4244035 DOI: 10.1371/journal.pone.0111341] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Accepted: 10/01/2014] [Indexed: 11/19/2022] Open
Abstract
The present paper is a systematic, comparative study on the reconstitution of an apocytochrome b6 purified from a heterologous system using a detergent-free method and reconstitution into liposomes performed using three different detergents: SDS, Triton X-100 and DM, and two methods of detergent removal by dialysis and using Bio-Beads. The product size, its distribution and zeta potential, and other parameters were monitored throughout the process. We found that zeta potential of proteoliposomes is correlated with reconstitution efficiency and, as such, can serve as a quick and convenient quality control for reconstitution experiments. We also advocate using detergent-free protein purification methods as they allow for an unfettered choice of detergent for reconstitution, which is the most crucial factor influencing the final product parameters.
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Affiliation(s)
- Michał A. Surma
- Faculty of Biotechnology, University of Wroclaw, Wroclaw, Poland
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14
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Rajasekharan A, Francis VG, Gummadi SN. Biochemical evidence for energy-independent flippase activity in bovine epididymal sperm membranes: an insight into membrane biogenesis. Reproduction 2013; 146:209-20. [PMID: 23801779 DOI: 10.1530/rep-13-0121] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
During the maturation process spermatozoa undergo a series of changes in their lateral and horizontal lipid profiles. However, lipid metabolism in spermatozoa is not clearly understood for two reasons: i) the mature spermatozoa are devoid of endoplasmic reticulum, which is the major site of phospholipid (PL) synthesis in somatic cells, and ii) studies have been superficial due to the difficulty in culturing spermatozoa. We hypothesize that spermatozoa contain biogenic membrane flippases since immense changes in lipids occur during spermatogenic differentiation. To test this, we isolated spermatozoa from bovine epididymides and reconstituted the detergent extract of sperm membranes into proteoliposomes. In vitro assays showed that proteoliposomes reconstituted with sperm membrane proteins exhibit ATP-independent flip-flop movement of phosphatidylcholine (PC), phosphatidylserine, and phosphatidylglycerol. Half-life time of PC flipping was found to be ∼3.2±1 min for whole sperm membrane, which otherwise would have taken ∼11-12 h in the absence of protein. Further biochemical studies confirm the flip-flop movement to be protein-mediated, based on its sensitivity to protease and protein-modifying reagents. To further determine the cellular localization of flippases, we isolated mitochondria of spermatozoa and checked for ATP-independent flippase activity. Interestingly, mitochondrial membranes showed flip-flop movement but were specific for PC with half-life time of ∼5±2 min. Our results also suggest that spermatozoa have different populations of flippases and that their localization within the cellular compartments depends on the type of PL synthesis.
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Affiliation(s)
- Archita Rajasekharan
- Applied Industrial Microbiology Laboratory, Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600 036, India
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15
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Patra CR, Rupasinghe CN, Dutta SK, Bhattacharya S, Wang E, Spaller MR, Mukhopadhyay D. Chemically modified peptides targeting the PDZ domain of GIPC as a therapeutic approach for cancer. ACS Chem Biol 2012; 7:770-9. [PMID: 22292614 DOI: 10.1021/cb200536r] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
GIPC (GAIP-interacting protein, C terminus) represents a new target class for the discovery of chemotherapeutics. While many of the current generation of anticancer agents function by directly binding to intracellular kinases or cell surface receptors, the disruption of cytosolic protein-protein interactions mediated by non-enzymatic domains is an underdeveloped avenue for inhibiting cancer growth. One such example is the PDZ domain of GIPC. Previously we developed a molecular probe, the cell-permeable octapeptide CR1023 (N-myristoyl-PSQSSSEA), which diminished proliferation of pancreatic cancer cells. We have expanded upon that discovery using a chemical modification approach and here report a series of cell-permeable, side chain-modified lipopeptides that target the GIPC PDZ domain in vitro and in vivo. These peptides exhibit significant activity against pancreatic and breast cancers, both in cellular and animal models. CR1166 (N-myristoyl-PSQSK(εN-4-bromobenzoyl)SK(εN-4-bromobenzoyl)A), bearing two halogenated aromatic units on alternate side chains, was found to be the most active compound, with pronounced down-regulation of EGFR/1GF-1R expression. We hypothesize that these organic acid-modified residues extend the productive reach of the peptide beyond the canonical binding pocket, which defines the limit of accessibility for the native proteinogenic sequences that the PDZ domain has evolved to recognize. Cell permeability is achieved with N-terminal lipidation using myristate, rather than a larger CPP (cell-penetrating peptide) sequence. This, in conjunction with optimization of targeting through side chain modification, has yielded an approach that will allow the discovery and development of next-generation cellular probes for GIPC PDZ as well as for other PDZ domains.
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Affiliation(s)
- Chitta Ranjan Patra
- Department of Chemical Biology, Indian Institute of Chemical Technology, Uppal Road,
Tarnaka, Hyderabad-500607, AP, India
| | - Chamila N. Rupasinghe
- Department of Pharmacology
and
Toxicology, Dartmouth Medical School and Norris Cotton Cancer Center, Lebanon, New Hampshire, United States
| | | | | | | | - Mark R. Spaller
- Department of Pharmacology
and
Toxicology, Dartmouth Medical School and Norris Cotton Cancer Center, Lebanon, New Hampshire, United States
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16
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Rajasekharan A, Gummadi SN. Flip-flop of phospholipids in proteoliposomes reconstituted from detergent extract of chloroplast membranes: kinetics and phospholipid specificity. PLoS One 2011; 6:e28401. [PMID: 22174798 PMCID: PMC3236197 DOI: 10.1371/journal.pone.0028401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2011] [Accepted: 11/07/2011] [Indexed: 01/12/2023] Open
Abstract
Eukaryotic cells are compartmentalized into distinct sub-cellular organelles by lipid bilayers, which are known to be involved in numerous cellular processes. The wide repertoire of lipids, synthesized in the biogenic membranes like the endoplasmic reticulum and bacterial cytoplasmic membranes are initially localized in the cytosolic leaflet and some of these lipids have to be translocated to the exoplasmic leaflet for membrane biogenesis and uniform growth. It is known that phospholipid (PL) translocation in biogenic membranes is mediated by specific membrane proteins which occur in a rapid, bi-directional fashion without metabolic energy requirement and with no specificity to PL head group. A recent study reported the existence of biogenic membrane flippases in plants and that the mechanism of plant membrane biogenesis was similar to that found in animals. In this study, we demonstrate for the first time ATP independent and ATP dependent flippase activity in chloroplast membranes of plants. For this, we generated proteoliposomes from Triton X-100 extract of intact chloroplast, envelope membrane and thylakoid isolated from spinach leaves and assayed for flippase activity using fluorescent labeled phospholipids. Half-life time of flipping was found to be 6±1 min. We also show that: (a) intact chloroplast and envelope membrane reconstituted proteoliposomes can flip fluorescent labeled analogs of phosphatidylcholine in ATP independent manner, (b) envelope membrane and thylakoid reconstituted proteoliposomes can flip phosphatidylglycerol in ATP dependent manner, (c) Biogenic membrane ATP independent PC flipping activity is protein mediated and (d) the kinetics of PC translocation gets affected differently upon treatment with protease and protein modifying reagents.
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Affiliation(s)
- Archita Rajasekharan
- Department of Biotechnology, Indian Institute of Technology Madras, Chennai, India
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17
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Abstract
Cells have thousands of different lipids. In the plasma membrane, and in membranes of the late secretory and endocytotic pathways, these lipids are not evenly distributed over the two leaflets of the lipid bilayer. The basis for this transmembrane lipid asymmetry lies in the fact that glycerolipids are primarily synthesized on the cytosolic and sphingolipids on the noncytosolic surface of cellular membranes, that cholesterol has a higher affinity for sphingolipids than for glycerolipids. In addition, P4-ATPases, "flippases," actively translocate the aminophospholipids phosphatidylserine and phosphatidylethanolamine to the cytosolic surface. ABC transporters translocate lipids in the opposite direction but they generally act as exporters rather than "floppases." The steady state asymmetry of the lipids can be disrupted within seconds by the activation of phospholipases and scramblases. The asymmetric lipid distribution has multiple implications for physiological events at the membrane surface. Moreover, the active translocation also contributes to the generation of curvature in the budding of transport vesicles.
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Affiliation(s)
- Gerrit van Meer
- Bijvoet Center and Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands.
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18
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Is lipid flippase activity of SNARE transmembrane domains required for membrane fusion? FEBS Lett 2011; 585:1021-4. [PMID: 21362418 DOI: 10.1016/j.febslet.2011.02.033] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Revised: 02/23/2011] [Accepted: 02/23/2011] [Indexed: 11/22/2022]
Abstract
It has been suggested that lipids translocate between the outer and inner leaflets of fusing membranes, or flip-flop, to facilitate changes in bilayer leaflet areas at various stages of fusion. Here, we investigated the lipid flip activity of synthetic peptides that mimic SNARE transmembrane domains (TMDs). These peptides indeed induce flip of marker lipids. However, mutations that reduce flip activity do not diminish fusogenicity and cholesterol blocks flip much more efficiently than fusion. Therefore, our data do not support a role for flip in membrane fusion. On the other hand, the ability of SNARE TMDs to catalyze flip is consistent with a role of SNAREs in biogenic lipid flip.
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19
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Menon I, Huber T, Sanyal S, Banerjee S, Barré P, Canis S, Warren JD, Hwa J, Sakmar TP, Menon AK. Opsin is a phospholipid flippase. Curr Biol 2011; 21:149-53. [PMID: 21236677 DOI: 10.1016/j.cub.2010.12.031] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 11/17/2010] [Accepted: 12/14/2010] [Indexed: 11/19/2022]
Abstract
Polar lipids must flip-flop rapidly across biological membranes to sustain cellular life [1, 2], but flipping is energetically costly [3] and its intrinsic rate is low. To overcome this problem, cells have membrane proteins that function as lipid transporters (flippases) to accelerate flipping to a physiologically relevant rate. Flippases that operate at the plasma membrane of eukaryotes, coupling ATP hydrolysis to unidirectional lipid flipping, have been defined at a molecular level [2]. On the other hand, ATP-independent bidirectional flippases that translocate lipids in biogenic compartments, e.g., the endoplasmic reticulum, and specialized membranes, e.g., photoreceptor discs [4, 5], have not been identified even though their activity has been recognized for more than 30 years [1]. Here, we demonstrate that opsin is the ATP-independent phospholipid flippase of photoreceptor discs. We show that reconstitution of opsin into large unilamellar vesicles promotes rapid (τ<10 s) flipping of phospholipid probes across the vesicle membrane. This is the first molecular identification of an ATP-independent phospholipid flippase in any system. It reveals an unexpected activity for opsin and, in conjunction with recently available structural information on this G protein-coupled receptor [6, 7], significantly advances our understanding of the mechanism of ATP-independent lipid flip-flop.
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Affiliation(s)
- Indu Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
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20
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Abstract
The MsbA protein is an essential ABC (ATP-binding-cassette) superfamily member in Gram-negative bacteria. This 65 kDa membrane protein is thought to function as a homodimeric ATP-dependent lipid translocase or flippase that transports lipid A from the inner to the outer leaflet of the cytoplasmic membrane. We have previously shown that purified MsbA from Escherichia coli displays high ATPase activity, and binds to lipids and lipid-like molecules, including lipid A, with affinity in the low micromolar range. Bacterial membrane vesicles isolated from E. coli overexpressing His6-tagged MsbA displayed ATP-dependent translocation of several fluorescently NBD (7-nitrobenz-2-oxa-1,3-diazole)-labelled phospholipid species. Purified MsbA was reconstituted into proteoliposomes of E. coli lipid and its ability to translocate NBD-labelled lipid derivatives was characterized. In this system, the protein displayed maximal lipid flippase activity of 7.7 nmol of lipid translocated per mg of protein over a 20 min period for an acyl chain-labelled PE (phosphatidylethanolamine) derivative. The protein showed the highest rates of flippase activity when reconstituted into an E. coli lipid mixture. Substantial flippase activity was also observed for a variety of other NBD-labelled phospholipids and glycolipids, including molecules labelled on either the headgroup or the acyl chain. Lipid flippase activity required ATP hydrolysis, and was dependent on the concentration of ATP and NBD–lipid. Translocation of NBD–PE was inhibited by the presence of the putative physiological substrate lipid A. The present paper represents the first report of a direct measurement of the lipid flippase activity of purified MsbA in a reconstituted system.
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21
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Chemistry and Function of Phospholipids. FOOD SCIENCE AND TECHNOLOGY 2010. [DOI: 10.1201/9781420046649.ch2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/31/2023]
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22
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Abstract
The biosynthesis of glycoconjugates such as N-glycoproteins and GPI-anchored proteins in eukaryotes and cell wall peptidoglycan and lipopolysaccharide in bacteria requires lipid intermediates to be flipped rapidly across the endoplasmic reticulum or bacterial cytoplasmic membrane (so-called biogenic membranes). Rapid flipping is also required to normalize the number of glycerophospholipids in the two leaflets of the bilayer as the membrane expands in a growing cell. Although lipids diffuse rapidly in the plane of the membrane, the intrinsic rate at which they flip across membranes is very low. Biogenic membranes possess dedicated lipid transporters or flippases to increase flipping to a physiologically sufficient rate. The flippases are "ATP-independent" and facilitate "downhill" transport. Most predicted biogenic membrane flippases have not been identified at the molecular level, and the few flippases that have been identified by genetic approaches have not been biochemically validated. Here we summarize recent progress on this fundamental topic and speculate on the mechanism(s) by which biogenic membrane flippases facilitate transbilayer lipid movement.
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Affiliation(s)
- Sumana Sanyal
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065
| | - Anant K. Menon
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065
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23
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Nakano M, Fukuda M, Kudo T, Matsuzaki N, Azuma T, Sekine K, Endo H, Handa T. Flip-Flop of Phospholipids in Vesicles: Kinetic Analysis with Time-Resolved Small-Angle Neutron Scattering. J Phys Chem B 2009; 113:6745-8. [DOI: 10.1021/jp900913w] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Minoru Nakano
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Masakazu Fukuda
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Takayuki Kudo
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Naoya Matsuzaki
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Takuto Azuma
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Kazuhisa Sekine
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Hitoshi Endo
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Tetsurou Handa
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, and Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
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24
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Sahu SK, Gummadi SN. Flippase Activity in Proteoliposomes Reconstituted with Spinacea oleracea Endoplasmic Reticulum Membrane Proteins: Evidence of Biogenic Membrane Flippase in Plants. Biochemistry 2008; 47:10481-90. [DOI: 10.1021/bi8014339] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Santosh Kumar Sahu
- Department of Biotechnology, Indian Institute of Technology-Madras, Chennai 600 036, India
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25
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de Kruijff B, van Dam V, Breukink E. Lipid II: a central component in bacterial cell wall synthesis and a target for antibiotics. Prostaglandins Leukot Essent Fatty Acids 2008; 79:117-21. [PMID: 19008088 DOI: 10.1016/j.plefa.2008.09.020] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The bacterial cell wall is mainly composed of peptidoglycan, which is a three-dimensional network of long aminosugar strands located on the exterior of the cytoplasmic membrane. These strands consist of alternating MurNAc and GlcNAc units and are interlinked to each other via peptide moieties that are attached to the MurNAc residues. Peptidoglycan subunits are assembled on the cytoplasmic side of the bacterial membrane on a polyisoprenoid anchor and one of the key components in the synthesis of peptidoglycan is Lipid II. Being essential for bacterial cell survival, it forms an attractive target for antibacterial compounds such as vancomycin and several lantibiotics. Lipid II consists of one GlcNAc-MurNAc-pentapeptide subunit linked to a polyiosoprenoid anchor 11 subunits long via a pyrophosphate linker. This review focuses on this special molecule and addresses three questions. First, why are special lipid carriers as polyprenols used in the assembly of peptidoglycan? Secondly, how is Lipid II translocated across the bacterial cytoplasmic membrane? And finally, how is Lipid II used as a receptor for lantibiotics to kill bacteria?
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Affiliation(s)
- Ben de Kruijff
- Chemical Biology and Organic Chemistry, Utrecht University, Padualaan 8, Utrecht, The Netherlands
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26
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Nelson AR, Borland L, Allbritton NL, Sims CE. Myristoyl-based transport of peptides into living cells. Biochemistry 2007; 46:14771-81. [PMID: 18044965 DOI: 10.1021/bi701295k] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Translocation of membrane-impermeant molecules to the interior of living cells is a necessity for many biochemical investigations. Myristoylation was studied as a means to introduce peptides into living cells. Uptake of a myristoylated, fluorescent peptide was efficient in the B lymphocyte cell line BA/F3. In contrast, this cell line was resistant to uptake of a cell-penetrating peptide derived from the TAT protein. In BA/F3 cells, membrane association was shown to be rapid, reaching a maximum within 30 min. Cellular uptake of the peptide lagged the membrane association but occurred within a similar time frame. Experiments performed at 37 versus 4 degrees C demonstrated profound temperature dependence in the cellular uptake of myristoylated cargo. Myristoylated peptides with either positive or negative charge were shown to load efficiently. In contrast to TAT-conjugated cargo, pyrenebutyrate did not enhance cellular uptake of the myristoylated peptide. The myristoylated peptide did not adversely affect cell viability at concentrations up to 100 muM. This assessment of myristoyl-based transport provides fundamental data needed in understanding the intracellular delivery of myristoylated peptide cargoes for cell-based biochemical studies.
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Affiliation(s)
- Allison R Nelson
- Department of Physiology and Biophysics, University of California, Irvine, California 92697, USA
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27
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Vehring S, Pakkiri L, Schröer A, Alder-Baerens N, Herrmann A, Menon AK, Pomorski T. Flip-flop of fluorescently labeled phospholipids in proteoliposomes reconstituted with Saccharomyces cerevisiae microsomal proteins. EUKARYOTIC CELL 2007; 6:1625-34. [PMID: 17616631 PMCID: PMC2043374 DOI: 10.1128/ec.00198-07] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A phospholipid flippase activity from the endoplasmic reticulum (ER) of the model organism Saccharomyces cerevisiae has been characterized and functionally reconstituted into proteoliposomes. Analysis of the transbilayer movement of acyl-7-nitrobenz-2-oxa-1,3-diazol-4-yl (acyl-NBD)-labeled phosphatidylcholine in yeast microsomes using a fluorescence stopped-flow back exchange assay revealed a rapid, ATP-independent flip-flop (half-time, <2 min). Proteoliposomes prepared from a Triton X-100 extract of yeast microsomal membranes were also capable of flipping NBD-labeled phospholipid analogues rapidly in an ATP-independent fashion. Flippase activity was sensitive to the protein modification reagents N-ethylmaleimide and diethylpyrocarbonate. Resolution of the Triton X-100 extract by velocity gradient centrifugation resulted in the identification of a approximately 4S protein fraction enriched in flippase activity as well as of other fractions where flippase activity was depleted or undetectable. We estimate that flippase activity is due to a protein(s) representing approximately 2% (wt/wt) of proteins in the Triton X-100 extract. These results indicate that specific proteins are required to facilitate ATP-independent phospholipid flip-flop in the ER and that their identification is feasible. The architecture of the ER protein translocon suggests that it could account for the flippase activity in the ER. We tested this hypothesis using microsomes prepared from a temperature-sensitive yeast mutant in which the major translocon component, Sec61p, was quantitatively depleted. We found that the protein translocon is not required for transbilayer movement of phospholipids across the ER. Our work defines yeast as a promising model system for future attempts to identify the ER phospholipid flippase and to test and purify candidate flippases.
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Affiliation(s)
- Stefanie Vehring
- Institute of Biology/Biophysics, Humboldt University of Berlin, Invalidenstr. 42, 10115 Berlin, Germany
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28
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Nakano M, Fukuda M, Kudo T, Endo H, Handa T. Determination of interbilayer and transbilayer lipid transfers by time-resolved small-angle neutron scattering. PHYSICAL REVIEW LETTERS 2007; 98:238101. [PMID: 17677937 DOI: 10.1103/physrevlett.98.238101] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2007] [Indexed: 05/05/2023]
Abstract
We applied a time-resolved small-angle neutron scattering technique to the vesicle system of dimyristoylphosphatidylcholine for the first time to determine lipid kinetics. The observed kinetics could be explicitly represented by a simple model that includes two independent kinetic parameters, i.e., the rates of transbilayer and interbilayer exchange. This technique is perfectly suited for the determination of lipid exchange kinetics in equilibrium and applicable to evaluation of the activity of the factors relevant to lipid migration, such as translocase and lipid transfer proteins.
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Affiliation(s)
- Minoru Nakano
- Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8501, Japan.
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29
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Sahu SK, Gummadi SN, Manoj N, Aradhyam GK. Phospholipid scramblases: An overview. Arch Biochem Biophys 2007; 462:103-14. [PMID: 17481571 DOI: 10.1016/j.abb.2007.04.002] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2007] [Revised: 03/30/2007] [Accepted: 04/01/2007] [Indexed: 12/23/2022]
Abstract
Phospholipid scramblases are a group of homologous proteins that are conserved in all eukaryotic organisms. They are believed to be involved in destroying plasma membrane phospholipid asymmetry at critical cellular events like cell activation, injury and apoptosis. However, a detailed mechanism of phospholipid scrambling still awaits a proper understanding. The most studied member of this family, phospholipid scramblase 1 (PLSCR1) (a 37kDa protein), is involved in rapid Ca2+ dependent transbilayer redistribution of plasma membrane phospholipids. Recently the function of PLSCR1 as a phospholipids translocator has been challenged and evidences suggest that PLSCR1 acts as signaling molecule. It has been shown to be involved in protein phosphorylation and as a potential activator of genes in response to interferon and other cytokines. Interferon induced rapid biosynthesis of PLSCR1 targets some of the protein into the nucleus, where it binds to the promoter region of inositol 1,4,5-triphosphate (IP3) receptor type 1 (IP3R1) gene and induces its expression. Palmitoylation of PLSCR1 acts as a switch, controlling its localization either to the PM or inside the nucleus. In the present review, we discuss the current understanding of PLSCR1 in relation to its trafficking, localization and signaling functions.
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Affiliation(s)
- Santosh Kumar Sahu
- Department of Biotechnology, Indian Institute of Technology Madras, Chennai, India
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30
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Papadopulos A, Vehring S, López-Montero I, Kutschenko L, Stöckl M, Devaux PF, Kozlov M, Pomorski T, Herrmann A. Flippase activity detected with unlabeled lipids by shape changes of giant unilamellar vesicles. J Biol Chem 2007; 282:15559-68. [PMID: 17369612 DOI: 10.1074/jbc.m604740200] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Transbilayer movement of phospholipids in biological membranes is mediated by energy-dependent and energy-independent flippases. Available methods for detection of flippase mediated transversal flip-flop are essentially based on spin-labeled or fluorescent lipid analogues. Here we demonstrate that shape change of giant unilamellar vesicles (GUVs) can be used as a new tool to study the occurrence and time scale of flippase-mediated transbilayer movement of unlabeled phospholipids. Insertion of lipids into the external leaflet created an area difference between the two leaflets that caused the formation of a bud-like structure. Under conditions of negligible flip-flop, the bud was stable. Upon reconstitution of the energy-independent flippase activity of the yeast endoplasmic reticulum into GUVs, the initial bud formation was reversible, and the shapes were recovered. This can be ascribed to a rapid flip-flop leading to relaxation of the monolayer area difference. Theoretical analysis of kinetics of shape changes provides self-consistent determination of the flip-flop rate and further kinetic parameters. Based on that analysis, the half-time of phospholipid flip-flop in the presence of endoplasmic reticulum proteins was found to be on the order of few minutes. In contrast, GUVs reconstituted with influenza virus protein formed stable buds. The results argue for the presence of specific membrane proteins mediating rapid flip-flop.
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Affiliation(s)
- Andreas Papadopulos
- Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Institut für Biologie/Biophysik, Invalidenstrasse 42, D-10115 Berlin, Germany
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31
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Abstract
The envelope of Gram-negative bacteria is composed of two distinct lipid membranes: an inner membrane and outer membrane. The outer membrane is an asymmetric bilayer with an inner leaflet of phospholipids and an outer leaflet of lipopolysaccharide. Most of the steps of lipid synthesis occur within the cytoplasmic compartment of the cell. Lipids must then be transported across the inner membrane and delivered to the outer membrane. These topological features combined with the ability to apply the tools of biochemistry and genetics make the Gram-negative envelope a fascinating model for the study of lipid trafficking. In addition, as lipopolysaccharide is essential for growth of most strains and is a potent inducer of the mammalian innate immune response via activation of Toll-like receptors, Gram-negative lipid transport is also a promising target for the development of novel antibacterial and anti-inflammatory compounds. This review focuses on recent developments in our understanding of lipid transport across the inner membrane and to the outer membrane of Gram-negative bacteria.
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Affiliation(s)
- William T Doerrler
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
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32
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Devaux PF, López-Montero I, Bryde S. Proteins involved in lipid translocation in eukaryotic cells. Chem Phys Lipids 2006; 141:119-32. [PMID: 16600198 DOI: 10.1016/j.chemphyslip.2006.02.007] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2005] [Accepted: 02/20/2006] [Indexed: 11/17/2022]
Abstract
Since the first discovery of ATP-dependent translocation of lipids in the human erythrocyte membrane in 1984, there has been much evidence of the existence of various ATPases translocating lipids in eukaryotic cell membranes. They include P-type ATPases involved in inwards lipid transport from the exoplasmic leaflet to the cytosolic leaflet and ABC proteins involved in outwards transport. There are also ATP-independent proteins that catalyze the passage of lipids in both directions. Five P-type ATPase involved in lipid transport have been genetically characterized in yeast cells, suggesting a pool of several proteins with partially redundant activities responsible for the regulation of lipid asymmetry. However, expression and purification of individual yeast proteins is still insufficient to allow reconstitution experiments in liposomes. In this review, we want to give an overview over current investigation efforts about the identification and purification of proteins that may be involved in lipid translocation.
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Affiliation(s)
- Philippe F Devaux
- Institut de Biologie Physico-Chimique, UMR CNRS 7099, Paris, France.
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33
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Alder-Baerens N, Lisman Q, Luong L, Pomorski T, Holthuis JCM. Loss of P4 ATPases Drs2p and Dnf3p disrupts aminophospholipid transport and asymmetry in yeast post-Golgi secretory vesicles. Mol Biol Cell 2006; 17:1632-42. [PMID: 16452632 PMCID: PMC1415292 DOI: 10.1091/mbc.e05-10-0912] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Eukaryotic plasma membranes generally display asymmetric lipid distributions with the aminophospholipids concentrated in the cytosolic leaflet. This arrangement is maintained by aminophospholipid translocases (APLTs) that use ATP hydrolysis to flip phosphatidylserine (PS) and phosphatidylethanolamine (PE) from the external to the cytosolic leaflet. The identity of APLTs has not been established, but prime candidates are members of the P4 subfamily of P-type ATPases. Removal of P4 ATPases Dnf1p and Dnf2p from budding yeast abolishes inward translocation of 6-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)aminocaproyl] (NBD)-labeled PS, PE, and phosphatidylcholine (PC) across the plasma membrane and causes cell surface exposure of endogenous PE. Here, we show that yeast post-Golgi secretory vesicles (SVs) contain a translocase activity that flips NBD-PS, NBD-PE, and NBD-PC to the cytosolic leaflet. This activity is independent of Dnf1p and Dnf2p but requires two other P4 ATPases, Drs2p and Dnf3p, that reside primarily in the trans-Golgi network. Moreover, SVs have an asymmetric PE arrangement that is lost upon removal of Drs2p and Dnf3p. Our results indicate that aminophospholipid asymmetry is created when membrane flows through the Golgi and that P4-ATPases are essential for this process.
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Affiliation(s)
- Nele Alder-Baerens
- Institute of Biology and Biophysics, Humboldt University Berlin, 10115 Berlin, Germany
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34
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Vishwakarma RA, Vehring S, Mehta A, Sinha A, Pomorski T, Herrmann A, Menon AK. New fluorescent probes reveal that flippase-mediated flip-flop of phosphatidylinositol across the endoplasmic reticulum membrane does not depend on the stereochemistry of the lipid. Org Biomol Chem 2005; 3:1275-83. [PMID: 15785818 DOI: 10.1039/b500300h] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Glycerophospholipid flip-flop across biogenic membranes such as the endoplasmic reticulum (ER) is a fundamental feature of membrane biogenesis. Flip-flop requires the activity of specific membrane proteins called flippases. These proteins have yet to be identified in biogenic membranes and the molecular basis of their action is unknown. It is generally believed that flippase-facilitated glycerophospholipid flip-flop across the ER is governed by the stereochemistry of the glycerolipid, but this important issue has not been resolved. Here we investigate whether the ER flippase stereochemically recognizes the glycerophospholipids that it transports. To address this question we selected phosphatidylinositol (PI), a biologically important molecule with chiral centres in both its myo-inositol headgroup and its glycerol-lipid tail. The flip-flop of PI across the ER has not been previously reported. We synthesized fluorescence-labeled forms of all four diastereoisomers of PI and evaluated their flipping in rat liver ER vesicles, as well as in flippase-containing proteoliposomes reconstituted from a detergent extract of ER. Our results show that the flippase is able to translocate all four PI isomers and that both glycerol isomers of PI flip-flop across the ER membrane at rates similar to that measured for fluorescence-labeled phosphatidylcholine. Our data have important implications for recent hypotheses concerning the evolution of distinct homochiral glycerophospholipid membranes during the speciation of archaea and bacteria/eukarya from a common cellular ancestor.
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Affiliation(s)
- Ram A Vishwakarma
- Bio-Organic Chemistry Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, 110067, India.
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Pohl A, Devaux PF, Herrmann A. Function of prokaryotic and eukaryotic ABC proteins in lipid transport. Biochim Biophys Acta Mol Cell Biol Lipids 2004; 1733:29-52. [PMID: 15749056 DOI: 10.1016/j.bbalip.2004.12.007] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2004] [Revised: 11/08/2004] [Accepted: 12/16/2004] [Indexed: 12/23/2022]
Abstract
ATP binding cassette (ABC) proteins of both eukaryotic and prokaryotic origins are implicated in the transport of lipids. In humans, members of the ABC protein families A, B, C, D and G are mutated in a number of lipid transport and metabolism disorders, such as Tangier disease, Stargardt syndrome, progressive familial intrahepatic cholestasis, pseudoxanthoma elasticum, adrenoleukodystrophy or sitosterolemia. Studies employing transfection, overexpression, reconstitution, deletion and inhibition indicate the transbilayer transport of endogenous lipids and their analogs by some of these proteins, modulating lipid transbilayer asymmetry. Other proteins appear to be involved in the exposure of specific lipids on the exoplasmic leaflet, allowing their uptake by acceptors and further transport to specific sites. Additionally, lipid transport by ABC proteins is currently being studied in non-human eukaryotes, e.g. in sea urchin, trypanosomatides, arabidopsis and yeast, as well as in prokaryotes such as Escherichia coli and Lactococcus lactis. Here, we review current information about the (putative) role of both pro- and eukaryotic ABC proteins in the various phenomena associated with lipid transport. Besides providing a better understanding of phenomena like lipid metabolism, circulation, multidrug resistance, hormonal processes, fertilization, vision and signalling, studies on pro- and eukaryotic ABC proteins might eventually enable us to put a name on some of the proteins mediating transbilayer lipid transport in various membranes of cells and organelles. It must be emphasized, however, that there are still many uncertainties concerning the functions and mechanisms of ABC proteins interacting with lipids. In particular, further purification and reconstitution experiments with an unambiguous role of ATP hydrolysis are needed to demonstrate a clear involvement of ABC proteins in lipid transbilayer asymmetry.
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Affiliation(s)
- Antje Pohl
- Humboldt-University Berlin, Institute of Biology, Invalidenstr. 42, D-10115 Berlin, Germany.
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Abstract
Phospholipids play multiple roles in bacterial cells. These are the establishment of the permeability barrier, provision of the environment for many enzyme and transporter proteins, and they influence membrane-related processes such as protein export and DNA replication. The lipid synthetic pathway also provides precursors for protein modification and for the synthesis of other molecules. This review concentrates on the phospholipid synthetic pathway and discusses recent data on the synthesis and function of phospholipids mainly in the bacterium Escherichia coli.
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Affiliation(s)
- John E Cronan
- Department of Microbiology, University of Illinois, Urbana, Illinois 61801, USA.
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Rick PD, Barr K, Sankaran K, Kajimura J, Rush JS, Waechter CJ. Evidence that the wzxE gene of Escherichia coli K-12 encodes a protein involved in the transbilayer movement of a trisaccharide-lipid intermediate in the assembly of enterobacterial common antigen. J Biol Chem 2003; 278:16534-42. [PMID: 12621029 DOI: 10.1074/jbc.m301750200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The assembly of many bacterial cell surface polysaccharides requires the transbilayer movement of polyisoprenoid-linked saccharide intermediates across the cytoplasmic membrane. It is generally believed that transverse diffusion of glycolipid intermediates is mediated by integral membrane proteins called translocases or "flippases." The bacterial genes proposed to encode these translocases have been collectively designated wzx genes. The wzxE gene of Escherichia coli K-12 has been implicated in the transbilayer movement of Fuc4NAc-ManNAcA-GlcNAc-P-P-undecaprenol (lipid III), the donor of the trisaccharide repeat unit in the biosynthesis of enterobacterial common antigen (ECA). Previous studies (Feldman, M. F., Marolda, C. L., Monteiro, M. A., Perry, M. B., Parodi, A. J., and Valvano, M. (1999) J. Biol. Chem. 274, 35129-35138) provided indirect evidence that the wzx(016) gene product of E. coli K-12 encoded a translocase capable of mediating the transbilayer movement of N-acetylglucosaminylpyrophosphorylundecaprenol (GlcNAc-P-P-Und), an early intermediate in the synthesis of ECA and many lipopolysaccharide O antigens. Therefore, genetic and biochemical studies were conducted to determine if the putative Wzx(O16) translocase was capable of mediating the transport of N-acetylglucosaminylpyrophosphorylnerol (GlcNAc-P-P-Ner), a water-soluble analogue of GlcNAc-P-P-Und. [(3)H]GlcNAc-P-P-Ner was transported into sealed, everted cytoplasmic membrane vesicles of E. coli K-12 as well as a deletion mutant lacking both the wzx(016) and wzxC genes. In contrast, [(3)H]GlcNAc-P-P-Ner was not transported into membrane vesicles prepared from a wzxE-null mutant, and metabolic radiolabeling experiments revealed the accumulation of lipid III in this mutant. The WzxE transport system exhibited substrate specificity by recognizing both a pyrophosphoryl-linked saccharide and an unsaturated alpha-isoprene unit in the carrier lipid. These results support the conclusion that the wzxE gene encodes a membrane protein involved in the transbilayer movement of lipid III in E. coli.
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Affiliation(s)
- Paul D Rick
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA.
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John K, Schreiber S, Kubelt J, Herrmann A, Müller P. Transbilayer movement of phospholipids at the main phase transition of lipid membranes: implications for rapid flip-flop in biological membranes. Biophys J 2002; 83:3315-23. [PMID: 12496099 PMCID: PMC1302407 DOI: 10.1016/s0006-3495(02)75332-0] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The transbilayer movement of fluorescent phospholipid analogs in liposomes was studied at the lipid phase transition of phospholipid membranes. Two NBD-labeled analogs were used, one bearing the fluorescent moiety at a short fatty acid chain in the sn-2 position (C(6)-NBD-PC) and one headgroup-labeled analog having two long fatty acyl chains (N-NBD-PE). The transbilayer redistribution of the analogs was assessed by a dithionite-based assay. We observed a drastic increase of the transbilayer movement of both analogs at the lipid phase transition of DPPC (T(c) = 41 degrees C) and DMPC (T(c) = 23 degrees C). The flip-flop of analogs was fast at the T(c) of DPPC with a half-time (t(1/2)) of ~6-10 min and even faster at the T(c) of DMPC with t(1/2) on the order of <2 min, as shown for C(6)-NBD-PC. Suppressing the phase transition by the addition of cholesterol, the rapid transbilayer movement was abolished. Molecular packing defects at the phase transition are assumed to be responsible for the rapid transbilayer movement. The relevance of those defects for understanding of the activity of flippases is discussed.
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Affiliation(s)
- Karin John
- Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Institut für Biologie, Invalidenstrasse 43, D-10115 Berlin, Germany
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Watkins WE, Menon AK. Reconstitution of phospholipid flippase activity from E. coli inner membrane: a test of the protein translocon as a candidate flippase. Biol Chem 2002; 383:1435-40. [PMID: 12437136 DOI: 10.1515/bc.2002.162] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Phospholipid flipping in biogenic membranes is a key feature of membrane bilayer assembly. Flipping is facilitated by proteinaceous transporters (flippases) that do not need metabolic energy to function. No flippase has yet been identified. The architecture of the E. coli protein translocon suggests that it could account for the flippase activity in the bacterial inner membrane. To test this possibility, we used E. coli cells depleted of SecYE or YidC to assay flipping in proteoliposomes reconstituted from detergent extracts of their inner membranes. We conclude that the protein translocon contributes minimally, if at all, to phospholipid flippase activity in the inner membrane.
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Affiliation(s)
- William E Watkins
- Department of Biochemistry, University of Wisconsin-Madison, 53706-1569, USA
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Gummadi SN, Menon AK. Transbilayer movement of dipalmitoylphosphatidylcholine in proteoliposomes reconstituted from detergent extracts of endoplasmic reticulum. Kinetics of transbilayer transport mediated by a single flippase and identification of protein fractions enriched in flippase activity. J Biol Chem 2002; 277:25337-43. [PMID: 12000768 DOI: 10.1074/jbc.m203809200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholipid translocation (flip-flop) across membrane bilayers is typically assessed via assays utilizing partially water-soluble phospholipid analogs as transport reporters. These assays have been used in previous work to show that phospholipid translocation in biogenic (self-synthesizing) membranes such as the endoplasmic reticulum is facilitated by specific membrane proteins (flippases). To extend these studies to natural phospholipids while providing a framework to guide the purification of a flippase, we now describe an assay to measure the transbilayer translocation of dipalmitoylphosphatidylcholine, a membrane-embedded phospholipid, in proteoliposomes generated from detergent-solubilized rat liver endoplasmic reticulum. Translocation was assayed using phospholipase A(2) under conditions where the vesicles were determined to be intact. Phospholipase A(2) rapidly hydrolyzed phospholipids in the outer leaflet of liposomes and proteoliposomes with a half-time of approximately 0.1 min. However, for flippase-containing proteoliposomes, the initial rapid hydrolysis phase was followed by a slower phase reflecting flippase-mediated translocation of phospholipids from the inner to the outer leaflet. The amplitude of the slow phase was decreased in trypsin-treated proteoliposomes. The kinetic characteristics of the slow phase were used to assess the rate of transbilayer equilibration of phospholipids. For 250-nm diameter vesicles containing a single flippase, the half-time was 3.3 min. Proportionate reductions in equilibration half-time were observed for preparations with a higher average number of flippases/vesicle. Preliminary purification steps indicated that flippase activity could be enriched approximately 15-fold by sequential adsorption of the detergent extract onto anion and cation exchange resins.
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