51
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Sarfati R, Dufresne ER. Long-range attraction of particles adhered to lipid vesicles. Phys Rev E 2016; 94:012604. [PMID: 27575176 DOI: 10.1103/physreve.94.012604] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Indexed: 01/18/2023]
Abstract
Many biological systems fold thin sheets of lipid membrane into complex three-dimensional structures. This microscopic origami is often mediated by the adsorption and self-assembly of proteins on a membrane. As a model system to study adsorption-mediated interactions, we study the collective behavior of micrometric particles adhered to a lipid vesicle. We estimate the colloidal interactions using a maximum likelihood analysis of particle trajectories. When the particles are highly wrapped by a tense membrane, we observe strong long-range attractions with a typical binding energy of 150k_{B}T and significant forces extending a few microns.
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Affiliation(s)
- Raphael Sarfati
- Department of Applied Physics and Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut 06511, USA
| | - Eric R Dufresne
- Department of Materials ETH Zürich, 8092 Zürich, Switzerland and School of Engineering and Applied Sciences, Yale University, New Haven, Connecticut 06511, USA
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52
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Noguchi H. Shape deformation of lipid membranes by banana-shaped protein rods: Comparison with isotropic inclusions and membrane rupture. Phys Rev E 2016; 93:052404. [PMID: 27300921 DOI: 10.1103/physreve.93.052404] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Indexed: 06/06/2023]
Abstract
The assembly of curved protein rods on fluid membranes is studied using implicit-solvent meshless membrane simulations. As the rod curvature increases, the rods on a membrane tube assemble along the azimuthal direction first and subsequently along the longitudinal direction. Here, we show that both transition curvatures decrease with increasing rod stiffness. For comparison, curvature-inducing isotropic inclusions are also simulated. When the isotropic inclusions have the same bending rigidity as the other membrane regions, the inclusions are uniformly distributed on the membrane tubes and vesicles even for large spontaneous curvature of the inclusions. However, the isotropic inclusions with much larger bending rigidity induce shape deformation and are concentrated on the region of a preferred curvature. For high rod density, high rod stiffness, and/or low line tension of the membrane edge, the rod assembly induces vesicle rupture, resulting in the formation of a high-genus vesicle. A gradual change in the curvature suppresses this rupture. Hence, large stress, compared to the edge tension, induced by the rod assembly is the key factor determining rupture. For rod curvature with the opposite sign to the vesicle curvature, membrane rupture induces inversion of the membrane, leading to division into multiple vesicles as well as formation of a high-genus vesicle.
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Affiliation(s)
- Hiroshi Noguchi
- Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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53
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Abstract
I-BAR proteins are well-known actin-cytoskeleton adaptors and have been observed to be involved in the formation of plasma membrane protrusions (filopodia). I-BAR proteins contain an all-helical, crescent-shaped IRSp53-MIM domain (IMD) dimer that is believed to be able to couple with a membrane shape. This coupling could involve the sensing and even the generation of negative plasma membrane curvature. Indeed, the in vitro studies have shown that IMDs can induce inward tubulation of liposomes. While N-BAR domains, which generate positive membrane curvature, have received a considerable amount of attention from both theory and experiments, the mechanisms of curvature coupling through IMDs are comparatively less studied and understood. Here we used a membrane-shape stability assay developed recently in our lab to quantitatively characterize IMD-induced membrane-shape transitions. We determined a membrane-shape stability diagram for IMDs that reveals how membrane tension and protein density can comodulate the generation of IMD-induced membrane protrusions. From comparison to analytical theory, we determine three key parameters that characterize the curvature coupling of IMD. We find that the curvature generation capacity of IMDs is significantly stronger compared to that of endophilin, an N-BAR protein known to be involved in plasma membrane shape transitions. Contrary to N-BAR domains, where amphipathic helix insertion is known to promote its membrane curvature generation, for IMDs we find that amphipathic helices inhibit membrane shape transitions, consistent with the inverse curvature that IMDs generate. Importantly, in both of these types of BAR domains, electrostatic interactions affect membrane-binding capacity, but do not appear to affect the curvature generation capacity of the protein. These two types of BAR domain proteins show qualitatively similar membrane shape stability diagrams, suggesting an underlying ubiquitous mechanism by which peripheral proteins regulate membrane curvature.
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54
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Hutchison JB, Karunanayake Mudiyanselage APKK, Weis RM, Dinsmore AD. Osmotically-induced tension and the binding of N-BAR protein to lipid vesicles. SOFT MATTER 2016; 12:2465-2472. [PMID: 26822233 DOI: 10.1039/c5sm02496j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The binding affinity of a curvature-sensing protein domain (N-BAR) is measured as a function of applied osmotic stress while the membrane curvature is nearly constant. Varying the osmotic stress allows us to control membrane tension, which provides a probe of the mechanism of binding. We study the N-BAR domain of the Drosophila amphiphysin and monitor its binding on 50 nm-radius vesicles composed of 90 mol% DOPC and 10 mol% PIP. We find that the bound fraction of N-BAR is enhanced by a factor of approximately 6.5 when the tension increases from zero to 2.6 mN m(-1). This tension-induced response can be explained by the hydrophobic insertion mechanism. From the data we extract a hydrophobic domain area that is consistent with known structure. These results indicate that membrane stress and strain could play a major role in the previously reported curvature-affinity of N-BAR.
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Affiliation(s)
- Jaime B Hutchison
- Department of Physics, University of Massachusetts Amherst, Hasbrouck Lab 411, 666 North Pleasant Street, Amherst, MA 01003, USA.
| | | | - Robert M Weis
- Department of Chemistry, University of Massachusetts Amherst, USA
| | - Anthony D Dinsmore
- Department of Physics, University of Massachusetts Amherst, Hasbrouck Lab 411, 666 North Pleasant Street, Amherst, MA 01003, USA.
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55
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Membrane tubule formation by banana-shaped proteins with or without transient network structure. Sci Rep 2016; 6:20935. [PMID: 26863901 PMCID: PMC4750063 DOI: 10.1038/srep20935] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 01/13/2016] [Indexed: 11/08/2022] Open
Abstract
In living cells, membrane morphology is regulated by various proteins. Many membrane reshaping proteins contain a Bin/Amphiphysin/Rvs (BAR) domain, which consists of a banana-shaped rod. The BAR domain bends the biomembrane along the rod axis and the features of this anisotropic bending have recently been studied. Here, we report on the role of the BAR protein rods in inducing membrane tubulation, using large-scale coarse-grained simulations. We reveal that a small spontaneous side curvature perpendicular to the rod can drastically alter the tubulation dynamics at high protein density, whereas no significant difference is obtained at low density. A percolated network is intermediately formed depending on the side curvature. This network suppresses tubule protrusion, leading to the slow formation of fewer tubules. Thus, the side curvature, which is generated by protein–protein and membrane–protein interactions, plays a significant role in tubulation dynamics. We also find that positive surface tensions and the vesicle membrane curvature can stabilize this network structure by suppressing the tubulation.
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56
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Liu Y, Agudo-Canalejo J, Grafmüller A, Dimova R, Lipowsky R. Patterns of Flexible Nanotubes Formed by Liquid-Ordered and Liquid-Disordered Membranes. ACS NANO 2016; 10:463-74. [PMID: 26588094 DOI: 10.1021/acsnano.5b05377] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Biological membranes form both intra- and intercellular nanotubes that are used for molecular sorting within single cells and for long-distance connections between different cells. Such nanotubes can also develop from synthetic lipid bilayers in their fluid state. Each nanotube has a large area-to-volume ratio and stably encloses a water channel that is thereby shielded from its surroundings. The tubes are rather flexible and can easily change both their length and their conformation. Here, we study nanotubes formed by liquid-ordered (Lo) and liquid-disordered (Ld) membranes with three lipid components exposed to aqueous mixtures of two polymers, polyethylene glycol (PEG) and dextran. Both types of membranes form striking patterns of nanotubes when we reduce the volume of giant vesicles by osmotic deflation, thereby exposing the two bilayer leaflets of the membranes to polymer solutions of different composition. With decreasing volume, three different patterns are observed corresponding to three distinct vesicle morphologies that reflect the interplay of spontaneous curvature and aqueous phase separation. We show that tube nucleation and growth is governed by two kinetic pathways and that the tubes undergo a novel shape transformation from necklace-like to cylindrical tubes at a certain critical tube length. We deduce the spontaneous curvature generated by the membrane-polymer interactions from the observed vesicle morphologies using three different and independent methods of image analysis. The spontaneous curvature of the Ld membranes is found to be 4.7 times larger than that of the Lo membranes. We also show that these curvatures are generated by weak PEG adsorption onto the membranes, with a binding affinity of about 1.6 kBT per chain. In this way, our study provides a direct connection between nanoscopic membrane shapes and molecular interactions. Our approach is rather general and can be applied to many other systems of interest such as polymersomes or membrane-bound proteins and peptides.
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Affiliation(s)
- Yonggang Liu
- Theory & Biosystems, Max Planck Institute of Colloids and Interfaces , 14424 Potsdam, Germany
- State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , 130022 Changchun, China
| | - Jaime Agudo-Canalejo
- Theory & Biosystems, Max Planck Institute of Colloids and Interfaces , 14424 Potsdam, Germany
| | - Andrea Grafmüller
- Theory & Biosystems, Max Planck Institute of Colloids and Interfaces , 14424 Potsdam, Germany
| | - Rumiana Dimova
- Theory & Biosystems, Max Planck Institute of Colloids and Interfaces , 14424 Potsdam, Germany
| | - Reinhard Lipowsky
- Theory & Biosystems, Max Planck Institute of Colloids and Interfaces , 14424 Potsdam, Germany
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57
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Noguchi H. Formation of polyhedral vesicles and polygonal membrane tubes induced by banana-shaped proteins. J Chem Phys 2015; 143:243109. [DOI: 10.1063/1.4931896] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
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58
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Simunovic M, Voth GA, Callan-Jones A, Bassereau P. When Physics Takes Over: BAR Proteins and Membrane Curvature. Trends Cell Biol 2015; 25:780-792. [PMID: 26519988 DOI: 10.1016/j.tcb.2015.09.005] [Citation(s) in RCA: 193] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 09/08/2015] [Accepted: 09/14/2015] [Indexed: 10/22/2022]
Abstract
Cell membranes become highly curved during membrane trafficking, cytokinesis, infection, immune response, or cell motion. Bin/amphiphysin/Rvs (BAR) domain proteins with their intrinsically curved and anisotropic shape are involved in many of these processes, but with a large spectrum of modes of action. In vitro experiments and multiscale computer simulations have contributed in identifying a minimal set of physical parameters, namely protein density on the membrane, membrane tension, and membrane shape, that control how bound BAR domain proteins behave on the membrane. In this review, we summarize the multifaceted coupling of BAR proteins to membrane mechanics and propose a simple phase diagram that recapitulates the effects of these parameters.
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Affiliation(s)
- Mijo Simunovic
- Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute and Computation Institute, The University of Chicago, 5735 S Ellis Avenue, Chicago, IL 60637, USA; Institut Curie, Centre de Recherche, F-75248 Paris, France
| | - Gregory A Voth
- Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute and Computation Institute, The University of Chicago, 5735 S Ellis Avenue, Chicago, IL 60637, USA
| | - Andrew Callan-Jones
- Université Paris Diderot, F-75205 Paris, France; CNRS, Matière et Systèmes Complexes, UMR 7057, F-75205 Paris, France
| | - Patricia Bassereau
- Institut Curie, Centre de Recherche, F-75248 Paris, France; CNRS, PhysicoChimie Curie, UMR 168, F-75248 Paris, France; Université Pierre et Marie Curie, F-75252 Paris, France.
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59
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Prévost C, Zhao H, Manzi J, Lemichez E, Lappalainen P, Callan-Jones A, Bassereau P. IRSp53 senses negative membrane curvature and phase separates along membrane tubules. Nat Commun 2015; 6:8529. [PMID: 26469246 PMCID: PMC4634128 DOI: 10.1038/ncomms9529] [Citation(s) in RCA: 141] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 08/30/2015] [Indexed: 02/03/2023] Open
Abstract
BAR domain proteins contribute to membrane deformation in diverse cellular processes. The inverted-BAR (I-BAR) protein IRSp53, for instance, is found on the inner leaflet of the tubular membrane of filopodia; however its role in the formation of these structures is incompletely understood. Here we develop an original assay in which proteins are encapsulated in giant unilamellar vesicles connected to membrane nanotubes. Our results demonstrate that I-BAR dimers sense negative membrane curvature. Experiment and theory reveal that the I-BAR displays a non-monotonic sorting with curvature, and expands the tube at high imposed tension while constricting it at low tension. Strikingly, at low protein density and tension, protein-rich domains appear along the tube. This peculiar behaviour is due to the shallow intrinsic curvature of I-BAR dimers. It allows constriction of weakly curved membranes coupled to local protein enrichment at biologically relevant conditions. This might explain how IRSp53 contributes in vivo to the initiation of filopodia. The inverted-BAR domain protein IRSp53 associates with the inner leaflet of tubular membranes such as filopodia. Here, Prévost et al. demonstrate that the I-BAR domain of IRSp53 senses negative membrane curvature, and undergoes phase separation which may aid its clustering upon filopodia generation.
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Affiliation(s)
- Coline Prévost
- Institut Curie, Centre de Recherche, 75248 Paris Cedex 05, France.,CNRS, Physico-Chimie Curie, UMR 168, 75248 Paris Cedex 05, France.,Université Pierre et Marie Curie, 75252 Paris Cedex 05, France.,Université Paris-Diderot, 75205 Paris Cedex 05, France
| | - Hongxia Zhao
- Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - John Manzi
- Institut Curie, Centre de Recherche, 75248 Paris Cedex 05, France.,CNRS, Physico-Chimie Curie, UMR 168, 75248 Paris Cedex 05, France.,Université Pierre et Marie Curie, 75252 Paris Cedex 05, France
| | - Emmanuel Lemichez
- INSERM, U1065, UNSA, Centre Méditerranéen de Médecine Moléculaire, C3M, 06204 Nice Cedex 3, France
| | - Pekka Lappalainen
- Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - Andrew Callan-Jones
- CNRS, Laboratoire Matière et Systèmes Complexes, UMR 7057, 75205 Paris Cedex 13, France.,Université Paris-Diderot, 75205 Paris Cedex 05, France
| | - Patricia Bassereau
- Institut Curie, Centre de Recherche, 75248 Paris Cedex 05, France.,CNRS, Physico-Chimie Curie, UMR 168, 75248 Paris Cedex 05, France.,Université Pierre et Marie Curie, 75252 Paris Cedex 05, France
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60
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Rangamani P, Mandadap KK, Oster G. Protein-induced membrane curvature alters local membrane tension. Biophys J 2015; 107:751-762. [PMID: 25099814 DOI: 10.1016/j.bpj.2014.06.010] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 06/01/2014] [Accepted: 06/09/2014] [Indexed: 10/24/2022] Open
Abstract
Adsorption of proteins onto membranes can alter the local membrane curvature. This phenomenon has been observed in biological processes such as endocytosis, tubulation, and vesiculation. However, it is not clear how the local surface properties of the membrane, such as membrane tension, change in response to protein adsorption. In this article, we show that the partial differential equations arising from classical elastic model of lipid membranes, which account for simultaneous changes in shape and membrane tension due to protein adsorption in a local region, cannot be solved for nonaxisymmetric geometries using straightforward numerical techniques; instead, a viscous-elastic formulation is necessary to fully describe the system. Therefore, we develop a viscous-elastic model for inhomogeneous membranes of the Helfrich type. Using the newly available viscous-elastic model, we find that the lipids flow to accommodate changes in membrane curvature during protein adsorption. We show that, at the end of protein adsorption process, the system sustains a residual local tension to balance the difference between the actual mean curvature and the imposed spontaneous curvature. We also show that this change in membrane tension can have a functional impact such as altered response to pulling forces in the presence of proteins.
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Affiliation(s)
- Padmini Rangamani
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California
| | - Kranthi K Mandadap
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California; Department of Chemistry, University of California at Berkeley, Berkeley, California
| | - George Oster
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California.
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61
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Hilaire MR, Abaskharon RM, Gai F. Biomolecular Crowding Arising from Small Molecules, Molecular Constraints, Surface Packing, and Nano-Confinement. J Phys Chem Lett 2015; 6:2546-53. [PMID: 26266732 PMCID: PMC4610718 DOI: 10.1021/acs.jpclett.5b00957] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The effect of macromolecular crowding on the structure, dynamics, and reactivity of biomolecules is well established and the relevant research has been extensively reviewed. Herein, we focus our discussion on crowding effects arising from small cosolvent molecules and densely packed surface conditions. In addition, we highlight recent efforts that capitalize on the excluded volume effect for various tailored biochemical and biophysical applications. Specifically, we discuss how a targeted increase in local mass density can be exploited to gain insight into the folding dynamics of the protein of interest and how confinement via reverse micelles can be used to study a range of biophysical questions, from protein hydration dynamics to amyloid formation.
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Affiliation(s)
| | | | - Feng Gai
- To whom correspondence should be addressed; ; Phone: 215-573-6256; Fax: 215-573-2112
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62
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Svetina S. Curvature-dependent protein–lipid bilayer interaction and cell mechanosensitivity. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2015; 44:513-9. [DOI: 10.1007/s00249-015-1046-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Revised: 05/13/2015] [Accepted: 05/14/2015] [Indexed: 05/28/2023]
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63
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Tubulation by amphiphysin requires concentration-dependent switching from wedging to scaffolding. Structure 2015; 23:873-881. [PMID: 25865245 DOI: 10.1016/j.str.2015.02.014] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Revised: 02/09/2015] [Accepted: 02/24/2015] [Indexed: 02/08/2023]
Abstract
BAR proteins are involved in a variety of membrane remodeling events but how they can mold membranes into different shapes remains poorly understood. Using electron paramagnetic resonance, we find that vesicle binding of the N-BAR protein amphiphysin is predominantly mediated by the shallow insertion of amphipathic N-terminal helices. In contrast, the interaction with tubes involves deeply inserted N-terminal helices together with the concave surface of the BAR domain, which acts as a scaffold. Combined with the observed concentration dependence of tubulation and BAR domain scaffolding, the data indicate that initial membrane deformations and vesicle binding are mediated by insertion of amphipathic helical wedges, while tubulation requires high protein densities at which oligomeric BAR domain scaffolds form. In addition, we identify a pocket of residues on the concave surface of the BAR domain that insert deeply into tube membrane. Interestingly, this pocket harbors a number of disease mutants in the homologous amphiphysin 2.
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64
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Božič B, Das SL, Svetina S. Sorting of integral membrane proteins mediated by curvature-dependent protein-lipid bilayer interaction. SOFT MATTER 2015; 11:2479-2487. [PMID: 25675862 DOI: 10.1039/c4sm02289k] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Cell membrane proteins, both bound and integral, are known to preferentially accumulate at membrane locations with curvatures favorable to their shape. This is mainly due to the curvature dependent interaction between membrane proteins and their lipid environment. Here, we analyze the effects of the protein-lipid bilayer interaction energy due to mismatch between the protein shape and the principal curvatures of the surrounding bilayer. The role of different macroscopic parameters that define the interaction energy term is elucidated in relation to recent experiment in which the lateral distribution of a membrane embedded protein potassium channel KvAP is measured on a giant unilamellar lipid vesicle (reservoir) and a narrow tubular extension - a tether - kept at constant length. The dependence of the sorting ratio, defined as the ratio between the areal density of the protein on the tether and on the vesicle, on the inverse tether radius is influenced by the strength of the interaction, the intrinsic shape of the membrane embedded protein, and its abundance in the reservoir. It is described how the values of these constants can be extracted from experiments. The intrinsic principal curvatures of a protein are related to the tether radius at which the sorting ratio attains its maximum value. The estimate of the principal intrinsic curvature of the protein KvAP, obtained by comparing the experimental and theoretical sorting behavior, is consistent with the available information on its structure.
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Affiliation(s)
- Bojan Božič
- Institute of Biophysics, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
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65
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Wasnik V, Wingreen NS, Mukhopadhyay R. Modeling curvature-dependent subcellular localization of the small sporulation protein SpoVM in Bacillus subtilis. PLoS One 2015; 10:e0111971. [PMID: 25625300 PMCID: PMC4307972 DOI: 10.1371/journal.pone.0111971] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Accepted: 10/01/2014] [Indexed: 11/19/2022] Open
Abstract
Recent in vivo experiments suggest that in the bacterium, Bacillus subtilis, the cue for the localization of the small sporulation protein, SpoVM, an essential factor in spore coat formation, is curvature of the bacterial plasma membrane. In vitro measurements of SpoVM adsorption to vesicles of varying sizes also find high sensitivity of adsorption to vesicle radius. This curvature-dependent adsorption is puzzling given the orders of magnitude difference in length scale between an individual protein and the radius of curvature of the cell or vesicle, suggesting protein clustering on the membrane. Here we develop a minimal model to study the relationship between curvature-dependent membrane adsorption and clustering of SpoVM. Based on our analysis, we hypothesize that the radius dependence of SpoVM adsorption observed in vitro is governed primarily by membrane tension, while for in-vivo localization of SpoVM, we propose a highly sensitive mechanism for curvature sensing based on the formation of macroscopic protein clusters on the membrane.
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Affiliation(s)
- Vaibhav Wasnik
- Department of Physics, Clark University, Worcester, Massachusetts, United States of America
| | - Ned S. Wingreen
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Ranjan Mukhopadhyay
- Department of Physics, Clark University, Worcester, Massachusetts, United States of America
- * E-mail:
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66
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Simunovic M, Bassereau P. Reshaping biological membranes in endocytosis: crossing the configurational space of membrane-protein interactions. Biol Chem 2015; 395:275-83. [PMID: 24353142 DOI: 10.1515/hsz-2013-0242] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Accepted: 12/16/2013] [Indexed: 11/15/2022]
Abstract
Lipid membranes are highly dynamic. Over several decades, physicists and biologists have uncovered a number of ways they can change the shape of membranes or alter their phase behavior. In cells, the intricate action of membrane proteins drives these processes. Considering the highly complex ways proteins interact with biological membranes, molecular mechanisms of membrane remodeling still remain unclear. When studying membrane remodeling phenomena, researchers often observe different results, leading them to disparate conclusions on the physiological course of such processes. Here we discuss how combining research methodologies and various experimental conditions contributes to the understanding of the entire phase space of membrane-protein interactions. Using the example of clathrin-mediated endocytosis we try to distinguish the question 'how can proteins remodel the membrane?' from 'how do proteins remodel the membrane in the cell?' In particular, we consider how altering physical parameters may affect the way membrane is remodeled. Uncovering the full range of physical conditions under which membrane phenomena take place is key in understanding the way cells take advantage of membrane properties in carrying out their vital tasks.
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67
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Lipowsky R. Remodeling of membrane compartments: some consequences of membrane fluidity. Biol Chem 2015; 395:253-74. [PMID: 24491948 DOI: 10.1515/hsz-2013-0244] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Accepted: 11/30/2013] [Indexed: 01/16/2023]
Abstract
Biological membranes consist of fluid bilayers with many lipid and protein components. This fluidity implies a high flexibility that allows the membranes to attain a large variety of different shapes. One important shape parameter is the spontaneous curvature, which describes the asymmetry between the two leaflets of a bilayer and can be changed by adsorption of 'particles' such as ions or proteins from the aqueous phases. Membrane fluidity also implies that the membranes can change their local composition via lateral diffusion and form intramembrane compartments. Two mechanisms for the formation of such compartments can be distinguished: membrane segmentation arising from structured environments and domain formation as a result of phase separation within the membranes. The interplay between these two mechanisms provides a simple and generic explanation for the difficulty to observe phase domains in vivo. Intramembrane domains can form new membrane compartments via budding and tubulation processes. Which of these two processes actually occurs depends on the fluid-elastic properties of the domains, on the adsorption kinetics, and on external constraints arising, e.g., from the osmotic conditions. Vesicles are predicted to unbind from adhesive surfaces via tubulation when the spontaneous curvature of their membranes exceeds a certain threshold value.
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68
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Shi Z, Baumgart T. Membrane tension and peripheral protein density mediate membrane shape transitions. Nat Commun 2015; 6:5974. [PMID: 25569184 PMCID: PMC4353700 DOI: 10.1038/ncomms6974] [Citation(s) in RCA: 152] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Accepted: 11/28/2014] [Indexed: 01/21/2023] Open
Abstract
Endocytosis is a ubiquitous eukaryotic membrane budding, vesiculation and internalization process fulfilling numerous roles including compensation of membrane area increase after bursts of exocytosis. The mechanism of the coupling between these two processes to enable homeostasis is not well understood. Recently, an ultrafast endocytosis (UFE) pathway was revealed with a speed significantly exceeding classical clathrin-mediated endocytosis (CME). Membrane tension reduction is a potential mechanism by which endocytosis can be rapidly activated at remote sites. Here, we provide experimental evidence for a mechanism whereby membrane tension reduction initiates membrane budding and tubulation mediated by endocytic proteins, such as endophilin A1. We find that shape instabilities occur at well-defined membrane tensions and surface densities of endophilin. From our data, we obtain a membrane shape stability diagram that shows remarkable consistency with a quantitative model. This model applies to all laterally diffusive curvature-coupling proteins and therefore a wide range of endocytic proteins.
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Affiliation(s)
- Zheng Shi
- Department of Chemistry, University of Pennsylvania, 231 S. 34th St., Philadelphia, PA 19104, USA
| | - Tobias Baumgart
- Department of Chemistry, University of Pennsylvania, 231 S. 34th St., Philadelphia, PA 19104, USA
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69
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Beales PA, Ciani B, Cleasby AJ. Nature's lessons in design: nanomachines to scaffold, remodel and shape membrane compartments. Phys Chem Chem Phys 2015; 17:15489-507. [DOI: 10.1039/c5cp00480b] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Our understanding of the membrane sculpting capabilities of proteins from experimental model systems could be used to construct functional compartmentalised architectures for the engineering of synthetic cells.
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Affiliation(s)
- Paul A. Beales
- School of Chemistry and Astbury Centre for Structural Molecular Biology
- University of Leeds
- Leeds LS2 9JT
- UK
| | - Barbara Ciani
- Centre for Membrane Interaction and Dynamics
- Department of Chemistry
- University of Sheffield
- Sheffield S3 7HF
- UK
| | - Alexa J. Cleasby
- Centre for Membrane Interaction and Dynamics
- Department of Chemistry
- University of Sheffield
- Sheffield S3 7HF
- UK
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70
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Compeer EB, Boes M. MICAL-L1-related and unrelated mechanisms underlying elongated tubular endosomal network (ETEN) in human dendritic cells. Commun Integr Biol 2014; 7:e994969. [PMID: 26478765 PMCID: PMC4594581 DOI: 10.4161/19420889.2014.994969] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 07/29/2014] [Indexed: 01/03/2023] Open
Abstract
The endosomal pathway constitutes a highly dynamic intracellular transport system, which is composed of vesicular and tubular compartments. Endosomal tubules enable geometry-based discrimination between membrane and luminal content. Extended tubular endosomes were suggested to deliver a steady stream of membrane proteins to one location more reliable and effective than vesicular endosomes. Recently, we demonstrated that human dendritic cells (DCs) form a large elongated tubular endosomal network, e.g. ETEN, upon distinct triggers. LPS-stimulation triggered late endosomal tubulation. Additional clustering of class I MHC and ICAM-1 by a cognate interaction between antigen-laden DC and antigen-specific CD8+ T-cells induces formation of transferrin-positive tubules emanating from the endosomal recycling compartment (ERC). We here discuss cell-biological mechanisms that are involved in membrane bending and possibly underlie initiation, elongation, and stabilization of ETEN in human DCs. Using a knock-down approach we demonstrate that MICAL-L1 is necessary for ETEN remodeling originating from ERC in human DCs.
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Affiliation(s)
- Ewoud B Compeer
- Department of Pediatrics; Laboratory of Translational Immunology; University Medical Center Utrecht; Wilhelmina Children's Hospital ; Utrecht, The Netherlands
| | - Marianne Boes
- Department of Pediatrics; Laboratory of Translational Immunology; University Medical Center Utrecht; Wilhelmina Children's Hospital ; Utrecht, The Netherlands
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71
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Mahata P, Das SL. Two-dimensional convex-molecule fluid model for surface adsorption of proteins: effect of soft interaction on adsorption equilibria. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:062713. [PMID: 25615135 DOI: 10.1103/physreve.90.062713] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2014] [Indexed: 06/04/2023]
Abstract
Adsorption of proteins on membrane surfaces plays an important role in cell biological processes. In this work, we develop a two-dimensional fluid model for proteins. The protein molecules have been modeled as two-dimensional convex and soft particles. The Lennard-Jones potential for circular particles and Kihara (12,6) potential for elliptical particles with hard core have been used to model pairwise intermolecular interactions. The equation of state of the fluid model has been derived using Weeks-Chandler-Andersen decomposition and it involves three parameters, an attraction, a repulsion, and a size parameter, which depend on the shape and core size of the molecules. For validation of the model, a two-dimensional molecular dynamics simulation has been performed. Finally, the model has been applied to study the adsorption of proteins on a flat membrane. In comparison with the existing model of hard and convex particles for protein adsorption, our model predicts a higher packing fraction for the adsorption equilibria. Although the present work is based on Lennard-Jones-type interaction, it can be extended for other specific soft interactions between convex molecules. Thus the model has general applicability for any other two-dimensional adsorption systems of molecules with soft interaction.
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Affiliation(s)
- Paritosh Mahata
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Sovan Lal Das
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India
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72
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Wu T, Baumgart T. BIN1 membrane curvature sensing and generation show autoinhibition regulated by downstream ligands and PI(4,5)P2. Biochemistry 2014; 53:7297-309. [PMID: 25350771 PMCID: PMC4245986 DOI: 10.1021/bi501082r] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
In striated muscles, invaginations
from the plasma membrane, termed
transverse tubules (T-tubule), function in the excitation–contraction
coupling machinery. BIN1 (isoform8) plays a critical role in the biogenesis
of T-tubules. BIN1 contains an N-terminal BAR domain to sense and
induce membrane curvature, an isoform8-specific polybasic motif (exon10)
as the phosphoinositide binding module and a C-terminal Src homology
3 (SH3) domain for the recruitment of downstream proteins such as
dynamin 2. Previous studies of N-BAR domains focused on elucidating
mechanisms of membrane curvature sensing and generation (MC-S&G).
Less is known about how MC-S&G is regulated. We found that the
SH3 domain binds to the exon10 motif more strongly compared to the
proline-rich domain (PRD) of dynamin 2. Furthermore, we found that
the MC-S&G ability of full-length BIN1 is inhibited on membranes
lacking PI(4,5)P2. Addition of PI(4,5)P2 in
the membrane activates BIN1 to sense and induce membrane curvature.
Co-presence of the SH3 domain and exon10 motif leads to the strongest
phosphoinositide-mediated control of BIN1 function. Addition of SH3
domain ligand (such as PRD peptides), as well as addition of the water-soluble
PI(4,5)P2 analogue, can both enhance the MC-S&G ability
of BIN1 on membranes without PI(4,5)P2, indicating that
the key to activate BIN1 is to disrupt the exon10–SH3 interaction.
The nonsense mutation K436X, found in centronuclear myopathy (CNM)
patients, abolishes SH3 domain binding with either exon10 or the PRD
motif, resulting in increased membrane deformation capacity. Our results
suggest an autoinhibition model for BIN1 that involves a synergistic
regulation by membrane composition and protein–protein interactions.
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Affiliation(s)
- Tingting Wu
- Department of Chemistry, School of Arts & Sciences, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
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73
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Ramakrishnan N, Sunil Kumar PB, Radhakrishnan R. Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins. PHYSICS REPORTS 2014; 543:1-60. [PMID: 25484487 PMCID: PMC4251917 DOI: 10.1016/j.physrep.2014.05.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this description, the protein is expressed in the form of a spontaneous curvature field. The approaches include field theoretical methods limited to the small deformation regime, triangulated surfaces and particle-based computational models to investigate the large-deformation regimes observed in the natural state of many biological membranes. Applications of these methods to understand the properties of biological membranes in homogeneous and inhomogeneous environments of proteins, whose underlying curvature fields are either isotropic or anisotropic, are discussed. The diversity in the curvature fields elicits a rich variety of morphological states, including tubes, discs, branched tubes, and caveola. Mapping the thermodynamic stability of these states as a function of tuning parameters such as concentration and strength of curvature induction of the proteins is discussed. The relative stabilities of these self-organized shapes are examined through free-energy calculations. The suite of methods discussed here can be tailored to applications in specific cellular settings such as endocytosis during cargo trafficking and tubulation of filopodial structures in migrating cells, which makes these methods a powerful complement to experimental studies.
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Affiliation(s)
- N. Ramakrishnan
- Department of Chemical and Biomolecular Engineering, Department of Bioengineering, Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA-19104
| | - P. B. Sunil Kumar
- Department of Physics, Indian Institute of Technology Madras, Chennai, India - 600036
| | - Ravi Radhakrishnan
- Department of Chemical and Biomolecular Engineering, Department of Bioengineering, Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA-19104
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74
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Tourdot RW, Ramakrishnan N, Radhakrishnan R. Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:022717. [PMID: 25215768 PMCID: PMC4336182 DOI: 10.1103/physreve.90.022717] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Indexed: 05/08/2023]
Abstract
Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane-in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer membranes.
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Affiliation(s)
- Richard W. Tourdot
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - N. Ramakrishnan
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Ravi Radhakrishnan
- Department of Chemical and Biomolecular Engineering, Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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75
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Braun AR, Lacy MM, Ducas VC, Rhoades E, Sachs JN. α-Synuclein-induced membrane remodeling is driven by binding affinity, partition depth, and interleaflet order asymmetry. J Am Chem Soc 2014; 136:9962-72. [PMID: 24960410 PMCID: PMC4105054 DOI: 10.1021/ja5016958] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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We have investigated
the membrane remodeling capacity of the N-terminal
membrane-binding domain of α-synuclein (α-Syn100). Using fluorescence correlation spectroscopy and vesicle clearance
assays, we show that α-Syn100 fully tubulates POPG
vesicles, the first demonstration that the amphipathic helix on its
own is capable of this effect. We also show that at equal density
of membrane-bound protein, α-Syn has dramatically reduced affinity
for, and does not tubulate, vesicles composed of a 1:1 POPG:POPC mixture.
Coarse-grained molecular dynamics simulations suggested that the difference
between the pure POPG and mixture results may be attributed to differences
in the protein’s partition depth, the membrane’s hydrophobic
thickness, and disruption of acyl chain order. To explore the importance
of these attributes compared with the role of the reduced binding
energy, we created an α-Syn100 variant in which we
removed the hydrophobic core of the non-amyloid component (NAC) domain
and tested its impact on pure POPG vesicles. We observed a substantial
reduction in binding affinity and tubulation, and simulations of the
NAC-null protein suggested that the reduced binding energy increases
the protein mobility on the bilayer surface, likely impacting the
protein’s ability to assemble into organized pretubule structures.
We also used simulations to explore a potential role for interleaflet
coupling as an additional driving force for tubulation. We conclude
that symmetry across the leaflets in the tubulated state maximizes
the interaction energy of the two leaflets and relieves the strain
induced by the hydrophobic void beneath the amphipathic helix.
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Affiliation(s)
- Anthony R Braun
- Department of Biomedical Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States
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76
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Shen H, Giordano F, Wu Y, Chan J, Zhu C, Milosevic I, Wu X, Yao K, Chen B, Baumgart T, Sieburth D, De Camilli P. Coupling between endocytosis and sphingosine kinase 1 recruitment. Nat Cell Biol 2014; 16:652-62. [PMID: 24929359 PMCID: PMC4230894 DOI: 10.1038/ncb2987] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 05/09/2014] [Indexed: 12/13/2022]
Abstract
Genetic studies have suggested a functional link between cholesterol/sphingolipid metabolism and endocytic membrane traffic. Here we show that perturbing the cholesterol/sphingomyelin balance in the plasma membrane results in the massive formation of clusters of narrow endocytic tubular invaginations positive for N-BAR proteins. These tubules are intensely positive for sphingosine kinase 1 (SPHK1). SPHK1 is also targeted to physiologically occurring early endocytic intermediates, and is highly enriched in nerve terminals, which are cellular compartments specialized for exo/endocytosis. Membrane recruitment of SPHK1 involves a direct, curvature-sensitive interaction with the lipid bilayer mediated by a hydrophobic patch on the enzyme's surface. The knockdown of SPHKs results in endocytic recycling defects, and a mutation that disrupts the hydrophobic patch of Caenorhabditis elegans SPHK fails to rescue the neurotransmission defects in loss-of-function mutants of this enzyme. Our studies support a role for sphingosine phosphorylation in endocytic membrane trafficking beyond the established function of sphingosine-1-phosphate in intercellular signalling.
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Affiliation(s)
- Hongying Shen
- 1] Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, Connecticut 06510, USA [2] Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA [3]
| | - Francesca Giordano
- 1] Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, Connecticut 06510, USA [2] Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA [3]
| | - Yumei Wu
- 1] Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, Connecticut 06510, USA [2] Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Jason Chan
- 1] Zilkha Neurogenetic Institute, Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA [2]
| | - Chen Zhu
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Ira Milosevic
- 1] Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, Connecticut 06510, USA [2] Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Xudong Wu
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Kai Yao
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Bo Chen
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Tobias Baumgart
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Derek Sieburth
- Zilkha Neurogenetic Institute, Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA
| | - Pietro De Camilli
- 1] Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, Connecticut 06510, USA [2] Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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77
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Shi Z, Baumgart T. Dynamics and instabilities of lipid bilayer membrane shapes. Adv Colloid Interface Sci 2014; 208:76-88. [PMID: 24529968 DOI: 10.1016/j.cis.2014.01.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Revised: 01/12/2014] [Accepted: 01/12/2014] [Indexed: 01/14/2023]
Abstract
Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that describe the fluctuations (i.e. undulations) of bilayer shapes as well as their local coupling with lipid or protein density variation. The coupling between local membrane curvature and lipid density gives rise to a 'slipping mode' in addition to the conventional 'bending mode' for damping the membrane fluctuation. This leads to a number of interesting experimental phenomena regarding bilayer shape dynamics. More importantly, curvature-inducing proteins can couple with membrane shape and eventually render the membrane unstable. A criterion for membrane shape instability is derived from a linear stability analysis. The instability criterion reemphasizes the importance of membrane tension in regulating the stability and dynamics of membrane geometry. Recent progresses in understanding the role of membrane tension in regulating dynamical cellular processes are also reviewed. Protein density is emphasized as a key factor in regulating membrane shape transitions: a threshold density of curvature coupling proteins is required for inducing membrane morphology transitions.
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Affiliation(s)
- Zheng Shi
- Department of Chemistry, University of Pennsylvania, 231 S. 34th St., Philadelphia, PA 19104, USA
| | - Tobias Baumgart
- Department of Chemistry, University of Pennsylvania, 231 S. 34th St., Philadelphia, PA 19104, USA.
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78
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Bassereau P, Sorre B, Lévy A. Bending lipid membranes: experiments after W. Helfrich's model. Adv Colloid Interface Sci 2014; 208:47-57. [PMID: 24630341 DOI: 10.1016/j.cis.2014.02.002] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Revised: 02/02/2014] [Accepted: 02/03/2014] [Indexed: 10/25/2022]
Abstract
Current description of biomembrane mechanics originates for a large part from W. Helfrich's model. Based on his continuum theory, many experiments have been performed in the past four decades on simplified membranes in order to characterize the mechanical properties of lipid membranes and the contribution of polymers or proteins. The long-term goal was to develop a better understanding of the mechanical properties of cell membranes. In this paper, we will review representative experimental approaches that were developed during this period and the main results that were obtained.
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79
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Endophilin A1 induces different membrane shapes using a conformational switch that is regulated by phosphorylation. Proc Natl Acad Sci U S A 2014; 111:6982-7. [PMID: 24778241 DOI: 10.1073/pnas.1402233111] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Membrane remodeling is controlled by proteins that can promote the formation of highly curved spherical or cylindrical membranes. How a protein induces these different types of membrane curvature and how cells regulate this process is still unclear. Endophilin A1 is a protein involved in generating endocytotic necks and vesicles during synaptic endocytosis and can transform large vesicles into lipid tubes or small and highly curved vesicles in vitro. By using EM and electron paramagnetic resonance of endophilin A1, we find that tubes are formed by a close interaction with endophilin A1's BIN/amphiphysin/Rvs (BAR) domain and deep insertion of its amphipathic helices. In contrast, vesicles are predominantly stabilized by the shallow insertion of the amphipathic helical wedges with the BAR domain removed from the membrane. By showing that the mechanism of membrane curvature induction is different for vesiculation and tubulation, these data also explain why previous studies arrived at different conclusions with respect to the importance of scaffolding and wedging in the membrane curvature generation of BAR proteins. The Parkinson disease-associated kinase LRRK2 phosphorylates S75 of endophilin A1, a position located in the acyl chain region on tubes and the aqueous environment on vesicles. We find that the phosphomimetic mutation S75D favors vesicle formation by inhibiting this conformational switch, acting to regulate endophilin A1-mediated curvature. As endophilin A1 is part of a protein superfamily, we expect these mechanisms and their regulation by posttranslational modifications to be a general means for controlling different types of membrane curvature in a wide range of processes in vivo.
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80
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Wu T, Shi Z, Baumgart T. Mutations in BIN1 associated with centronuclear myopathy disrupt membrane remodeling by affecting protein density and oligomerization. PLoS One 2014; 9:e93060. [PMID: 24755653 PMCID: PMC3995651 DOI: 10.1371/journal.pone.0093060] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2013] [Accepted: 03/02/2014] [Indexed: 11/18/2022] Open
Abstract
The regulation of membrane shapes is central to many cellular phenomena. Bin/Amphiphysin/Rvs (BAR) domain-containing proteins are key players for membrane remodeling during endocytosis, cell migration, and endosomal sorting. BIN1, which contains an N-BAR domain, is assumed to be essential for biogenesis of plasma membrane invaginations (T-tubules) in muscle tissues. Three mutations, K35N, D151N and R154Q, have been discovered so far in the BAR domain of BIN1 in patients with centronuclear myopathy (CNM), where impaired organization of T-tubules has been reported. However, molecular mechanisms behind this malfunction have remained elusive. None of the BIN1 disease mutants displayed a significantly compromised curvature sensing ability. However, two mutants showed impaired membrane tubulation both in vivo and in vitro, and displayed characteristically different behaviors. R154Q generated smaller membrane curvature compared to WT N-BAR. Quantification of protein density on membranes revealed a lower membrane-bound density for R154Q compared to WT and the other mutants, which appeared to be the primary reason for the observation of impaired deformation capacity. The D151N mutant was unable to tubulate liposomes under certain experimental conditions. At medium protein concentrations we found 'budding' structures on liposomes that we hypothesized to be intermediates during the tubulation process except for the D151N mutant. Chemical crosslinking assays suggested that the D151N mutation impaired protein oligomerization upon membrane binding. Although we found an insignificant difference between WT and K35N N-BAR in in vitro assays, depolymerizing actin in live cells allowed tubulation of plasma membranes through the K35N mutant. Our results provide insights into the membrane-involved pathophysiological mechanisms leading to human disease.
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Affiliation(s)
- Tingting Wu
- Department of Chemistry, School of Arts & Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Zheng Shi
- Department of Chemistry, School of Arts & Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Tobias Baumgart
- Department of Chemistry, School of Arts & Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
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81
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Chen Z, Chang K, Capraro BR, Zhu C, Hsu CJ, Baumgart T. Intradimer/Intermolecular interactions suggest autoinhibition mechanism in endophilin A1. J Am Chem Soc 2014; 136:4557-64. [PMID: 24568626 PMCID: PMC3985530 DOI: 10.1021/ja411607b] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
![]()
Endophilin
A1 is a homodimeric membrane-binding endocytic accessory
protein with a high dimerization affinity. Its function has been hypothesized
to involve autoinhibition. However, the autoinhibition mechanism,
as well as the physicochemical basis for the high dimerization affinity
of endophilin in solution, have remained unclear. In this contribution,
we use a Förster resonance energy transfer (FRET) method to
investigate the homodimerization mechanism and intradimer molecular
interactions in endophilin. For the endophilin N-BAR domain (which
lacks the SH3 domain including a linker region of the full length
protein), we observe a large temperature dependence of the dimerization
affinity and dimer dissociation kinetics, implying large dimerization
enthalpy and dissociation activation enthalpy, respectively. Our evaluation
of the protein concentration dependence of dimer dissociation kinetics
implies that endophilin reversibly forms monomers via a dissociation/reassociation
mechanism. Furthermore, we use a kinetic method that allows us to
compare the dissociation kinetics of full-length endophilin to that
of truncated mutants. We find that mutants that lack either H0 helix
or SH3 domain show significantly faster dissociation kinetics relative
to full-length endophilin. This observation supports the presence
of an intradimer, intermonomer cross-interaction between H0 helix
and SH3 domain from different subunits within a homodimer. Because
the H0 helix is known to play a significant role in endophilin’s
membrane interactions, our measurements support a syngergistic model
where these interactions are inhibited in the absence of SH3 domain
binding ligands such as dynamin’s prolin rich domains, and
where the binding of these ligands may be suppressed for non-membrane-bound
endophilin.
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Affiliation(s)
- Zhiming Chen
- Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104, United States
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82
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Czogalla A, Grzybek M, Jones W, Coskun U. Validity and applicability of membrane model systems for studying interactions of peripheral membrane proteins with lipids. Biochim Biophys Acta Mol Cell Biol Lipids 2013; 1841:1049-59. [PMID: 24374254 DOI: 10.1016/j.bbalip.2013.12.012] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 12/12/2013] [Accepted: 12/17/2013] [Indexed: 12/11/2022]
Abstract
The cell membrane serves, at the same time, both as a barrier that segregates as well as a functional layer that facilitates selective communication. It is characterized as much by the complexity of its components as by the myriad of signaling process that it supports. And, herein lays the problems in its study and understanding of its behavior - it has a complex and dynamic nature that is further entangled by the fact that many events are both temporal and transient in their nature. Model membrane systems that bypass cellular complexity and compositional diversity have tremendously accelerated our understanding of the mechanisms and biological consequences of lipid-lipid and protein-lipid interactions. Concurrently, in some cases, the validity and applicability of model membrane systems are tarnished by inherent methodical limitations as well as undefined quality criteria. In this review we introduce membrane model systems widely used to study protein-lipid interactions in the context of key parameters of the membrane that govern lipid availability for peripheral membrane proteins. This article is part of a Special Issue entitled Tools to study lipid functions.
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Affiliation(s)
- Aleksander Czogalla
- Laboratory of Membrane Biochemistry, Paul Langerhans Institute Dresden, Faculty of Medicine Carl Gustav Carus at the TU Dresden, Fetscherstrasse 74, 01307 Dresden, Germany; German Center for Diabetes Research (DZD), Germany.
| | - Michał Grzybek
- Laboratory of Membrane Biochemistry, Paul Langerhans Institute Dresden, Faculty of Medicine Carl Gustav Carus at the TU Dresden, Fetscherstrasse 74, 01307 Dresden, Germany; German Center for Diabetes Research (DZD), Germany
| | - Walis Jones
- Laboratory of Membrane Biochemistry, Paul Langerhans Institute Dresden, Faculty of Medicine Carl Gustav Carus at the TU Dresden, Fetscherstrasse 74, 01307 Dresden, Germany; German Center for Diabetes Research (DZD), Germany
| | - Unal Coskun
- Laboratory of Membrane Biochemistry, Paul Langerhans Institute Dresden, Faculty of Medicine Carl Gustav Carus at the TU Dresden, Fetscherstrasse 74, 01307 Dresden, Germany; German Center for Diabetes Research (DZD), Germany.
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83
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Linear aggregation of proteins on the membrane as a prelude to membrane remodeling. Proc Natl Acad Sci U S A 2013; 110:20396-401. [PMID: 24284177 DOI: 10.1073/pnas.1309819110] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Adhesion and insertion of curvature-mediating proteins can induce dramatic structural changes in cell membranes, allowing them to participate in several key cellular tasks. The way proteins interact to generate curvature remains largely unclear, especially at early stages of membrane remodeling. Using a coarse-grained model of Bin/amphiphysin/Rvs domain with an N-terminal helix (N-BAR) interacting with flat membranes and vesicles, we demonstrate that at low protein surface densities, binding of N-BAR domain proteins to the membrane is followed by a linear aggregation and the formation of meshes on the surface. In this process, the proteins assemble at the base of emerging membrane buds. Our work shows that beyond a more straightforward scaffolding mechanism at high bound densities, the interplay of anisotropic interactions and the local stress imposed by the N-BAR proteins results in deep invaginations and endocytic vesicular bud-like deformations, an order of magnitude larger than the size of the individual protein. Our results imply that by virtue of this mechanism, cell membranes may achieve rapid local increases in protein concentration.
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84
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Sarkar N, Basu A. Phases and fluctuations in a model for asymmetric inhomogeneous fluid membranes. Phys Rev E 2013; 88:042106. [PMID: 24229115 DOI: 10.1103/physreve.88.042106] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Indexed: 01/25/2023]
Abstract
We propose and analyze a model for phase transitions in an inhomogeneous fluid membrane, that couples local composition with curvature nonlinearly. For asymmetric membranes, our model shows generic non-Ising behavior and the ensuing phase diagram displays either a first- or a second-order phase transition through a critical point (CP) or a tricritical point (TP), depending upon the bending modulus. It predicts generic nontrivial enhancement in fluctuations of asymmetric membranes that scales with system size in a power-law fashion at the CP and TP in two dimensions, not observed in symmetric membranes. It also yields two-dimensional Ising universality class for symmetric membranes, in agreement with experimental results.
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Affiliation(s)
- Niladri Sarkar
- Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Calcutta 700064, India
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85
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Poudel KR, Bai J. Synaptic vesicle morphology: a case of protein sorting? Curr Opin Cell Biol 2013; 26:28-33. [PMID: 24529243 DOI: 10.1016/j.ceb.2013.09.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 09/03/2013] [Accepted: 09/04/2013] [Indexed: 10/26/2022]
Abstract
Synaptic vesicles (SVs) are the repositories of neurotransmitters. They are locally recycled at nerve terminals following exocytosis. A unique feature of these vesicles is the uniformity of their morphology, which is well maintained even after rounds of exocytosis and endocytosis. Several studies suggest that disruption of clathrin adaptor proteins leads to defects in sorting cargoes and alterations in SV morphology. Here, we review the links between adaptor proteins and SV size, and highlight how protein sorting may impact SV architecture. Molecular players such as clathrin, adaptor proteins, accessory proteins, SV cargoes and lipid composition may act together to establish a stable regulatory network to maintain SV morphology.
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Affiliation(s)
- Kumud R Poudel
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA; Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - Jihong Bai
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA; Department of Biochemistry, University of Washington, Seattle, WA, USA.
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86
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Ramesh P, Baroji YF, Reihani SNS, Stamou D, Oddershede LB, Bendix PM. FBAR syndapin 1 recognizes and stabilizes highly curved tubular membranes in a concentration dependent manner. Sci Rep 2013; 3:1565. [PMID: 23535634 PMCID: PMC3610093 DOI: 10.1038/srep01565] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 03/14/2013] [Indexed: 12/21/2022] Open
Abstract
Syndapin 1 FBAR, a member of the Bin-amphiphysin-Rvs (BAR) domain protein family, is known to induce membrane curvature and is an essential component in biological processes like endocytosis and formation and growth of neurites. We quantify the curvature sensing of FBAR on reconstituted porcine brain lipid vesicles and show that it senses membrane curvature at low density whereas it induces and reinforces tube stiffness at higher density. FBAR strongly up-concentrates on the high curvature tubes pulled out of Giant Unilamellar lipid Vesicles (GUVs), this sorting behavior is strongly amplified at low protein densities. Interestingly, FBAR from syndapin 1 has a large affinity for tubular membranes with curvatures larger than its own intrinsic concave curvature. Finally, we studied the effect of FBAR on membrane relaxation kinetics with high temporal resolution and found that the protein increases relaxation time of the tube holding force in a density-dependent fashion.
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Affiliation(s)
- Pradeep Ramesh
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark
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87
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Capraro BR, Shi Z, Wu T, Chen Z, Dunn JM, Rhoades E, Baumgart T. Kinetics of endophilin N-BAR domain dimerization and membrane interactions. J Biol Chem 2013; 288:12533-43. [PMID: 23482561 DOI: 10.1074/jbc.m112.435511] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The recruitment to plasma membrane invaginations of the protein endophilin is a temporally regulated step in clathrin-mediated endocytosis. Endophilin is believed to sense or stabilize membrane curvature, which in turn likely depends on the dimeric structure of the protein. The dynamic nature of the membrane association and dimerization of endophilin is thus functionally important and is illuminated herein. Using subunit exchange Förster resonance energy transfer (FRET), we determine dimer dissociation kinetics and find a dimerization equilibrium constant orders of magnitude lower than previously published values. We characterize N-BAR domain membrane association kinetics under conditions where the dimeric species predominates, by stopped flow, observing prominent electrostatic sensitivity of membrane interaction kinetics. Relative to membrane binding, we find that protein monomer/dimer species equilibrate with far slower kinetics. Complementary optical microscopy studies reveal strikingly slow membrane dissociation and an increase of dissociation rate constant for a construct lacking the amphipathic segment helix 0 (H0). We attribute the slow dissociation kinetics to higher-order protein oligomerization on the membrane. We incorporate our findings into a kinetic scheme for endophilin N-BAR membrane binding and find a significant separation of time scales for endophilin membrane binding and subsequent oligomerization. This separation may facilitate the regulation of membrane trafficking phenomena.
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Affiliation(s)
- Benjamin R Capraro
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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88
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Bigay J, Antonny B. Curvature, lipid packing, and electrostatics of membrane organelles: defining cellular territories in determining specificity. Dev Cell 2013; 23:886-95. [PMID: 23153485 DOI: 10.1016/j.devcel.2012.10.009] [Citation(s) in RCA: 358] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Whereas some rare lipids contribute to the identity of cell organelles, we focus on the abundant lipids that form the matrix of organelle membranes. Observations using bioprobes and peripheral proteins, notably sensors of membrane curvature, support the prediction that the cell contains two broad membrane territories: the territory of loose lipid packing, where cytosolic proteins take advantage of membrane defects, and the territory of electrostatics, where proteins are attracted by negatively charged lipids. The contrasting features of these territories provide specificity for reactions occurring along the secretory pathway, on the plasma membrane, and also on lipid droplets and autophagosomes.
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Affiliation(s)
- Joëlle Bigay
- Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia Antipolis et CNRS, 06560 Valbonne, France
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89
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Hsieh WT, Hsu CJ, Capraro BR, Wu T, Chen CM, Yang S, Baumgart T. Curvature sorting of peripheral proteins on solid-supported wavy membranes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:12838-43. [PMID: 22881196 PMCID: PMC3721505 DOI: 10.1021/la302205b] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Cellular membrane deformation and the associated redistribution of membrane-bound proteins are important aspects of membrane function. Current model membrane approaches for studying curvature sensing are limited to positive curvatures and often require complex and delicate experimental setups. To overcome these challenges, we fabricated a wavy substrate by imposing a range of curvatures onto an adhering lipid bilayer membrane. We examined the curvature sorting of several peripheral proteins binding to the wavy membrane and observed them to partition into distinct regions of curvature. Furthermore, single-molecule imaging experiments suggested that the curvature sensing of proteins on low-curvature substrates requires cooperative interactions.
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Affiliation(s)
- Wan-Ting Hsieh
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA19104
| | - Chih-Jung Hsu
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA19104
| | | | - Tingting Wu
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA19104
| | - Chi-Mon Chen
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA19104
| | - Shu Yang
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA19104
| | - Tobias Baumgart
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA19104
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90
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Singh P, Mahata P, Baumgart T, Das SL. Curvature sorting of proteins on a cylindrical lipid membrane tether connected to a reservoir. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:051906. [PMID: 23004787 PMCID: PMC3679408 DOI: 10.1103/physreve.85.051906] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2012] [Revised: 04/16/2012] [Indexed: 05/08/2023]
Abstract
Membrane curvature of a biological cell is actively involved in various fundamental cell biological functions. It has been discovered that membrane curvature and binding of peripheral membrane proteins follow a symbiotic relationship. The exact mechanism behind this interplay of protein binding and membrane curvature has not yet been properly understood. To improve understanding of the mechanism, we study curvature sorting of proteins in a model system consisting of a tether pulled from a giant unilamellar vesicle using mechanical-thermodynamic models. The concentration of proteins bound to the membrane changes significantly due to curvature. This has also been observed in experiments by other researchers. We also find that there is a phase transition based on protein concentration and we discuss the coexistence of phases and stability of solutions. Furthermore, when sorting is favorable, the increase in protein concentration stabilizes the tether in the sense that less pulling force is required to maintain the tether. A similar mechanism may be in place, when motor proteins pull tethers from donor membranes.
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Affiliation(s)
- Pankaj Singh
- Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208016, India
| | - Paritosh Mahata
- Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208016, India
| | - Tobias Baumgart
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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