scholarly journals Membrane Constriction by ESCRT-III Proteins Induces Structural Lipid Bilayer Asymmetries

2021 ◽  
Author(s):  
Frank Russell Moss ◽  
James Lincoff ◽  
Maxwell Tucker ◽  
Arshad Mohammed ◽  
Michael Grabe ◽  
...  
Keyword(s):  
Lipid Bilayers ◽  
Protein Interactions ◽  
Electrostatic Interactions ◽  
Membrane Surface ◽  
Spontaneous Curvature ◽  
Membrane Mechanics ◽  
Vesicular Traffic ◽  
Outer Leaflet ◽  
Lipid Diffusion ◽  
Lipid Protein Interactions

Cells utilize molecular machines to form and remodel their membrane-defined compartments' compositions, shapes, and connections. The regulated activity of these membrane remodeling machines drives processes like vesicular traffic and organelle homeostasis. Although molecular patterning within membranes is essential to cellular life, characterizing the composition and structure of realistic biological membranes on the molecular length scale remains a challenge, particularly during membrane shape transformations. Here, we employed an ESCRT-III protein coating model system to investigate how membrane-binding proteins bind to and alter the structural patterns within lipid bilayers. We observe leaflet-level and localized lipid structures within a constricted and thinned membrane nanotube. To map the fine structure of these membranes, we compared simulated bilayer nanotubes with experimental cryo-EM reconstructions of native membranes and membranes containing halogenated lipid analogs. Halogenated lipids scatter electrons more strongly, and analysis of their surplus scattering enabled us to estimate the concentrations of lipids within each leaflet and to estimate lipid shape and sorting changes induced by high curvature and lipid-protein interactions. Specifically, we found that cholesterol enriched within the inner leaflet due to its spontaneous curvature, while acidic lipids enriched in the outer leaflet due to electrostatic interactions with the protein coat. The docosahexaenoyl (DHA) polyunsaturated chain-containing lipid SDPC enriched strongly at membrane-protein contact sites. Simulations and imaging of brominated SDPC showed how a pair of phenylalanine residues opens a hydrophobic defect in the outer leaflet and how DHA tails stabilize the defect and "snorkel" up to the membrane surface to interact with these side chains. This highly curved nanotube differs markedly from protein-free, flat bilayers in leaflet thickness, lipid diffusion, and other structural asymmetries with implications for our understanding of membrane mechanics.

scholarly journals Structure and activity of lipid bilayer within a membrane-protein transporter

2018 ◽  
Vol 115 (51) ◽  
pp. 12985-12990 ◽  
Author(s):  
Weihua Qiu ◽  
Ziao Fu ◽  
Guoyan G. Xu ◽  
Robert A. Grassucci ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Protein Interactions ◽  
Extraction Methods ◽  
Free System ◽  
Outer Leaflet ◽  
Proton Relay ◽  
Native Cell ◽  
Lipid Protein Interactions ◽  
Structure And Activity

Membrane proteins function in native cell membranes, but extraction into isolated particles is needed for many biochemical and structural analyses. Commonly used detergent-extraction methods destroy naturally associated lipid bilayers. Here, we devised a detergent-free method for preparing cell-membrane nanoparticles to study the multidrug exporter AcrB, by cryo-EM at 3.2-Å resolution. We discovered a remarkably well-organized lipid-bilayer structure associated with transmembrane domains of the AcrB trimer. This bilayer patch comprises 24 lipid molecules; inner leaflet chains are packed in a hexagonal array, whereas the outer leaflet has highly irregular but ordered packing. Protein side chains interact with both leaflets and participate in the hexagonal pattern. We suggest that the lipid bilayer supports and harmonizes peristaltic motions through AcrB trimers. In AcrB D407A, a putative proton-relay mutant, lipid bilayer buttresses protein interactions lost in crystal structures after detergent-solubilization. Our detergent-free system preserves lipid–protein interactions for visualization and should be broadly applicable.

scholarly journals Local sensitivity analysis of the ‘Membrane shape equation’ derived from the Helfrich energy

2020 ◽  
Author(s):  
P. Rangamani ◽  
A. Behzadan ◽  
M. Holst
Keyword(s):  
Differential Equations ◽  
Lipid Bilayers ◽  
Numerical Study ◽  
Membrane Vesicles ◽  
Energy Functional ◽  
Specific Model ◽  
Model Systems ◽  
Spontaneous Curvature ◽  
Membrane Mechanics ◽  
Curvature Term

AbstractThe Helfrich energy is commonly used to model the elastic bending energy of lipid bilayers in membrane mechanics. The governing differential equations for certain geometric characteristics of the shape of the membrane can be obtained by applying variational methods (minimization principles) to the Helfrich energy functional and are well-studied in the axisymmetric framework. However, the Helfrich energy functional and the resulting differential equations involve a number of parameters, and there is little explanation of the choice of parameters in the literature, particularly with respect to the choice of the “spontaneous curvature” term that appears in the functional. In this paper, we present a careful analytical and numerical study of certain aspects of parametric sensitivity of Helfrich’s model. Using simulations of specific model systems, we demonstrate the application of our scheme to the formation of spherical buds and pearled shapes in membrane vesicles.

scholarly journals Local sensitivity analysis of the “membrane shape equation” derived from the Helfrich energy

2020 ◽  
pp. 108128652095388
Author(s):  
P Rangamani ◽  
A Behzadan ◽  
M Holst
Keyword(s):  
Differential Equations ◽  
Lipid Bilayers ◽  
Numerical Study ◽  
Membrane Vesicles ◽  
Energy Functional ◽  
Specific Model ◽  
Model Systems ◽  
Spontaneous Curvature ◽  
Membrane Mechanics ◽  
Curvature Term

The Helfrich energy is commonly used to model the elastic bending energy of lipid bilayers in membrane mechanics. The governing differential equations for certain geometric characteristics of the shape of the membrane can be obtained by applying variational methods (minimization principles) to the Helfrich energy functional and are well studied in the axisymmetric framework. However, the Helfrich energy functional and the resulting differential equations involve a number of parameters, and there is little explanation of the choice of parameters in the literature, particularly with respect to the choice of the “spontaneous curvature” term that appears in the functional. In this paper, we present a careful analytical and numerical study of certain aspects of parametric sensitivity of Helfrich’s model. Using simulations of specific model systems, we demonstrate the application of our scheme to the formation of spherical buds and pearled shapes in membrane vesicles.

scholarly journals LUMENAL PLASMA MEMBRANE OF THE URINARY BLADDER

1972 ◽  
Vol 53 (1) ◽  
pp. 73-91 ◽  
Author(s):  
L. Andrew Staehelin ◽  
Francis J. Chlapowski ◽  
Mary A. Bonneville
Keyword(s):  
Urinary Bladder ◽  
Lipid Bilayers ◽  
Membrane Surface ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Transitional Epithelium ◽  
Permeability Barrier ◽  
Outer Leaflet ◽  
Cytoplasmic Filaments ◽  
Membrane Components

To determine the three-dimensional structure of the lumenal membrane of transitional epithelium, a study was made of sectioned, negatively stained, and freeze-etched specimens from intact epithelium and membrane fractions from rabbit urinary bladder. Particulate membrane components are confined to plaque regions within which the unit membrane is asymmetric, having a thicker outer leaflet. Transversely fractured freeze-etched plaques display a thick (∼80 A), particulate lumenal leaflet and a thin (∼40 A) cytoplasmic one. Four different faces of the two leaflets can be distinguished: two complementary, split, inner membrane faces exposed by freeze-cleaving the bilayer and two external (lumenal and cytoplasmic) membrane surfaces revealed by deep-etching. On the split, inner face of the lumenal leaflet appear polygonal plaques of hexagonally arranged particles. These fit into holes observed on the complementary, split, innerface of the cytoplasmic leaflet. The particles, which have a center-to-center spacing of ∼160 A, also seem to protrude from the external surface of the lumenal leaflet, where their subunits (∼50 A in diameter) are revealed by freeze-etching and negative staining. The plaques are separated from each other by smooth-surfaced regions, which cleave like simple lipid bilayers. Since the array of plaque particles covers only ∼73% of the membrane surface area, whereas 27% is taken up by particle-free interplaque regions, the presence of particles cannot in itself entirely account for the permeability barrier of the lumenal membrane. Although no particles are observed protruding from the cytoplasmic surface of the membrane, cytoplasmic filaments are attached to it by short, cross-bridge-like filaments that seem to contact the particles within the membrane. These long cytoplasmic filaments cross-link adjacent plaques. Therefore, we suggest that at least one function of the particles is to serve as anchoring sites for cytoplasmic filaments, which limit the expansion of the lumenal membrane during distention of the bladder, thereby preventing it from rupturing. The particle-free interplaque regions probably function as hinge areas between the stiff plaques, allowing the membrane to fold up when the bladder is contracted.

scholarly journals Lateral electric field inhibits gel-to-fluid transition in lipid bilayers

2021 ◽  
Author(s):  
Nidhin Thomas ◽  
Ashutosh Agrawal
Keyword(s):  
Electric Field ◽  
Melting Temperature ◽  
Lipid Bilayers ◽  
Electric Fields ◽  
Protein Interactions ◽  
Atomic Scale ◽  
Lateral Electric Field ◽  
Lipid Protein Interactions ◽  
Dynamics Simulations ◽  
Induced Changes

We report evidence of lateral electric field-induced changes in the phase transition temperatures of lipid bilayers. Our atomic scale molecular dynamics simulations show that lateral electric field increases the melting temperature of DPPC, POPC and POPE bilayers. Remarkably, this shift in melting temperature is only induced by lateral electric field, and not normal electric field. This mechanism could provide new mechanistic insights into lipid-lipid and lipid-protein interactions in the presence of endogenous and exogenous electric fields.

Membrane Protein–Lipid Interactions Probed Using Mass Spectrometry

2019 ◽  
Vol 88 (1) ◽  
pp. 85-111 ◽  
Author(s):  
Jani Reddy Bolla ◽  
Mark T. Agasid ◽  
Shahid Mehmood ◽  
Carol V. Robinson
Keyword(s):  
Mass Spectrometry ◽  
Membrane Protein ◽  
Lipid Bilayers ◽  
Protein Interactions ◽  
Native Mass Spectrometry ◽  
Lipid Interactions ◽  
X Ray Crystallography ◽  
Native Ms ◽  
Molecular Aspects ◽  
Lipid Protein Interactions

Membrane proteins that exist in lipid bilayers are not isolated molecular entities. The lipid molecules that surround them play crucial roles in maintaining their full structural and functional integrity. Research directed at investigating these critical lipid–protein interactions is developing rapidly. Advancements in both instrumentation and software, as well as in key biophysical and biochemical techniques, are accelerating the field. In this review, we provide a brief outline of structural techniques used to probe protein–lipid interactions and focus on the molecular aspects of these interactions obtained from native mass spectrometry (native MS). We highlight examples in which lipids have been shown to modulate membrane protein structure and show how native MS has emerged as a complementary technique to X-ray crystallography and cryo–electron microscopy. We conclude with a short perspective on future developments that aim to better understand protein–lipid interactions in the native environment.

scholarly journals The influence of phosphatidylserine localisation and lipid phase on membrane remodelling by the ESCRT-II/ESCRT-III complex

2020 ◽  
Author(s):  
Andrew Booth ◽  
Christopher J. Marklew ◽  
Barbara Ciani ◽  
Paul A. Beales
Keyword(s):  
Lipid Bilayers ◽  
Electrostatic Interactions ◽  
Annexin V ◽  
Membrane Curvature ◽  
Lipid Phase ◽  
Membrane Mechanics ◽  
Anionic Phospholipids ◽  
Escrt Complex ◽  
Phospholipid Distribution ◽  
Curvature Driven

AbstractThe endosomal sorting complex required for transport (ESCRT) organises in supramolecular structures on the surface of lipid bilayers to drive membrane invagination and scission of intraluminal vesicles (ILVs), a process also controlled by membrane mechanics. However, ESCRT association with the membrane is also mediated by electrostatic interactions with anionic phospholipids. Phospholipid distribution within natural biomembranes is inhomogeneous due to, for example, the formation of lipid rafts and curvature-driven lipid sorting. Here, we have used phase-separated giant unilamellar vesicles (GUVs) to investigate the link between phosphatidylserine (PS)-rich lipid domains and ESCRT activity. We employ GUVs composed of phase separating lipid mixtures, where unsaturated DOPS and saturated DPPS lipids are incorporated individually or simultaneously to enhance PS localisation in liquid disordered (Ld) and/or liquid ordered (Lo) domains, respectively. PS partitioning between the coexisting phases is confirmed by a fluorescent Annexin V probe. Ultimately, we find that ILV generation promoted by ESCRTs is significantly enhanced when PS lipids localise within Ld domains. However, the ILVs that form are rich in Lo lipids. We interpret this surprising observation as preferential recruitment of the Lo phase beneath the ESCRT complex due to its increased rigidity, where the Ld phase is favoured in the neck of the resultant buds to facilitate the high membrane curvature in these regions of the membrane during the ILV formation process. Ld domains offer lower resistance to membrane bending, demonstrating a mechanism by which the composition and mechanics of membranes can be coupled to regulate the location and efficiency of ESCRT activity.

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