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 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 Stabilization of Supramolecular Membrane Protein-Lipid Bilayer Assemblies Through Immobilization in a Crystalline Exoskeleton

2021 ◽  
Author(s):  
Fabian C. Herbert ◽  
Sameera Abeyrathna ◽  
Nisansala Abeyrathna ◽  
Yalini Wijesundara ◽  
Olivia Brohlin ◽  
...  
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Elevated Temperatures ◽  
Transmembrane Proteins ◽  
Structural Instability ◽  
Supramolecular Complexes ◽  
Protein Assemblies ◽  
Metal Transporters ◽  
Structure And Activity ◽  
Detergent Micelles

<div> <div> <div><div><div><p>Artificial native-like lipid bilayer systems constructed from phospholipids assembling into unilamellar liposomes allow the reconstitution of detergent-solubilized transmembrane proteins into supramolecular lipid-protein assemblies called proteoliposomes, which mimic cellular membranes. Stabilization of these complexes remains challenging because of their chemical composition, the hydrophobicity and structural instability of membrane proteins, and the lability of interactions between protein, detergent, and lipids within micelles and lipid bilayers. In this work we demonstrate that metastable lipid, protein-detergent, and protein-lipid supramolecular complexes can be successfully generated and immobilized within zeolitic-imidazole framework (ZIF) to enhance their stability against chemical and physical stressors. Upon immobilization in ZIF bio-composites, blank liposomes, and model transmembrane metal transporters in detergent micelles or embedded in proteoliposomes resist elevated temperatures, exposure to chemical denaturants, aging, and mechanical stresses. Extensive morphological and functional charac- terization of the assemblies upon exfoliation reveal that all these complexes encapsulated within the framework maintain their native morphology, structure, and activity, which is otherwise lost rapidly without immobilization.</p></div></div></div> </div> </div>

scholarly journals Cryo-EM structure of an activated GPCR-G protein complex in lipid nanodiscs

2020 ◽  
Author(s):  
Gerhard Wagner ◽  
Meng Zhang ◽  
Miao Gui ◽  
Zi-Fu Wang ◽  
Christoph Gorgulla ◽  
...  
Keyword(s):  
Complex Formation ◽  
G Protein ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Protein Interactions ◽  
Protein Complex ◽  
Lipid Membrane ◽  
Protein Complexes ◽  
Structural Basis ◽  
Downstream Signaling

Abstract G protein coupled receptors (GPCRs) are the largest superfamily of transmembrane proteins and the targets of over 30% of currently marketed pharmaceuticals. Although several structures have been solved for GPCR-G protein complexes, structural studies of the complex in a physiological lipid membrane environment are lacking. Here, we report cryo-EM structures of lipid bilayer-bound complexes of neurotensin, neurotensin receptor 1, and Gai1b1g1 protein in two conformational states, resolved to 4.1 and 4.2 Å resolution. The structures were determined in lipid bilayer without any stabilizing antibodies/nanobodies, and thus provide a native-like platform for understanding the structural basis of GPCR-G protein complex formation. Our structures reveal an extended network of protein-protein interactions at the GPCR-G protein interface compared to in detergent micelles, defining roles for the lipid membrane in modulating the structure and dynamics of complex formation, and providing a molecular explanation for the stronger interaction between GPCR and G protein in lipid bilayers. We propose a detailed allosteric mechanism for GDP release, providing new insights into the activation of G proteins for downstream signaling.

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.

scholarly journals Stabilization of Supramolecular Membrane Protein-Lipid Bilayer Assemblies Through Immobilization in a Crystalline Exoskeleton

2021 ◽  
Author(s):  
Fabian C. Herbert ◽  
Sameera Abeyrathna ◽  
Nisansala Abeyrathna ◽  
Yalini Wijesundara ◽  
Olivia Brohlin ◽  
...  
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Elevated Temperatures ◽  
Transmembrane Proteins ◽  
Structural Instability ◽  
Supramolecular Complexes ◽  
Protein Assemblies ◽  
Metal Transporters ◽  
Structure And Activity ◽  
Detergent Micelles

<div> <div> <div><div><div><p>Artificial native-like lipid bilayer systems constructed from phospholipids assembling into unilamellar liposomes allow the reconstitution of detergent-solubilized transmembrane proteins into supramolecular lipid-protein assemblies called proteoliposomes, which mimic cellular membranes. Stabilization of these complexes remains challenging because of their chemical composition, the hydrophobicity and structural instability of membrane proteins, and the lability of interactions between protein, detergent, and lipids within micelles and lipid bilayers. In this work we demonstrate that metastable lipid, protein-detergent, and protein-lipid supramolecular complexes can be successfully generated and immobilized within zeolitic-imidazole framework (ZIF) to enhance their stability against chemical and physical stressors. Upon immobilization in ZIF bio-composites, blank liposomes, and model transmembrane metal transporters in detergent micelles or embedded in proteoliposomes resist elevated temperatures, exposure to chemical denaturants, aging, and mechanical stresses. Extensive morphological and functional charac- terization of the assemblies upon exfoliation reveal that all these complexes encapsulated within the framework maintain their native morphology, structure, and activity, which is otherwise lost rapidly without immobilization.</p></div></div></div> </div> </div>

scholarly journals DNA-Encircled Lipid Bilayers

2018 ◽  
Author(s):  
Katarina Iric ◽  
Madhumalar Subramanian ◽  
Jana Oertel ◽  
Nayan P. Agarwal ◽  
Michael Matthies ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Protein Interactions ◽  
Protein Function ◽  
Dna Nanotechnology ◽  
Lipid Vesicles ◽  
Associated Proteins

ABSTRACTLipid bilayers and lipid-associated proteins play a crucial role in biology. As in vivo studies and manipulation are inherently difficult, several membrane-mimetic systems have been developed to enable investigation of lipidic phases, lipid-protein interactions, membrane protein function and membrane structure in vitro. Controlling the size and shape, or site-specific functionalization is, however, difficult to achieve with established membrane mimetics based on membrane scaffolding proteins, polymers or peptides. In this work, we describe a route to leverage the unique programmability of DNA nanotechnology and create DNA-encircled bilayers (DEBs), which are made of multiple copies of an alkylated oligonucleotide hybridized to a single-stranded minicircle. To stabilize the hydrophobic rim of the lipid bilayer, and to prevent formation of lipid vesicles, we introduced up to 2 alkyl chains per helical that point to the inside of the toroidal DNA ring and interact with the hydrophobic side chains of the encapsulated lipid bilayer. The DEB approach described herein provides unprecedented control of size, and allows the orthogonal functionalizations and arrangement of engineered membrane nanoparticles and will become a valuable tool for biophysical investigation of lipid phases and lipid-associated proteins and complexes including structure determination of membrane proteins and pharmacological screenings of membrane proteins.

scholarly journals Stabilization of Supramolecular Membrane Protein-Lipid Bilayer Assemblies Through Immobilization in a Crystalline Exoskeleton

2020 ◽  
Author(s):  
Fabian C. Herbert ◽  
Sameera Abeyrathna ◽  
Nisansala Abeyrathna ◽  
Yalini Wijesundara ◽  
Olivia Brohlin ◽  
...  
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Elevated Temperatures ◽  
Functional Characterization ◽  
Transmembrane Proteins ◽  
Protein Assemblies ◽  
Metal Transporters ◽  
Structure And Activity ◽  
Detergent Micelles

<div> <div> <div> <p>Artificial native-like lipid bilayer systems constructed from phospholipids assembling into unilamel- lar liposomes allow the reconstitution of detergent-solubilized transmembrane proteins into supramolecular lipid-protein assemblies called proteoliposomes, which mimic cellular membranes. Stabilization of these com- plexes remains challenging because of their chemical composition, the hydrophobicity and structural instabil- ity of membrane proteins, and the lability of interactions between protein, detergent, and lipids within micelles and lipid bilayers. In this work we demonstrate that metastable lipid, protein-detergent, and protein-lipid su- pramolecular complexes can be successfully generated and immobilized within zeolitic-imidazole framework- 8 (ZIF-8) to enhance their stability against chemical and physical stressors. Upon immobilization in ZIF-8 bio- composites, blank liposomes, and model transmembrane metal transporters in detergent micelles or embed- ded in proteoliposomes resist elevated temperatures, exposure to chemical denaturants, aging, and mechanical stresses. Extensive morphological and functional characterization of the assemblies upon exfoliation reveal that all these complexes encapsulated within the framework maintain their native morphology, structure, and activity, which is otherwise lost rapidly without immobilization. </p> </div> </div> </div>

scholarly journals A proteoliposome-based system reveals how lipids control photosynthetic light harvesting

2020 ◽  
Vol 295 (7) ◽  
pp. 1857-1866 ◽  
Author(s):  
Stefanie Tietz ◽  
Michelle Leuenberger ◽  
Ricarda Höhner ◽  
Alice H. Olson ◽  
Graham R. Fleming ◽  
...  
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Protein Interactions ◽  
Light Harvesting ◽  
Single Photon ◽  
Pressure Profile ◽  
Cd Spectroscopy ◽  
Quantum Yields ◽  
The Impact

Integral membrane proteins are exposed to a complex and dynamic lipid environment modulated by nonbilayer lipids that can influence protein functions by lipid-protein interactions. The nonbilayer lipid monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in plant photosynthetic thylakoid membranes, but its impact on the functionality of energy-converting membrane protein complexes is unknown. Here, we optimized a detergent-based reconstitution protocol to develop a proteoliposome technique that incorporates the major light-harvesting complex II (LHCII) into compositionally well-defined large unilamellar lipid bilayer vesicles to study the impact of MGDG on light harvesting by LHCII. Using steady-state fluorescence spectroscopy, CD spectroscopy, and time-correlated single-photon counting, we found that both chlorophyll fluorescence quantum yields and fluorescence lifetimes clearly indicate that the presence of MGDG in lipid bilayers switches LHCII from a light-harvesting to a more energy-quenching mode that dissipates harvested light into heat. It is hypothesized that in the in vitro system developed here, MGDG controls light harvesting of LHCII by modulating the hydrostatic lateral membrane pressure profile in the lipid bilayer sensed by LHCII-bound peripheral pigments.

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.

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