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Membrane curvature

Agnieszka Martyna, Basma Bahsoun, Matthew D Badham, Saipraveen Srinivasan, Mark J Howard, Jeremy S Rossman
Membrane scission is a crucial step in all budding processes, from endocytosis to viral budding. Many proteins have been associated with scission, though the underlying molecular details of how scission is accomplished often remain unknown. Here, we investigate the process of M2-mediated membrane scission during the budding of influenza viruses. Residues 50-61 of the viral M2 protein bind membrane and form an amphipathic α-helix (AH). Membrane binding requires hydrophobic interactions with the lipid tails but not charged interactions with the lipid headgroups...
March 20, 2017: Scientific Reports
Benny Wah, Jeffrey Michael Breidigan, Joseph Adams, Piotr Horbal, Sumit Garg, Lionel Porcar, Ursula Perez-Salas
Maintaining compositional lipid gradients across membranes in animal cells is essential to biological function, but what is the energetic cost to maintain these differences? It has long been recognized that studying the passive movement of lipids in membranes can provide insight into this toll. Unfortunately the reported values of inter, and particularly, intra- lipid transport rates of lipids in membranes show significant differences. To overcome this difficulty, biases introduced by experimental approaches have to be identified...
March 16, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Christina L Ting, Marcus Müller
Using self-consistent field theory (SCFT), we develop an accurate, local expression for the stress profiles in membranes and soft matter interfaces, in general. The bond stresses are expressed in terms of pre-computed chain propagators, which are used to describe the statistical weight of the molecules and therefore require minimal additional calculations. In addition, we overcome the resolution limit of the molecular bond length by including the Irving and Kirkwood bond assignment and recover a constant normal stress profile across an interface...
March 14, 2017: Journal of Chemical Physics
Bartosz Różycki, Reinhard Lipowsky
No abstract text is available yet for this article.
March 14, 2017: Journal of Chemical Physics
Philip P Cheney, Alan W Weisgerber, Alec M Feuerbach, Michelle K Knowles
The plasma membrane is a highly compartmentalized, dynamic material and this organization is essential for a wide variety of cellular processes. Nanoscale domains allow proteins to organize for cell signaling, endo- and exocytosis, and other essential processes. Even in the absence of proteins, lipids have the ability to organize into domains as a result of a variety of chemical and physical interactions. One feature of membranes that affects lipid domain formation is membrane curvature. To directly test the role of curvature in lipid sorting, we measured the accumulation of two similar lipids, 1,2-Dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DHPE) and hexadecanoic acid (HDA), using a supported lipid bilayer that was assembled over a nanopatterned surface to obtain regions of membrane curvature...
March 15, 2017: Membranes
Xinbo Wang, Shanshan Li, Haicheng Wang, Wenqing Shui, Junjie Hu
The tubular network is a critical part of the endoplasmic reticulum (ER). The network is shaped by the reticulons and REEPs/Yop1p that generate tubules by inducing high membrane curvature, and the dynamin-like GTPases atlastin and Sey1p/RHD3 that connect tubules via membrane fusion. However, the specific functions of this ER domain are not clear. Here, we isolated tubule-based microsomes from Saccharomyces cerevisiae via classical cell fractionation and detergent-free immunoprecipitation of Flag-tagged Yop1p, which specifically localizes to ER tubules...
March 13, 2017: ELife
Sandra-Fausia Soukup, Patrik Verstreken
Synapses are very specialized compartments with high metabolic demand to maintain neurotransmission, an essential step for basic brain function. Neurons are post-mitotic and synapses need to stay functional over time-sometimes over decades. Given that synapses are often at a long distance from the cell body, they must use local mechanisms to regulate protein quality control. We show that macroautophagy/autophagy is one of these local processes and found that it is under strict control of the synapse-enriched protein EndoA/Endophilin-A, previously only implicated in endocytosis...
February 15, 2017: Autophagy
Leonie van 't Hag, Sally L Gras, Charlotte E Conn, Calum J Drummond
Ordered amphiphile self-assembly materials with a tunable three-dimensional (3D) nanostructure are of fundamental interest, and crucial for progressing several biological and biomedical applications, including in meso membrane protein crystallization, as drug and medical contrast agent delivery vehicles, and as biosensors and biofuel cells. In binary systems consisting of an amphiphile and a solvent, the ability to tune the 3D cubic phase nanostructure, lipid bilayer properties and the lipid mesophase is limited...
March 10, 2017: Chemical Society Reviews
Norbert Kučerka, Ermuhammad Dushanov, Kholmirzo T Kholmurodov, John Katsaras, Daniela Uhríková
Interactions of calcium (Ca(2+)) and zinc (Zn(2+)) cations with biomimetic membranes made of dipalmitoylphosphatidylcholine (DPPC) were studied by small angle neutron diffraction (SAND). Experiments show that the structure of these lipid bilayers is differentially affected by the two divalent cations. Initially, both Ca(2+) and Zn(2+) cause DPPC bilayers to thicken, while further increases in Ca(2+) concentration result in the bilayer thinning, eventually reverting to having the same thickness as pure DPPC...
March 17, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Changjin Huang, David Quinn, Yoel Sadovsky, Subra Suresh, K Jimmy Hsia
When detergents and phospholipid membranes are dispersed in aqueous solutions, they tend to self-assemble into vesicles of various shapes and sizes by virtue of their hydrophobic and hydrophilic segments. A clearer understanding of such vesiculation processes holds promise for better elucidation of human physiology and disease, and paves the way to improved diagnostics, drug development, and drug delivery. Here we present a detailed analysis of the energetics and thermodynamics of vesiculation by recourse to nonlinear elasticity, taking into account large deformation that may arise during the vesiculation process...
March 14, 2017: Proceedings of the National Academy of Sciences of the United States of America
Lushen Li, Shaneen S Baxter, Ning Gu, Min Ji, Xi Zhan
Surface expression of chemokine receptor CXCR4 is downregulated by MIM, a member of the inverse BAR (I-BAR) domain protein family that recognizes and generates membranes with negative curvatures. Yet, the mechanism for the regulation is unknown. Here, we showed that MIM formed a complex with CXCR4 via binding to E3 ubiquitin ligase AIP4 in response to SDF-1. Overexpression of MIM promoted CXCR4 ubiquitination, inhibited cellular response to SDF-1, caused accumulation and aggregation of MVBs in the cytoplasm, and promoted CXCR4 sorting into MVBs in a manner depending on binding to AIP4...
March 6, 2017: Journal of Cell Science
Janin Lautenschläger, Clemens F Kaminski, Gabriele S Kaminski Schierle
α-Synuclein is known as a presynaptic protein that binds to small synaptic vesicles. Recent studies suggest that α-synuclein is not only attracted to these tiny and therewith highly curved membranes, but that in fact the sensing and regulation of membrane curvature is part of its physiological function. Moreover, recent studies have suggested that α-synuclein plays a role in the endocytosis of synaptic vesicles, and have provided support for a function of α-synuclein during exo- and endocytosis in which curvature sensing and membrane stabilization are crucial steps...
March 1, 2017: Trends in Cell Biology
Daryna Tarasenko, Mariam Barbot, Daniel C Jans, Benjamin Kroppen, Boguslawa Sadowski, Gudrun Heim, Wiebke Möbius, Stefan Jakobs, Michael Meinecke
The inner membrane (IM) of mitochondria displays an intricate, highly folded architecture and can be divided into two domains: the inner boundary membrane adjacent to the outer membrane and invaginations toward the matrix, called cristae. Both domains are connected by narrow, tubular membrane segments called cristae junctions (CJs). The formation and maintenance of CJs is of vital importance for the organization of the mitochondrial IM and for mitochondrial and cellular physiology. The multisubunit mitochondrial contact site and cristae organizing system (MICOS) was found to be a major factor in CJ formation...
March 2, 2017: Journal of Cell Biology
Sabina Merlo, Paolo Poma, Eleonora Crisà, Dino Faralli, Marco Soldo
In this work, we have applied optical low-coherence reflectometry (OLCR), implemented with infra-red light propagating in fiberoptic paths, to perform static and dynamic analyses on piezo-actuated glass micro-membranes. The actuator was fabricated by means of thin-film piezoelectric MEMS technology and was employed for modifying the micro-membrane curvature, in view of its application in micro-optic devices, such as variable focus micro-lenses. We are here showing that OLCR incorporating a near-infrared superluminescent light emitting diode as the read-out source is suitable for measuring various parameters such as the micro-membrane optical path-length, the membrane displacement as a function of the applied voltage (yielding the piezo-actuator hysteresis) as well as the resonance curve of the fundamental vibration mode...
February 25, 2017: Sensors
Ulrich Salzer, Julius Kostan, Kristina Djinović-Carugo
The BAR domain is the eponymous domain of the "BAR-domain protein superfamily", a large and diverse set of mostly multi-domain proteins that play eminent roles at the membrane cytoskeleton interface. BAR domain homodimers are the functional units that peripherally associate with lipid membranes and are involved in membrane sculpting activities. Differences in their intrinsic curvatures and lipid-binding properties account for a large variety in membrane modulating properties. Membrane activities of BAR domains are further modified and regulated by intramolecular or inter-subunit domains, by intermolecular protein interactions, and by posttranslational modifications...
February 27, 2017: Cellular and Molecular Life Sciences: CMLS
Arthur A Evans, Basanta Bhaduri, Gabriel Popescu, Alex J Levine
The thermal fluctuations of membranes and nanoscale shells affect their mechanical characteristics. Whereas these fluctuations are well understood for flat membranes, curved shells show anomalous behavior due to the geometric coupling between in-plane elasticity and out-of-plane bending. Using conventional shallow shell theory in combination with equilibrium statistical physics we theoretically demonstrate that thermalized shells containing regions of negative Gaussian curvature naturally develop anomalously large fluctuations...
February 27, 2017: Proceedings of the National Academy of Sciences of the United States of America
Stefan Piehler, Tom Dietrich, Philipp Wittmüss, Oliver Sawodny, Marwan Abdou Ahmed, Thomas Graf
We present deformable mirrors for the intra-cavity use in high-power thin-disk laser resonators. The refractive power of these mirrors is continuously adaptable from -0.7 m<sup>-1</sup> to 0.3 m<sup>-1</sup>, corresponding to radii of curvature ranging between 2.86 m (convex) and 6.67 m (concave). The optimized shape of the mirror membrane enables a very low peak-to-valley deviation from a paraboloid deformation over a large area. With the optical performance of our mirrors being equal to that of standard HR mirrors, we were able to demonstrate the tuning of the beam quality of a thin-disk laser in a range of M<sup>2</sup> = 3 to M<sup>2</sup> = 1 during laser operation at output powers as high as 1...
February 20, 2017: Optics Express
Achim Guckenberger, Stephan Gekle
Cell membranes are vital to shield a cell's interior from the environment. At the same time they determine to a large extent the cell's mechanical resistance to external forces. In recent years there has been considerable interest in the accurate computational modeling of such membranes, driven mainly by the amazing variety of shapes that red blood cells and model systems such as vesicles can assume in external flows. Given that the typical height of a membrane is only a few nanometers while the surface of the cell extends over many micrometers, physical modeling approaches mostly consider the interface as a two-dimensional elastic continuum...
February 27, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Anthony R Braun, Michael M Lacy, Vanessa C Ducas, Elizabeth Rhoades, Jonathan N Sachs
α-Synuclein is the primary protein found in Lewy bodies, the protein and lipid aggregates associated with Parkinson's disease and Lewy body dementia. The protein folds into a uniquely long amphipathic α-helix (AH) when bound to a membrane, and at high enough concentrations, it induces large-scale remodeling of membranes (tubulation and vesiculation). By engineering a less hydrophobic variant of α-Synuclein, we previously showed that the energy associated with binding of α-Synuclein's AH correlates with the extent of membrane remodeling (Braun et al...
February 26, 2017: Journal of Membrane Biology
Jaime Agudo-Canalejo, Reinhard Lipowsky
Biological membranes and lipid vesicles often display complex shapes with non-uniform membrane curvature. When adhesive nanoparticles with chemically uniform surfaces come into contact with such membranes, they exhibit four different engulfment regimes as recently shown by a systematic stability analysis. Depending on the local curvature of the membrane, the particles either remain free, become partially or completely engulfed by the membrane, or display bistability between free and completely engulfed states...
February 23, 2017: Soft Matter
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