The immune synapses reveal aberrant functions of CD8 T cells during chronic HIV infection

It is well-established that chronic HIV infection causes persistent low-grade inflammation that induces premature aging of the immune system in HIV patient including senescence of memory and effector CD8 T cells. To uncover the reasons of gradually diminished potency of CD8 T cells from chronically HIV infected people, we have analyzed cellular morphology and dynamics of the synaptic interface followed exposure of peripheral polyclonal CD8 T cells at various differentiation stages to planar lipid bilayers. The above parameters were linked to pattern of degranulation that determines efficiency of CD8 T cells cytolytic response. We found a large fraction of naive T cells from HIV infected people developing mature synapses and demonstrating focused degranulation, a signature of a differentiated T cells. Further differentiation of aberrant naive T cells leads to development of anomalous effector T cells undermining their capacity to control HIV and other viruses that could be contained otherwise.

Thermodynamic Modeling of Solvent-Assisted Lipid Bilayer Formation Process

The solvent-assisted lipid bilayer (SALB) formation method provides a simple and efficient, microfluidic-based strategy to fabricate supported lipid bilayers (SLBs) with rich compositional diversity on a wide range of solid supports. While various studies have been performed to characterize SLBs formed using the SALB method, relatively limited work has been carried out to understand the underlying mechanisms of SALB formation under various experimental conditions. Through thermodynamic modeling, we studied the experimental parameters that affect the SALB formation process, including substrate surface properties, initial lipid concentration, and temperature. It was found that all the parameters are critically important to successfully form high-quality SLBs. The model also helps to identify the range of parameter space within which conformal, homogeneous SLBs can be fabricated, and provides mechanistic guidance to optimize experimental conditions for lipid membrane-related applications.

Measuring anion binding at biomembrane interfaces

Understanding non-covalent molecular recognition events at biomembrane interfaces is important in biological, medicinal, and materials chemistry research.1 Despite the crucial regulatory roles of anion binding/transport processes at biomembranes, no information is available regarding how strongly anions can bind to naturally occurring or synthetic receptors in lipid bilayer environments compared to their well-established behaviour in solutions.2 To bridge this knowledge gap, we synthesised a flat macrocycle that possesses a record aqueous SO42– affinity among neutral receptors and exploited its unique fluorescence response at interfaces. We show that the determinants of anion binding are extraordinarily different in organic solvents and in lipid bilayers. The high charge density of dihydrogen phosphate and chloride ions prevails in DMSO, however in lipids they fail to bind the macrocycle. Perchlorate and iodide hardly bind in DMSO but show significant affinities for the macrocycle in lipids. Our results demonstrate a surprisingly great advantage of large, charge-diffuse anions to bind to a lipid-embedded synthetic receptor mainly attributed to their higher polarisabilities and deeper penetration into the bilayer, beyond the common knowledge of dehydration energy-governed selectivity. The elucidation of these principles enhances our understanding of biological anion recognition functions in membranes and guides the design of ionophores and molecular machines operating at biomembrane interfaces.

Nanoarchitectured air-stable supported lipid bilayer incorporating sucrose–bicelle complex system

Cell-membrane-mimicking supported lipid bilayers (SLBs) provide an ultrathin, self-assembled layer that forms on solid supports and can exhibit antifouling, signaling, and transport properties among various possible functions. While recent material innovations have increased the number of practically useful SLB fabrication methods, typical SLB platforms only work in aqueous environments and are prone to fluidity loss and lipid-bilayer collapse upon air exposure, which limits industrial applicability. To address this issue, herein, we developed sucrose–bicelle complex system to fabricate air-stable SLBs that were laterally mobile upon rehydration. SLBs were fabricated from bicelles in the presence of up to 40 wt% sucrose, which was verified by quartz crystal microbalance-dissipation (QCM-D) and fluorescence recovery after photobleaching (FRAP) experiments. The sucrose fraction in the system was an important factor; while 40 wt% sucrose induced lipid aggregation and defects on SLBs after the dehydration–rehydration process, 20 wt% sucrose yielded SLBs that exhibited fully recovered lateral mobility after these processes. Taken together, these findings demonstrate that sucrose–bicelle complex system can facilitate one-step fabrication of air-stable SLBs that can be useful for a wide range of biointerfacial science applications.

Unraveling membrane properties at the organelle-level with LipidDyn

Cellular membranes are formed from many different lipids in various amounts and proportions depending on the subcellular localization. The lipid composition of membranes is sensitive to changes in the cellular environment, and their alterations are linked to several diseases, including cancer. Lipids not only form lipid-lipid interactions but also interact with other biomolecules, including proteins, profoundly impacting each other. Molecular dynamics (MD) simulations are a powerful tool to study the properties of cellular membranes and membrane-protein interactions on different timescales and at varying levels of resolution. Over the last few years, software and hardware for biomolecular simulations have been optimized to routinely run long simulations of large and complex biological systems. On the other hand, high-throughput techniques based on lipidomics provide accurate estimates of the composition of cellular membranes at the level of subcellular compartments. The community needs computational tools for lipidomics and simulation data effectively interacting to better understand how changes in lipid compositions impact membrane function and structure. Lipidomic data can be analyzed to design biologically relevant models of membranes for MD simulations. Similar applications easily result in a massive amount of simulation data where the bottleneck becomes the analysis of the data to understand how membrane properties and membrane-protein interactions are changing in the different conditions. In this context, we developed LipidDyn, an in silico pipeline to streamline the analyses of MD simulations of membranes of different compositions. Once the simulations are collected, LipidDyn provides average properties and time series for several membrane properties such as area per lipid, thickness, diffusion motions, the density of lipid bilayers, and lipid enrichment/depletion. The calculations exploit parallelization and the pipelines include graphical outputs in a publication-ready form. We applied LipidDyn to different case studies to illustrate its potential, including membranes from cellular compartments and transmembrane protein domains. LipidDyn is implemented in Python and relies on open-source libraries. LipidDyn is available free of charge under the GNU General Public License from https://github.com/ELELAB/LipidDyn.

The amphoteric cartilage surface tested in the pH Range from 2.0 to 9.0

Background: Phospholipids adsorbed to negatively-charged proteoglycan matrix form phospholipid (membrane), have negatively charged surface (-PO4-) and are hydrophilic. Strong adsorption and strong cohesion are necessary for phospholipids to provide a good lubricant. The surface energy of spherical lipid bilayers have "bell-curve" shaped has amphoteric character and lowest surface energy at a pH 7.4 ± 1 of the natural joint. Objectives: The amphoteric character of the natural surface of the articular cartilage was determined by measuring the surface energy of the model spherical bilayer lipid membrane. It was found that the friction (f) vs. pH 2.0 to 9.0 of the pair (cartilage/cartilage) has the amphoteric character by exposing "bell-curve" shaped with an isoelectric point (IEP). Methods: The friction coefficient (f) was measured with the sliding pin-on-disc tribotester the friction between two surfaces (cartilage/cartilage) pair. The method of interfacial tension measurements of the spherical lipid bilayer model vs the pH over the range 0.2 to 9.0 was used. Results: The dependence of friction coefficient between two cartilage surfaces on the pH over the range 2.0 to 9.0 is demonstrated by a “bell - curve” in Fig. 2(A). The surface energy of a model spherical bilayer lipid membrane vs. the pH has the character of a “bell - curve” with an (IEP) is shown in Fig. 2(B). Conclusion: The amphoteric effect on friction between the bovine cartilage/cartilage contacts has been found to be highly sensitive to the pH of an aqueous solution. In this paper we demonstrate experimentally that the pH sensitivity of cartilage to friction provides a novel concept in joint lubrication on charged surfaces. The change in friction was consistently related to the change of charge density of an amphoteric surface.

Phosphatidylserine Exposed Lipid Bilayer Models for Understanding Cancer Cell Selectivity of Natural Compounds: A Molecular Dynamics Simulation Study

Development of drugs that are selectively toxic to cancer cells and safe to normal cells is crucial in cancer treatment. Evaluation of membrane permeability is a key metric for successful drug development. In this study, we have used in silico molecular models of lipid bilayers to explore the effect of phosphatidylserine (PS) exposure in cancer cells on membrane permeation of natural compounds Withaferin A (Wi-A), Withanone (Wi-N), Caffeic Acid Phenethyl Ester (CAPE) and Artepillin C (ARC). Molecular dynamics simulations were performed to compute permeability coefficients. The results indicated that the exposure of PS in cancer cell membranes facilitated the permeation of Wi-A, Wi-N and CAPE through a cancer cell membrane when compared to a normal cell membrane. In the case of ARC, PS exposure did not have a notable influence on its permeability coefficient. The presented data demonstrated the potential of PS exposure-based models for studying cancer cell selectivity of drugs.

Embedding a Membrane Protein into an Enveloped Artificial Viral Replica

Natural enveloped viruses, in which nucleocapsids are covered with lipid bilayers, contain membrane proteins on the outer surface that are involved in diverse functions, such as adhesion and infection of...

A synergy between mechanosensitive calcium- and membrane-binding mediates tension-sensing by C2-like domains

When nuclear membranes are stretched, the peripheral membrane enzyme cytosolic phospholipase A2 (cPLA2) binds via its calcium-dependent C2 domain (cPLA2-C2) and initiates bioactive lipid signaling and tissue inflammation. More than 150 C2-like domains are encoded in vertebrate genomes. How many of them are mechanosensors and quantitative relationships between tension and membrane recruitment remain unexplored, leaving a knowledge gap in the mechanotransduction field. In this study, we imaged the mechanosensitive adsorption of cPLA2 and its C2 domain to nuclear membranes and artificial lipid bilayers, comparing it to related C2-like motifs. Stretch increased the Ca2+ sensitivity of all tested domains, promoting half-maximal binding of cPLA2 at cytoplasmic resting-Ca2+ concentrations. cPLA2-C2 bound up to 50 times tighter to stretched than to unstretched membranes. Our data suggest that a synergy of mechanosensitive Ca2+ interactions and deep, hydrophobic membrane insertion enables cPLA2-C2 to detect stretched membranes with antibody-like affinity, providing a quantitative basis for understanding mechanotransduction by C2-like domains.