Lipid Bilayer Of Plasma Membrane Research Articles

Emerging Role of Noncovalent Interactions and Disulfide Bond Formation in the Cellular Uptake of Small Molecules and Proteins.

Intracellular delivery of proteins is an important barrier in the development of strategies to deliver functional proteins and protein therapeutics into the cells to realize their full potential in biotechnology, biomedicine, cell-based therapies, and gene editing protein systems. Most of the intracellular protein delivery strategies involve the conjugation of cell penetrating peptides to enable and enhance the permeability of plasma membrane of mammalian cells to allow proteins to enter cytosol. Small molecules conjugations such as (p-methylphenyl) glycine, pyrenebutyrate and cysteines are used for the same purpose. The molecular level interactions are governed mostly by ionic (cationic/anionic), covalent and non-covalent interactions with various molecular entities of glycocalyx matrix on plasma membrane lipid bilayer. Although the role of non-covalent interactions is not fully understood, it is intriguing to see the recent advances in the non-covalent interaction-based strategies of intracellular delivery of small molecules and proteins into mammalian cells. These are achieved by simple modification of proteins' surface with chemical moieties which can form non-covalent interactions other than hydrogen bonding. In this review, we describe the recent advances and the mechanistic aspects of intracellular delivery and role of non-covalent interactions during the cellular uptake of proteins and small molecules.

Rabies virus-mimicking liposomes for targeted gene therapy in Alzheimer’s disease

RNA interference (RNAi) harbors significant potential for treating neurological disorders; nevertheless, limited efficacy has been discerned. The presence of barriers within the central nervous system, coupled with the inherent instability of nucleic acids within biological conditions, poses formidable challenges in advancing effective gene delivery strategies. In this study, we designed and prepared a virus-mimic non-viral gene vector, rabies virus glycoprotein (RVG29)-decorated liposome (f(Lipo)-RVG29), to deliver small interfering RNAs to the brain. Alzheimer’s disease (AD) was chosen as a model of neurodegenerative disease in this context, and b-site APP cleaving enzyme silencing siRNA (siBACE1) was used. The developed liposomal delivery system has a particle size of under 80 nm with a spherical shape, positive zeta potential, and the ability to protect siRNA against nucleases. In vitro studies demonstrate that functionalizing the cationic liposome by the RVG29 targeting ligand significantly enhances the effectiveness of gene delivery and silencing. Examination through ex vivo imaging illustrates an increased deposition of fluorescent-labeled f(Lipo)-RVG29 within brain tissue after 12 h post application. Additionally, the in vivo delivery of f(Lipo)-RVG29 carrying siRNA has substantially suppressed BACE1 expression at both mRNA and protein levels within the brain tissue. Our results suggest that the developed non-viral vector could be a promising gene carrier system combining the synergistic effect of virus-mimic RVG29 ligand with bioinspired liposome that imitates the natural lipid bilayers of cell membranes for brain-targeted RNAi therapeutics.

An Overview of Multifaceted Applications and the Future Prospects of Glyceroglycolipids in Plants.

Glyceroglycolipids (GGLs) are a class of lipid molecules that contain a glycerol backbone and one or more carbohydrate moieties, giving them amphipathic properties with both hydrophilic and hydrophobic regions. This amphipathic nature is fundamental for composing cell membrane lipid bilayers. These compounds are primarily distributed on the inner chloroplast membranes of plants and exhibit a unique structure with numerous biological activities. Moreover, GGLs play a pivotal role in photosynthesis and energy conversion in plants and effectively respond to environmental stressors. This Review discusses the distribution, synthesis pathways, and functions of GGLs in plants and describes the recent updates on various methods for extracting, isolating, and identifying GGLs. Finally, this Review discusses the biological activities of plant GGLs, including their anti-inflammatory, antiviral, and anticancer properties, and highlights their potential applications in the fields of pharmaceuticals, food, and cosmetics. This Review provides insights into GGLs, offering research support for the application of these natural molecules in the realm of holistic health.

Adaptation of the maize seedling seminal roots to srought: Essential role of plasma membrane H+-ATPases activity

To understand how maize plants adapt to drought, this study examines the role of plasma membrane proton pumps in root growth. This study delves into the physiological mechanisms through which maize plants respond to drought conditions, with a particular emphasis on elucidating the crucial role played by plasma membrane proton pumps in facilitating adaptive changes in root growth. Our results underscore the indispensable nature of these pumps in orchestrating precise modulation of root growth patterns during drought stress, highlighting their profound significance in stress responses. Additionally, the study reveals that osmotic stress alters lipid profiles in the plasma membrane, potentially impacting its functioning and the activity of membrane proteins. To understand the role of plasma membrane (PM) H<sup>+</sup>-ATPases in the adaptative response to osmotic stress and in the regulation of root growth in maize, we studied the gene expression and enzyme activity of PM H<sup>+</sup>-ATPases, as well as the changes in plant biomass and total root growth, in the seedlings of two maize cultivars: the drought-tolerant Calo cultivar and the drought-sensitive Abelardo. The seedlings were exposed to simulated drought for 24 h (treatment with 20% PEG). The enzyme activity and gene expression of the <i>MHA4</i> H<sup>+</sup>-ATPase increased in the Calo variety but declined in Abelardo plants treated with PEG. The growth of roots in Abelardo plants exposed to 24 h of PEG treatment was reduced to almost 50% of the control. Conversely, for the Calo cultivar, there was no remarkable morpho-physiological difference between the roots of stressed and non-stressed plants. Therefore, the activity of the PM H<sup>+</sup>-ATPase seems to be an important factor for proper root growth during the adaptation of maize to drought. In addition, osmotic stress also induced changes in the levels of saturated polyisoprenoid alcohols in the plasma membrane fraction of maize roots. The increased levels of this class of lipids might modulate the physico-chemical properties of the PM lipid bilayer and thus affect its functioning and modify the activity of membrane proteins, such as PM H<sup>+</sup>-ATPases.

A novel missense variant in ATP11C is associated with reduced red blood cell phosphatidylserine flippase activity and mild hereditary hemolytic anemia.

Adenosine Triphosphatase (ATPase) Phospholipid Transporting 11C gene (ATP11C) encodes the major phosphatidylserine (PS) flippase in human red blood cells (RBCs). Flippases actively transport phospholipids (e.g., PS) from the outer to the inner leaflet to establish and maintain phospholipid asymmetry of the lipid bilayer of cell membranes. This asymmetry is crucial for survival since externalized PS triggers phagocytosis by splenic macrophages. Here we report on pathophysiological consequences of decreased flippase activity, prompted by a patient with hemolytic anemia and hemizygosity for a novel c.2365C > T p.(Leu789Phe) missense variant in ATP11C. ATP11C protein expression was strongly reduced by 58% in patient-derived RBC ghosts. Furthermore, functional characterization showed only 26% PS flippase activity. These results were confirmed by recombinant mutant ATP11C protein expression in HEK293T cells, which was decreased to 27% compared to wild type, whereas PS-stimulated ATPase activity was decreased by 57%. Patient RBCs showed a mild increase in PS surface exposure when compared to control RBCs, which further increased in the most dense RBCs after RBC storage stress. The increase in PS was not due to higher global membrane content of PS or other phospholipids. In contrast, membrane lipid lateral distribution showed increased abundance of cholesterol-enriched domains in RBC low curvature areas. Finally, more dense RBCs and subtle changes in RBC morphology under flow hint toward alterations in flow behavior of ATP11C-deficient RBCs. Altogether, ATP11C deficiency is the likely cause of hemolytic anemia in our patient, thereby underlining the physiological role and relevance of this flippase in human RBCs.

Resveratrol and 2-Ethyl-6-Methyl-3-Hydroxypiridine N-Acetyl Cysteinate as Protecting Agents upon the Stress Exposure.

The increased generation of reactive oxygen species (ROS) by mitochondria under stress conditions leads to lipid peroxidation (LPO) as a consequence of the ROS interactions with polyunsaturated fatty acids in the lipid bilayer of cell membranes, causing their damage. It was assumed that chemical preparations that reduce the excessive ROS generation by mitochondria should exhibit protecting properties under oxidative-stress conditions. In this context, the antioxidants resveratrol (RSV) and 2-ethyl-6-methyl-3-hydroxypyridine N-acetylcysteinate (NAC-3-HP) were examined as potential chemical protectors upon the exposure to stress, able to maintain the functional state of mitochondria.

A Novel Two-Component Bacteriocin, Acidicin P, and Its Key Residues for Inhibiting Listeria monocytogenes by Targeting the Cell Membrane.

Listeria monocytogenes is an important pathogen which easily contaminates food and causes fatal systemic infections in human. Bacteriocins have received much attention regarding their natural methods of controlling health-related pathogens. Here, we investigated and characterized a novel two-component bacteriocin named acidicin P from Pediococcus acidilactici LAC5-17. Acidicin P showed obvious antimicrobial activity to L. monocytogenes. Through a sequence similarity network analysis for two-component bacteriocin precursors mined in the RefSeq database, acidicin P was observed to belong to an unusual group of two-component bacteriocins. Acidicin P contains two peptides designated Adpα and Adpβ which are assessed to interact with each other and form a helical dimer structure which can be inserted into the lipid bilayer of target cell membrane. We demonstrate that A5, N7, and G9 in the A5xxxG9 motif of Adpα and S16, R19, and G20 in the S16xxxG20 motif of Adpβ played crucial roles in stabilizing the helix-helix interaction of Adpα and Adpβ and were essential for the antilisterial activity of acidicin P by site-directed mutagenesis. A positive residue, R14, in Adpα and a negative residue, D12, in Adpβ are also important for acidicin P to fight against L. monocytogenes. These key residues are supposed to form hydrogen bonding, which is crucial for the interaction of Adpα and Adpβ. Furthermore, acidicin P induces severe permeabilization and depolarization of the cytoplasmic membrane and causes dramatic changes in L. monocytogenes cell morphology and ultrastructure. Acidicin P has the potential to be applied to inhibit L. monocytogenes efficiently both in the food industry and medical treatments. IMPORTANCE L. monocytogenes can cause widespread food contamination and severe human listeriosis, which amount to a large proportion of the public health and economic burdens. Today, L. monocytogenes is usually treated with chemical compounds in the food industry or antibiotics for human listeriosis. Natural and safe antilisterial agents are urgently required. Bacteriocins are natural antimicrobial peptides that have comparable narrow antimicrobial spectra and are attractive potentials for precision therapy for pathogen infection. In this work, we discover a novel two-component bacteriocin designated acidicin P, which shows obvious antilisterial activity. We also identify the key residues in both peptides of acidicin P and demonstrate that acidicin P is inserted into the target cell membrane and disrupts the cell envelop to inhibit the growth of L. monocytogenes. We believe that acidicin P is a promising lead for further development as an antilisterial drug.

Newly Developed Di-Block Copolymer-Based Cell Membrane Stabilizers Protect Mouse Coronary Artery Endothelial Cells against Hypoxia/Reoxygenation Injury.

Reperfusion after ischemia causes additional cellular damage, known as reperfusion injury, for which there is still no effective remedy. Poloxamer (P)188, a tri-block copolymer-based cell membrane stabilizer (CCMS), has been shown to provide protection against hypoxia/reoxygenation (HR) injury in various models by reducing membrane leakage and apoptosis and improving mitochondrial function. Interestingly, substituting one of its hydrophilic poly-ethylene oxide (PEO) blocks with a (t)ert-butyl terminus added to the hydrophobic poly-propylene oxide (PPO) block yields a di-block compound (PEO-PPOt) that interacts better with the cell membrane lipid bi-layer and exhibits greater cellular protection than the gold standard tri-block P188 (PEO75-PPO30-PEO75). For this study, we custom-made three different new di-blocks (PEO113-PPO10t, PEO226-PPO18t and PEO113-PPO20t) to systemically examine the effects of the length of each polymer block on cellular protection in comparison to P188. Cellular protection was assessed by cell viability, lactate dehydrogenase release, and uptake of FM1-43 in mouse artery endothelial cells (ECs) following HR injury. We found that di-block CCMS were able to provide the same or better EC protection than P188. Our study provides the first direct evidence that custom-made di-block CCMS can be superior to P188 in improving EC membrane protection, raising their potential in treating cardiac reperfusion injury.

Molecular Modeling of Viral Type I Fusion Proteins: Inhibitors of Influenza Virus Hemagglutinin and the Spike Protein of Coronavirus.

The fusion of viral and cell membranes is one of the basic processes in the life cycles of viruses. A number of enveloped viruses confer fusion of the viral envelope and the cell membrane using surface viral fusion proteins. Their conformational rearrangements lead to the unification of lipid bilayers of cell membranes and viral envelopes and the formation of fusion pores through which the viral genome enters the cytoplasm of the cell. A deep understanding of all the stages of conformational transitions preceding the fusion of viral and cell membranes is necessary for the development of specific inhibitors of viral reproduction. This review systematizes knowledge about the results of molecular modeling aimed at finding and explaining the mechanisms of antiviral activity of entry inhibitors. The first section of this review describes types of viral fusion proteins and is followed by a comparison of the structural features of class I fusion proteins, namely influenza virus hemagglutinin and the S-protein of the human coronavirus.

Endosomal escape of RNA therapeutics: How do we solve this rate-limiting problem?

With over 15 FDA approved drugs on the market and numerous ongoing clinical trials, RNA therapeutics, such as small interfering RNAs (siRNAs) and antisense oligonucleotides (ASOs), have shown great potential to treat human disease. Their mechanism of action is based entirely on the sequence of validated disease-causing genes without the prerequisite knowledge of protein structure, activity or cellular location. In contrast to small molecule therapeutics that passively diffuse across the cell membrane's lipid bilayer, RNA therapeutics are too large, too charged, and/or too hydrophilic to passively diffuse across the cellular membrane and instead are taken up into cells by endocytosis. However, endosomes are also composed of a lipid bilayer barrier that results in endosomal capture and retention of 99% of RNA therapeutics with 1% or less entering the cytoplasm. Although this very low level of endosomal escape has proven sufficient for liver and some CNS disorders, it is insufficient for the vast majority of extra-hepatic diseases. Unfortunately, there are currently no acceptable solutions to the endosomal escape problem. Consequently, before RNA therapeutics can be used to treat widespread human disease, the rate-limiting delivery problem of endosomal escape must be solved in a nontoxic manner.

Plasma membrane lipid bilayer is druggable: Selective delivery of gemcitabine-squalene nano-medicine to cancer cells

Up to now the lipid bilayers were rarely considered as targets in cancer therapy despite pronounced differences in lipid composition between plasma membranes of benign and malignant cells. In this study we demonstrate that the lipid bilayer of the plasma membrane is druggable and suitable for facilitating selective delivery of amphiphilic gemcitabine-squalene nanomedicines to cancer cells. Data from radioactive assays, fluorescent membrane probes and molecular dynamics simulations provide evidence of selective accumulation of gemcitabine-squalene in the plasma membranes with disrupted lipid asymmetry and its subsequent preferential uptake by malignant cells. This causes pronounced cytotoxicity on cancer cells in comparison to their benign counterparts originating from the same tissue.

Two types of type IV P-type ATPases independently re-establish the asymmetrical distribution of phosphatidylserine in plasma membranes

Phospholipids are asymmetrically distributed between the lipid bilayer of plasma membranes in which phosphatidylserine (PtdSer) is confined to the inner leaflet. ATP11A and ATP11C, type IV P-Type ATPases in plasma membranes, flip PtdSer from the outer to the inner leaflet, but involvement of other P4-ATPases is unclear. We herein demonstrated that once PtdSer was exposed on the cell surface of ATP11A−/−ATP11C−/− mouse T cell line (W3), its internalization to the inner leaflet of plasma membranes was negligible at 15 °C. However, ATP11A−/−ATP11C−/− cells internalized the exposed PtdSer at 37 °C, a temperature at which trafficking of intracellular membranes was active. In addition to ATP11A and 11C, W3 cells expressed ATP8A1, 8B2, 8B4, 9A, 9B, and 11B, with ATP8A1 and ATP11B being present at recycling endosomes. Cells deficient in four P4-ATPases (ATP8A1, 11A, 11B, and 11C) (QKO) did not constitutively expose PtdSer on the cell surface but lost the ability to re-establish PtdSer asymmetry within 1 hour, even at 37 °C. The expression of ATP11A or ATP11C conferred QKO cells with the ability to rapidly re-establish PtdSer asymmetry at 15 °C and 37 °C, while cells expressing ATP8A1 or ATP11B required a temperature of 37 °C to achieve this function, and a dynamin inhibitor blocked this process. These results revealed that mammalian cells are equipped with two independent mechanisms to re-establish its asymmetry: the first is a rapid process involving plasma membrane flippases, ATP11A and ATP11C, while the other is mediated by ATP8A1 and ATP11B, which require an endocytosis process.

Amyloid fibrils act as a reservoir of soluble oligomers, the main culprits in protein deposition diseases.

Amyloid fibril formation plays a central role in the pathogenesis of a number of neurodegenerative diseases, including Alzheimer and Parkinson diseases. Transient prefibrillar oligomers forming during the aggregation process, exhibiting a small size and a large hydrophobic surface, can aberrantly interact with a number of molecular targets on neurons, including the lipid bilayer of plasma membranes, resulting in a fatal outcome for the cells. By contrast, the mature fibrils, despite presenting generally a high hydrophobic surface, are endowed with a low diffusion rate and poorly penetrate the interior of the lipid bilayer. However, increasing evidence shows that both intracellular α-synuclein fibrils, as well and as extracellular amyloid-β and β2-microglobulin fibrils, can release oligomers over time that quickly diffuse to reach the membrane of the neighboring cells. The persistent leakage of harmful oligomers from fibrils triggers an ongoing cascade of events resulting in a sustained injury to neurons and glia and also provides aggregates with the ability to cross biological membranes and diffuse between cells or cellular compartments.

Piezo1: opening the way to preventing muscle atrophy.

The loss of skeletal muscle mass and size, or muscle atrophy, is a common human experience, linked to disability, for which there are no widely accepted pharmacological therapies. Piezo1 is a mechanosensitive cation channel that opens upon alteration of the plasma membrane lipid bilayer, such as through increased membrane tension. In this issue of the JCI, Hirata et al. identified Piezo1 and its downstream effectors, Krüppel-like factor 15 (KLF15) and interleukin-6 (IL-6), as an important signaling pathway in a murine model of disuse atrophy. Through genetic and pharmacological modulation of the pathway, the authors demonstrated that immobilization resulted in downregulation of Piezo1 and basal intracellular calcium concentration ([Ca2+]i), increasing expression of Klf15 and its downstream target Il6 and thereby inducing muscle atrophy. Piezo1 has been considered a therapeutic target for diverse disorders, including atherosclerosis and kidney fibrosis, and with this publication should now also be considered a viable target for disuse atrophy.

Cancer’s camouflage: Microvesicle shedding from cholesterol-rich tumor plasma membranes might blindfold first-responder immunosurveillance strategies

Intermediary metabolism of tumors is characterized, in part, by a dysregulation of the cholesterol biosynthesis pathway at its rate-controlling enzyme providing the molecular basis for tumor membranes (mitochondria, plasma membrane) to become enriched with cholesterol (Bloch, 1965; Feo et al., 1975; Brown and Goldstein, 1980; Goldstein and Brown, 1990). Cholesterol enriched tumor mitochondria manifest preferential citrate export, thereby providing a continuous supply of substrate precursor for the tumor’s dysregulated cholesterogenesis via a “truncated” Krebs/TCA cycle (Kaplan et al., 1986; Coleman et al., 1997). Proliferating tumors shed elevated amounts of plasma membrane-derived extracellular vesicles (pmEV) compared with normal tissues (van Blitterswijk et al., 1979; Black, 1980). Coordination of these metabolic phenomena in tumors supports the enhanced intercalation of cholesterol within the plasma membrane lipid bilayer’s cytoplasmic face, the promotion of outward protrusions from the plasma membrane, and the evolution of cholesterol enriched pmEV. The pmEV shed by tumors possess elevated cholesterol and concentrated cell surface antigen clusters found on the tumor cells themselves (Kim et al., 2002). Upon exfoliation, saturation of the extracellular milieu with tumor-derived pmEV could allow early onset mammalian immune surveillance mechanisms to become “blind” to an evolving cancer and lose their ability to detect and initiate strategies to destroy the cancer. However, a molecular mechanism is lacking that would help explain how cholesterol enrichment of the pmEV inner lipid bilayer might allow the tumor cell to evade the host immune system. We offer a hypothesis, endorsed by published mathematical modeling of biomembrane structure as well as by decades of in vivo data with diverse cancers, that a cholesterol enriched inner bilayer leaflet, coupled with a logarithmic expansion in surface area of shed tumor pmEV load relative to its derivative cancer cell, conspire to force exposure of otherwise unfamiliar membrane integral protein domains as antigenic epitopes to the host’s circulating immune surveillance system, allowing the tumor cells to evade destruction. We provide elementary numerical estimations comparing the amount of pmEV shed from tumor versus normal cells.

Investigation of Biofouling and Its Effect on the Properties of Basalt Fiber Reinforced Plastic Rebars Exposed to Extremely Cold Climate Conditions.

For the first time, the possibility of penetration of mold fungi mycelium and spore-forming bacteria into the structure of basalt fiber reinforced plastic rebars has been shown in laboratory and field experiments. Biological contamination at the “fiber-binding” border reveals areas of swelling and penetration of mold fungi mycelium and bacterial spore cells into the binder component. After the exposure of samples at extremely low temperatures, strains of mold fungi of the genus Aspergillus were also isolated from the surface of the rebars. Additionally, spore-forming bacteria of the genus Bacillus immobilized for samples from two years ago. This indicates the high viability of immobilized strains in cold climates. Aboriginal microflora isolated by the enrichment culture technique from the samples was represented by: actinobacteria of the genera Nocardia and Streptomyces; yeast of the genus Rhodotorula; and mold fungi of the genus Penicillium. It was shown that the enrichment culture technique is a highly informative method of diagnosing the bio-infection of polymer composite materials during their operation in extremely low temperatures. The metabolic activity of the cells of cryophilic microorganisms isolated from experimental samples of basalt fiber reinforced plastic rebars was associated with the features of the enzymes and fatty acid composition of the lipid bilayer of cell membranes. In the case of temperature conditions when conventional (mesophilic) microorganisms stop developing vegetative cells, the process of transition of the lipid bilayer of cell membranes into a gel-like state was activated. This transition of the lipid bilayer to a gel-like state allowed the prevention of crystallization and death of the microbial cell when the ambient temperature dropped to negative values and as a result, after thawing, growth resumed and the metabolic activity of the microorganisms was restored. Studies have been carried out on the effect of biodepletion on the elastic strength characteristics, porosity and monolithicity of these materials, while at the same time, after a two year exposure, the strength preservation coefficient was k = 0.82 and the porosity increased by more than two times. The results show that the selected strains affect the properties of polymeric materials in cold climates in relation to the organic components in the structure of polymer composites.

The good and the bad of cell membrane electroporation.

Electroporation is used to increase the permeability of the cell membrane through high-voltage electric pulses. Nowadays, it is widely used in different areas, such as medicine, biotechnology, and the food industry. Electroporation induces the formation of hydrophilic pores in the lipid bilayer of cell membranes, to allow the entry or exit of molecules that cannot otherwise cross this hydrophobic barrier. In this article, we critically review the basic principles of electroporation, along with the advantages and drawbacks of this method. We discuss the effects of electroporation on the key components of biological membranes, as well as the main applications of this procedure in medicine, such as electrochemotherapy, gene electrotransfer, and tissue ablation. Finally, we define the most relevant challenges of this promising area of research.

The role of Globo H and SSEA-4 in the development and progression of cancer, and their potential as therapeutic targets.

Glycans, chains of sugar molecules found conjugated to cell proteins and lipids, contribute to their growth, movement and differentiation. Aberrant glycosylation is a hallmark of several medical conditions including tumorigenesis. Glycosphingolipids (GSLs), consisting of glycans conjugated to a lipid (ceramide) core, are found in the lipid bilayer of eukaryotic cell membranes. GSLs, play an active role in cell processes. Several GSLs are expressed by human embryonic stem cells and have been found to be overexpressed in several types of cancer. In this review, we discuss the data, hypotheses and perspectives related to the GSLs Globo H and SSEA-4.

Dynamic Role of Phospholipases A2 in Health and Diseases in the Central Nervous System.

Phospholipids are major components in the lipid bilayer of cell membranes. These molecules are comprised of two acyl or alkyl groups and different phospho-base groups linked to the glycerol backbone. Over the years, substantial interest has focused on metabolism of phospholipids by phospholipases and the role of their metabolic products in mediating cell functions. The high levels of polyunsaturated fatty acids (PUFA) in the central nervous system (CNS) have led to studies centered on phospholipases A2 (PLA2s), enzymes responsible for cleaving the acyl groups at the sn-2 position of the phospholipids and resulting in production of PUFA and lysophospholipids. Among the many subtypes of PLA2s, studies have centered on three major types of PLA2s, namely, the calcium-dependent cytosolic cPLA2, the calcium-independent iPLA2 and the secretory sPLA2. These PLA2s are different in their molecular structures, cellular localization and, thus, production of lipid mediators with diverse functions. In the past, studies on specific role of PLA2 on cells in the CNS are limited, partly because of the complex cellular make-up of the nervous tissue. However, understanding of the molecular actions of these PLA2s have improved with recent advances in techniques for separation and isolation of specific cell types in the brain tissue as well as development of sensitive molecular tools for analyses of proteins and lipids. A major goal here is to summarize recent studies on the characteristics and dynamic roles of the three major types of PLA2s and their oxidative products towards brain health and neurological disorders.

Biophysical characterisation of SMALPs.

Membrane proteins such as receptors, ion channels and transport proteins are important drug targets. The structure-based study of membrane proteins is challenging, especially when the target protein contains both soluble and insoluble domains. Most membrane proteins are insoluble in aqueous solvent and embedded in the plasma membrane lipid bilayer, which significantly complicates biophysical studies. Poly(styrene-co-maleic acid) (SMA) and other polymer derivatives are increasingly common solubilisation agents, used to isolate membrane proteins stabilised in their native lipid environment in the total absence of detergent. Since the initial report of SMA-mediated solubilisation, and the formation of SMA lipid particles (SMALPs), this technique can directly isolate therapeutic targets from biological membranes, including G-protein coupled receptors (GPCRs). SMA now allows biophysical and structural analyses of membrane proteins in solution that was not previously possible. Here, we critically review several existing biophysical techniques compatible with SMALPs, with a focus on hydrodynamic analysis, microcalorimetric analysis and optical spectroscopic techniques.