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1.
The Endoplasmic Reticulum-Plasma Membrane Junction: A Hub for Agonist Regulation of Ca2+ Entry.
Ong, HL, Ambudkar, IS
Cold Spring Harbor perspectives in biology. 2020;(2)
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Abstract
Stimulation of cell-surface receptors induces cytosolic Ca2+ ([Ca2+]i) increases that are detected and transduced by effector proteins for regulation of cell function. Intracellular Ca2+ release, via endoplasmic reticulum (ER) proteins inositol 1,4,5-trisphosphate receptors (IP3R) and ryanodine receptors (RyR), and Ca2+ influx, via store-operated Ca2+ entry (SOCE), contribute to the increase in [Ca2+]i The amplitude, frequency, and spatial characteristics of the [Ca2+]i increases are controlled by the compartmentalization of proteins into signaling complexes such as receptor-signaling complexes and SOCE complexes. Both complexes include protein and lipid components, located in the plasma membrane (PM) and ER. Receptor signaling initiates in the PM via phospholipase C (PLC)-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), and culminates with the activation of IP3R in the ER. Conversely, SOCE is initiated in the ER by Ca2+-sensing stromal interaction molecule (STIM) proteins, which then interact with PM channels Orai1 and TRPC1 to activate Ca2+ entry. This review will address how ER-PM junctions serve a central role in agonist regulation of SOCE.
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Review of Chitosan-Based Polymers as Proton Exchange Membranes and Roles of Chitosan-Supported Ionic Liquids.
Rosli, NAH, Loh, KS, Wong, WY, Yunus, RM, Lee, TK, Ahmad, A, Chong, ST
International journal of molecular sciences. 2020;(2)
Abstract
Perfluorosulphonic acid-based membranes such as Nafion are widely used in fuel cell applications. However, these membranes have several drawbacks, including high expense, non-eco-friendliness, and low proton conductivity under anhydrous conditions. Biopolymer-based membranes, such as chitosan (CS), cellulose, and carrageenan, are popular. They have been introduced and are being studied as alternative materials for enhancing fuel cell performance, because they are environmentally friendly and economical. Modifications that will enhance the proton conductivity of biopolymer-based membranes have been performed. Ionic liquids, which are good electrolytes, are studied for their potential to improve the ionic conductivity and thermal stability of fuel cell applications. This review summarizes the development and evolution of CS biopolymer-based membranes and ionic liquids in fuel cell applications over the past decade. It also focuses on the improved performances of fuel cell applications using biopolymer-based membranes and ionic liquids as promising clean energy.
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Membrane Activity and Channel Formation of the Adenylate Cyclase Toxin (CyaA) of Bordetella pertussis in Lipid Bilayer Membranes.
Knapp, O, Benz, R
Toxins. 2020;(3)
Abstract
The Gram-negative bacterium Bordetella pertussis is the cause of whooping cough. One of its pathogenicity factors is the adenylate cyclase toxin (CyaA) secreted by a Type I export system. The 1706 amino acid long CyaA (177 kDa) belongs to the continuously increasing family of repeat in toxin (RTX) toxins because it contains in its C-terminal half a high number of nine-residue tandem repeats. The protein exhibits cytotoxic and hemolytic activities that target primarily myeloid phagocytic cells expressing the αMβ2 integrin receptor (CD11b/CD18). CyaA represents an exception among RTX cytolysins because the first 400 amino acids from its N-terminal end possess a calmodulin-activated adenylate cyclase (AC) activity. The entry of the AC into target cells is not dependent on the receptor-mediated endocytosis pathway and penetrates directly across the cytoplasmic membrane of a variety of epithelial and immune effector cells. The hemolytic activity of CyaA is rather low, which may have to do with its rather low induced permeability change of target cells and its low conductance in lipid bilayer membranes. CyaA forms highly cation-selective channels in lipid bilayers that show a strong dependence on aqueous pH. The pore-forming activity of CyaA but not its single channel conductance is highly dependent on Ca2+ concentration with a half saturation constant of about 2 to 4 mM.
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Lipid composition of the cancer cell membrane.
Szlasa, W, Zendran, I, Zalesińska, A, Tarek, M, Kulbacka, J
Journal of bioenergetics and biomembranes. 2020;(5):321-342
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Abstract
Cancer cell possesses numerous adaptations to resist the immune system response and chemotherapy. One of the most significant properties of the neoplastic cells is the altered lipid metabolism, and consequently, the abnormal cell membrane composition. Like in the case of phosphatidylcholine, these changes result in the modulation of certain enzymes and accumulation of energetic material, which could be used for a higher proliferation rate. The changes are so prominent, that some lipids, such as phosphatidylserines, could even be considered as the cancer biomarkers. Additionally, some changes of biophysical properties of cell membranes lead to the higher resistance to chemotherapy, and finally to the disturbances in signalling pathways. Namely, the increased levels of certain lipids, like for instance phosphatidylserine, lead to the attenuation of the immune system response. Also, changes in lipid saturation prevent the cells from demanding conditions of the microenvironment. Particularly interesting is the significance of cell membrane cholesterol content in the modulation of metastasis. This review paper discusses the roles of each lipid type in cancer physiology. The review combined theoretical data with clinical studies to show novel therapeutic options concerning the modulation of cell membranes in oncology.
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Facile synthesis of a Co/Fe bi-MOFs/CNF membrane nanocomposite and its application in the degradation of tetrabromobisphenol A.
Hou, C, Chen, W, Fu, L, Zhang, S, Liang, C, Wang, Y
Carbohydrate polymers. 2020;:116731
Abstract
In this study, a sulfate radical-advanced oxidation process (SR-AOP) was proposed by utilizing a bimetallic Co/Fe metal-organic frameworks/cellulose nanofiber membrane (Co/Fe bi-MOFs/CNF) as a catalyst for TBBPA degradation. Sulfate radicals (SO4-) and hydroxyl radicals (OH·) were generated through the activation of peroxymonosulfate (PMS) by Co/Fe bi-MOFs/CNF. Co/Fe bi-MOFs/CNF was prepared by a facile solvothermal method and vacuum filtration. CNF acted as a natural substrates material to relieve the agglomeration of loaded MOFs. Additionally the composite membranes was easily separated from the reaction solution. The properties of the composite materials and the main factors that influenced TBBPA degradation were elucidated in detail, along with the TBBPA degradation intermediates, recyclability, and TBBPA degradation pathway. Almost 100 % of TBBPA was degraded within 30 min under optimal conditions, and the rate constant was determined to be 0.764 min-1. Furthermore, the degradation rate of the composite membrane was 60 % after 4 cycles.
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Predicting the unexpected in stomatal gas exchange: not just an open-and-shut case.
Klejchová, M, Hills, A, Blatt, MR
Biochemical Society transactions. 2020;(3):881-889
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Abstract
Plant membrane transport, like transport across all eukaryotic membranes, is highly non-linear and leads to interactions with characteristics so complex that they defy intuitive understanding. The physiological behaviour of stomatal guard cells is a case in point in which, for example, mutations expected to influence stomatal closing have profound effects on stomatal opening and manipulating transport across the vacuolar membrane affects the plasma membrane. Quantitative mathematical modelling is an essential tool in these circumstances, both to integrate the knowledge of each transport process and to understand the consequences of their manipulation in vivo. Here, we outline the OnGuard modelling environment and its use as a guide to predicting the emergent properties arising from the interactions between non-linear transport processes. We summarise some of the recent insights arising from OnGuard, demonstrate its utility in interpreting stomatal behaviour, and suggest ways in which the OnGuard environment may facilitate 'reverse-engineering' of stomata to improve water use efficiency and carbon assimilation.
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Porins and small-molecule translocation across the outer membrane of Gram-negative bacteria.
Vergalli, J, Bodrenko, IV, Masi, M, Moynié, L, Acosta-Gutiérrez, S, Naismith, JH, Davin-Regli, A, Ceccarelli, M, van den Berg, B, Winterhalter, M, et al
Nature reviews. Microbiology. 2020;(3):164-176
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Abstract
Gram-negative bacteria and their complex cell envelope, which comprises an outer membrane and an inner membrane, are an important and attractive system for studying the translocation of small molecules across biological membranes. In the outer membrane of Enterobacteriaceae, trimeric porins control the cellular uptake of small molecules, including nutrients and antibacterial agents. The relatively slow porin-mediated passive uptake across the outer membrane and active efflux via efflux pumps in the inner membrane creates a permeability barrier. The synergistic action of outer membrane permeability, efflux pump activities and enzymatic degradation efficiently reduces the intracellular concentrations of small molecules and contributes to the emergence of antibiotic resistance. In this Review, we discuss recent advances in our understanding of the molecular and functional roles of general porins in small-molecule translocation in Enterobacteriaceae and consider the crucial contribution of porins in antibiotic resistance.
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Plasma Membrane Domain Patterning and Self-Reinforcing Polarity in Arabidopsis.
Marhava, P, Aliaga Fandino, AC, Koh, SWH, Jelínková, A, Kolb, M, Janacek, DP, Breda, AS, Cattaneo, P, Hammes, UZ, Petrášek, J, et al
Developmental cell. 2020;(2):223-235.e5
Abstract
Cell polarity is a key feature in the development of multicellular organisms. For instance, asymmetrically localized plasma-membrane-integral PIN-FORMED (PIN) proteins direct transcellular fluxes of the phytohormone auxin that govern plant development. Fine-tuned auxin flux is important for root protophloem sieve element differentiation and requires the interacting plasma-membrane-associated BREVIS RADIX (BRX) and PROTEIN KINASE ASSOCIATED WITH BRX (PAX) proteins. We observed "donut-like" polar PIN localization in developing sieve elements that depends on complementary, "muffin-like" polar localization of BRX and PAX. Plasma membrane association and polarity of PAX, and indirectly BRX, largely depends on phosphatidylinositol-4,5-bisphosphate. Consistently, mutants in phosphatidylinositol-4-phosphate 5-kinases (PIP5Ks) display protophloem differentiation defects similar to brx mutants. The same PIP5Ks are in complex with BRX and display "muffin-like" polar localization. Our data suggest that the BRX-PAX module recruits PIP5Ks to reinforce PAX polarity and thereby the polarity of all three proteins, which is required to maintain a local PIN minimum.
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Role of the lipid bilayer in outer membrane protein folding in Gram-negative bacteria.
Horne, JE, Brockwell, DJ, Radford, SE
The Journal of biological chemistry. 2020;(30):10340-10367
Abstract
β-Barrel outer membrane proteins (OMPs) represent the major proteinaceous component of the outer membrane (OM) of Gram-negative bacteria. These proteins perform key roles in cell structure and morphology, nutrient acquisition, colonization and invasion, and protection against external toxic threats such as antibiotics. To become functional, OMPs must fold and insert into a crowded and asymmetric OM that lacks much freely accessible lipid. This feat is accomplished in the absence of an external energy source and is thought to be driven by the high thermodynamic stability of folded OMPs in the OM. With such a stable fold, the challenge that bacteria face in assembling OMPs into the OM is how to overcome the initial energy barrier of membrane insertion. In this review, we highlight the roles of the lipid environment and the OM in modulating the OMP-folding landscape and discuss the factors that guide folding in vitro and in vivo We particularly focus on the composition, architecture, and physical properties of the OM and how an understanding of the folding properties of OMPs in vitro can help explain the challenges they encounter during folding in vivo Current models of OMP biogenesis in the cellular environment are still in flux, but the stakes for improving the accuracy of these models are high. OMP folding is an essential process in all Gram-negative bacteria, and considering the looming crisis of widespread microbial drug resistance it is an attractive target. To bring down this vital OMP-supported barrier to antibiotics, we must first understand how bacterial cells build it.
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Hydrogen peroxide permeability of cellular membranes in insulin-producing cells.
Laporte, A, Lortz, S, Schaal, C, Lenzen, S, Elsner, M
Biochimica et biophysica acta. Biomembranes. 2020;(2):183096
Abstract
Hydrogen peroxide (H2O2) plays a central role in redox signalling and in oxidative stress-mediated cell death. It is generated through multiple mechanisms at various intracellular sites. Due to its chemical stability it can reach distant sites of action. However, its hydrophilicity can hamper lipid membrane passage. We therefore studied the kinetics of H2O2 diffusion through subcellular membranes employing the H2O2 biosensor HyPer in insulin-producing RINm5F cells. Plasma- and ER-membrane-bound HyPer sensors facing the cytosolic compartment reacted twice as fast to H2O2 compared to sensors expressed in peroxisomes and mitochondria. Overexpression of the H2O2-inactivating enzyme catalase in the ER-lumen and in the peroxisomes retarded the reaction time of HyPer, both localised within the peroxisomes as well as at the cytosolic surface of the ER. The unsaturated fatty acid oleic acid did not affect the reaction of the peroxisomal HyPer sensor to H2O2, while the saturated fatty acid palmitic acid accelerated its reaction time to H2O2 in this organelle. The results show that the plasma-, peroxisomal, and mitochondrial membrane of insulin-producing RINm5F cells are permeable for H2O2. Nonetheless, the organelle membranes retard H2O2 diffusion due to a barrier function of the lipid membrane, as documented by retarded reaction times of the intraorganellar sensors. Accelerated decomposition of H2O2 by catalase, expressed in the peroxisomes or the ER, further retarded the HyPer sensor reaction time. The results show that redox signalling and oxidative stress-mediated toxicity are crucially dependent on physicochemical membrane properties and antioxidative defence mechanisms in health and disease.