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1.
Structural Basis and Functional Implications of the Membrane Pore-Formation Mechanisms of Bacterial Pore-Forming Toxins.
Mondal, AK, Sreekumar, A, Kundu, N, Kathuria, R, Verma, P, Gandhi, S, Chattopadhyay, K
Advances in experimental medicine and biology. 2018;:281-291
Abstract
Pore-forming toxins (PFTs) are a distinct class of membrane-damaging protein toxins documented in a wide array of life forms ranging from bacteria to humans. PFTs are known to act as potent virulence factors of the bacterial pathogens. Bacterial PFTs are, in general, secreted as water-soluble molecules, which upon encountering target host cells assemble into transmembrane oligomeric pores, thus leading to membrane permeabilization and cell death. Interaction of the PFTs with the target host cells can also lead to plethora of cellular responses having critical implications for the bacterial pathogenesis processes, host-pathogen interactions, and host immunity. In this review, we present an overview of our current understanding of the structural aspects of the membrane pore-formation processes employed by the bacterial PFTs. We also discuss the functional implications of the PFT mode of actions, in terms of eliciting diverse cellular responses.
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2.
A Delicate Connection: c-di-AMP Affects Cell Integrity by Controlling Osmolyte Transport.
Commichau, FM, Gibhardt, J, Halbedel, S, Gundlach, J, Stülke, J
Trends in microbiology. 2018;(3):175-185
Abstract
Bacteria use second-messenger molecules to adapt to their environment. Several second messengers, among them cyclic di-AMP (c-di-AMP), have been discovered and intensively studied. Interestingly, c-di-AMP is essential for growth of Gram-positive bacteria such as Bacillus subtilis, Listeria monocytogenes, and Staphylococcus aureus. Many studies demonstrated that perturbation of c-di-AMP metabolism affects the integrity of the bacterial cell envelope. Therefore, it has been assumed that the nucleotide is essential for proper cell envelope synthesis. In this Opinion paper, we propose that the cell envelope phenotypes caused by perturbations of c-di-AMP metabolism can be interpreted differently: c-di-AMP might indirectly control cell envelope integrity by modulating the turgor, a physical variable that needs to be tightly adjusted. We also discuss open questions related to c-di-AMP metabolism that need to be urgently addressed by future studies.
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3.
Plant Endomembrane Dynamics: Studies of K+/H+ Antiporters Provide Insights on the Effects of pH and Ion Homeostasis.
Sze, H, Chanroj, S
Plant physiology. 2018;(3):875-895
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Abstract
Plants remodel their cells through the dynamic endomembrane system. Intracellular pH is important for membrane trafficking, but the determinants of pH homeostasis are poorly defined in plants. Electrogenic proton (H+) pumps depend on counter-ion fluxes to establish transmembrane pH gradients at the plasma membrane and endomembranes. Vacuolar-type H+-ATPase-mediated acidification of the trans-Golgi network is crucial for secretion and membrane recycling. Pump and counter-ion fluxes are unlikely to fine-tune pH; rather, alkali cation/H+ antiporters, which can alter pH and/or cation homeostasis locally and transiently, are prime candidates. Plants have a large family of predicted cation/H+ exchangers (CHX) of obscure function, in addition to the well-studied K+(Na+)/H+ exchangers (NHX). Here, we review the regulation of cytosolic and vacuolar pH, highlighting the similarities and distinctions of NHX and CHX members. In planta, alkalinization of the trans-Golgi network or vacuole by NHXs promotes membrane trafficking, endocytosis, cell expansion, and growth. CHXs localize to endomembranes and/or the plasma membrane and contribute to male fertility, pollen tube guidance, pollen wall construction, stomatal opening, and, in soybean (Glycine max), tolerance to salt stress. Three-dimensional structural models and mutagenesis of Arabidopsis (Arabidopsis thaliana) genes have allowed us to infer that AtCHX17 and AtNHX1 share a global architecture and a translocation core like bacterial Na+/H+ antiporters. Yet, the presence of distinct residues suggests that some CHXs differ from NHXs in pH sensing and electrogenicity. How H+ pumps, counter-ion fluxes, and cation/H+ antiporters are linked with signaling and membrane trafficking to remodel membranes and cell walls awaits further investigation.
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4.
Membrane Dynamics and Multiple Functions of Oil Bodies in Seeds and Leaves.
Shimada, TL, Hayashi, M, Hara-Nishimura, I
Plant physiology. 2018;(1):199-207
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Abstract
Oil bodies have multiple functions: oleosin-mediated freezing tolerance of seeds, direct interaction with glyoxysomes for lipid degradation in seedlings, and antifungal compound production in leaves.
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5.
Spatio-temporal dynamics of calcium electrotransfer during cell membrane permeabilization.
Guionet, A, Moosavi Nejad, S, Teissié, J, Sakugawa, T, Katsuki, S, Akiyama, H, Hosseini, H
Drug delivery and translational research. 2018;(5):1152-1161
Abstract
Pulsed electric fields (PEFs) are applied as physical stimuli for DNA/drug delivery, cancer therapy, gene transformation, and microorganism eradication. Meanwhile, calcium electrotransfer offers an interesting approach to treat cancer, as it induces cell death easier in malignant cells than in normal cells. Here, we study the spatial and temporal cellular responses to 10 μs duration PEFs; by observing real-time, the uptake of extracellular calcium through the cell membrane. The experimental setup consisted of an inverted fluorescence microscope equipped with a color high-speed framing camera and a specifically designed miniaturized pulsed power system. The setup allowed us to accurately observe the permeabilization of HeLa S3 cells during application of various levels of PEFs ranging from 0.27 to 1.80 kV/cm. The low electric field experiments confirmed the threshold value of transmembrane potential (TMP). The high electric field observations enabled us to retrieve the entire spatial variation of the permeabilization angle (θ). The temporal observations proved that after a minimal permeabilization of the cell membrane, the ionic diffusion was the prevailing mechanism of the delivery to the cell cytoplasm. The observations suggest 0.45 kV/cm and 100 pulses at 1 kHz as an optimal condition to achieve full calcium concentration in the cell cytoplasm. The results offer precise levels of electric fields to control release of the extracellular calcium to the cell cytoplasm for inducing minimally invasive cancer calcium electroporation, an interesting affordable method to treat cancer patients with minimum side effects.
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Impact of ticagrelor on P2Y1 and P2Y12 localization and on cholesterol levels in platelet plasma membrane.
Rabani, V, Montange, D, Meneveau, N, Davani, S
Platelets. 2018;(7):709-715
Abstract
Ticagrelor is an antiplatelet agent that inhibits platelet activation via P2Y12 antagonism. There are several studies showing that P2Y12 needs lipid rafts to be activated, but there are few data about how ticagrelor impacts lipid raft organization. Therefore, we aimed to investigate how ticagrelor could impact the distribution of cholesterol and consequently alter the organization of lipid rafts on platelet plasma membranes. We identified cholesterol-enriched raft fractions in platelet membranes by quantification of their cholesterol levels. Modifications in cholesterol and protein profiles (Flotillin 1, Flotillin 2, CD36, P2Y1, and P2Y12) were studied in platelets stimulated by ADP, treated by ticagrelor, or both. In ADP-stimulated and ticagrelor-treated groups, we found a decreased level of cholesterol in raft fractions of platelet plasma membrane compared to the control group. In addition, the peak of cholesterol in different experimental groups changed its localization on membrane fractions. In the control group, it was situated on fraction 2, while in ADP-stimulated platelets, it was located in fractions 3 to 5, and in fraction 4 in ticagrelor-treated group. The proteins studied also showed changes in their level of expression and localization in fractions of plasma membrane. Cholesterol levels of plasma membranes have a direct role in the organization of platelet membranes and could be modified by stimulation or drug treatment. Since ticagrelor and ADP both changed lipid composition and protein profile, investigating the lipid and protein composition of platelet membranes is of considerable importance as a focus for further research in anti-platelet management.
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Interfacial water molecules at biological membranes: Structural features and role for lateral proton diffusion.
Nguyen, TH, Zhang, C, Weichselbaum, E, Knyazev, DG, Pohl, P, Carloni, P
PloS one. 2018;(2):e0193454
Abstract
Proton transport at water/membrane interfaces plays a fundamental role for a myriad of bioenergetic processes. Here we have performed ab initio molecular dynamics simulations of proton transfer along two phosphatidylcholine bilayers. As found in previous theoretical studies, the excess proton is preferably located at the water/membrane interface. Further, our simulations indicate that it interacts not only with phosphate head groups, but also with water molecules at the interfaces. Interfacial water molecules turn out to be oriented relative to the lipid bilayers, consistently with experimental evidence. Hence, the specific water-proton interaction may help explain the proton mobility experimentally observed at the membrane interface.
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8.
Cell Penetrating Peptides: A Promising Tool for the Cellular Uptake of Macromolecular Drugs.
Zhu, P, Jin, L
Current protein & peptide science. 2018;(2):211-220
Abstract
The lipid bilayer of the plasma membrane is a selective impermeable barrier for the internalization of most macromolecules. Cell penetrating peptides (CPPs) could cross the plasma membrane barrier to deliver various molecules into cells and are considered as a promising tool to deliver macromolecular drugs. However, the exact cellular uptake mechanisms of CPPs are still ambiguous. It was reported that the exact cellular uptake pathway was determined by numerous factors such as the amino acid sequences (hydrophobicity and net charge), extracellular CPP concentration, cargoes' properties, cell type and the temperature. No matter what kind of mechanisms, the electrostatic interaction between the positive charged amino acids and the membrane with negatively charged glycosaminoglycans (GAGs), especially heparan sulphate proteoglycans (HSPGs), was supposed to be the first crucial step for CPPs uptake. The first recognition triggers cytoskeletal remodeling via activating Rho/Rac GTPases and kinase C, followed by the cell surface microdomains changing, ligand binding and cellular uptake. This review briefly discusses the classification, structure-activity relationships, cellular uptake mechanisms and biomedical applications of CPPs.
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Calcium transport across plant membranes: mechanisms and functions.
Demidchik, V, Shabala, S, Isayenkov, S, Cuin, TA, Pottosin, I
The New phytologist. 2018;(1):49-69
Abstract
Contents Summary 49 I. Introduction 49 II. Physiological and structural characteristics of plant Ca2+ -permeable ion channels 50 III. Ca2+ extrusion systems 61 IV. Concluding remarks 64 Acknowledgements 64 References 64 SUMMARY Calcium is an essential structural, metabolic and signalling element. The physiological functions of Ca2+ are enabled by its orchestrated transport across cell membranes, mediated by Ca2+ -permeable ion channels, Ca2+ -ATPases and Ca2+ /H+ exchangers. Bioinformatics analysis has not determined any Ca2+ -selective filters in plant ion channels, but electrophysiological tests do reveal Ca2+ conductances in plant membranes. The biophysical characteristics of plant Ca2+ conductances have been studied in detail and were recently complemented by molecular genetic approaches. Plant Ca2+ conductances are mediated by several families of ion channels, including cyclic nucleotide-gated channels (CNGCs), ionotropic glutamate receptors, two-pore channel 1 (TPC1), annexins and several types of mechanosensitive channels. Key Ca2+ -mediated reactions (e.g. sensing of temperature, gravity, touch and hormones, and cell elongation and guard cell closure) have now been associated with the activities of specific subunits from these families. Structural studies have demonstrated a unique selectivity filter in TPC1, which is passable for hydrated divalent cations. The hypothesis of a ROS-Ca2+ hub is discussed, linking Ca2+ transport to ROS generation. CNGC inactivation by cytosolic Ca2+ , leading to the termination of Ca2+ signals, is now mechanistically explained. The structure-function relationships of Ca2+ -ATPases and Ca2+ /H+ exchangers, and their regulation and physiological roles are analysed.
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Pro-necrotic Activity of Cationic Mastoparan Peptides in Human Glioblastoma Multiforme Cells Via Membranolytic Action.
da Silva, AMB, Silva-Gonçalves, LC, Oliveira, FA, Arcisio-Miranda, M
Molecular neurobiology. 2018;(7):5490-5504
Abstract
Glioblastoma multiforme is the most common and lethal malignant brain tumor. Because of its complexity and heterogeneity, this tumor has become resistant to conventional therapies and the available treatment produces multiple side effects. Here, using multiple experimental approaches, we demonstrate that three mastoparan peptides-Polybia-MP1, Mastoparan X, and HR1-from solitary wasp venom exhibit potent anticancer activity toward human glioblastoma multiforme cells. Importantly, the antiglioblastoma action of mastoparan peptides occurs by membranolytic activity, leading to necrosis. Our data also suggest a direct relation between mastoparan membranolytic potency and the presence of negatively charged phospholipids like phosphatidylserine. Collectively, these data may warrant additional studies for mastoparan peptides as new agents for the treatment of glioblastoma multiforme brain tumor.