oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
More Than a Pore: The Cellular Response to Cholesterol-Dependent Cytolysins  [PDF]
Sara K. B. Cassidy,Mary X. D. O'Riordan
Toxins , 2013, DOI: 10.3390/toxins5040618
Abstract: Targeted disruption of the plasma membrane is a ubiquitous form of attack used in all three domains of life. Many bacteria secrete pore-forming proteins during infection with broad implications for pathogenesis. The cholesterol-dependent cytolysins (CDC) are a family of pore-forming toxins expressed predominately by Gram-positive bacterial pathogens. The structure and assembly of some of these oligomeric toxins on the host membrane have been described, but how the targeted cell responds to intoxication by the CDCs is not as clearly understood. Many CDCs induce lysis of their target cell and can activate apoptotic cascades to promote cell death. However, the extent to which intoxication causes cell death is both CDC- and host cell-dependent, and at lower concentrations of toxin, survival of intoxicated host cells is well documented. Additionally, the effect of CDCs can be seen beyond the plasma membrane, and it is becoming increasingly clear that these toxins are potent regulators of signaling and immunity, beyond their role in intoxication. In this review, we discuss the cellular response to CDC intoxication with emphasis on the effects of pore formation on the host cell plasma membrane and subcellular organelles and whether subsequent cellular responses contribute to the survival of the affected cell.
The Cholesterol-Dependent Cytolysin Signature Motif: A Critical Element in the Allosteric Pathway that Couples Membrane Binding to Pore Assembly  [PDF]
Kelley J. Dowd,Rodney K. Tweten
PLOS Pathogens , 2012, DOI: 10.1371/journal.ppat.1002787
Abstract: The cholesterol-dependent cytolysins (CDCs) constitute a family of pore-forming toxins that contribute to the pathogenesis of a large number of Gram-positive bacterial pathogens.The most highly conserved region in the primary structure of the CDCs is the signature undecapeptide sequence (ECTGLAWEWWR). The CDC pore forming mechanism is highly sensitive to changes in its structure, yet its contribution to the molecular mechanism of the CDCs has remained enigmatic. Using a combination of fluorescence spectroscopic methods we provide evidence that shows the undecapeptide motif of the archetype CDC, perfringolysin O (PFO), is a key structural element in the allosteric coupling of the cholesterol-mediated membrane binding in domain 4 (D4) to distal structural changes in domain 3 (D3) that are required for the formation of the oligomeric pore complex. Loss of the undecapeptide function prevents all measurable D3 structural transitions, the intermolecular interaction of membrane bound monomers and the assembly of the oligomeric pore complex. We further show that this pathway does not exist in intermedilysin (ILY), a CDC that exhibits a divergent undecapeptide and that has evolved to use human CD59 rather than cholesterol as its receptor. These studies show for the first time that the undecapeptide of the cholesterol-binding CDCs forms a critical element of the allosteric pathway that controls the assembly of the pore complex.
The Cytolytic Activity of Vaginolysin Strictly Depends on Cholesterol and Is Potentiated by Human CD59  [PDF]
Milda Zilnyte,eslovas Venclovas,Aurelija Zvirbliene,Milda Pleckaityte
Toxins , 2015, DOI: 10.3390/toxins7010110
Abstract: Gardnerella vaginalis produces cytolysin vaginolysin (VLY), which has been suggested to be a contributor to bacterial vaginosis pathogenesis. VLY along with intermedilysin (ILY) from Streptococcus intermedius have been attributed to a group of cholesterol-dependent cytolysins (CDCs) whose pore-forming activity depends on human CD59 (hCD59). Here, we show that different types of cells lacking hCD59 are susceptible to VLY-mediated lysis, albeit to different extents. We analyze the effects of both hCD59 and cholesterol on VLY cytolytic activity. We show that VLY binds to cholesterol-rich membranes of non-human cells, while VLY with an impaired cholesterol recognition site retains binding to the hCD59-containing cells. We further demonstrate that cholesterol binding by VLY is sufficient to trigger the formation of oligomeric complexes on cholesterol rich-liposomes lacking hCD59. Thus, VLY may induce cell lysis following two alternative pathways. One requires only cholesterol and does not depend on hCD59. The second pathway involves hCD59 contribution similarly to ILY . Apparently, under physiological conditions VLY acts in the most effective way by accepting the assistance of hCD59.
Cholesterol-dependent hemolytic activity of Passiflora quadrangularis leaves
Yuldasheva, L.N.;Carvalho, E.B.;Catanho, M.-T.J.A.;Krasilnikov, O.V.;
Brazilian Journal of Medical and Biological Research , 2005, DOI: 10.1590/S0100-879X2005000700009
Abstract: plants used in traditional medicine are rich sources of hemolysins and cytolysins, which are potential bactericidal and anticancer drugs. the present study demonstrates for the first time the presence of a hemolysin in the leaves of passiflora quadrangularis l. this hemolysin is heat stable, resistant to trypsin treatment, has the capacity to froth, and acts very rapidly. the hemolysin activity is dose-dependent, with a slope greater than 1 in a double-logarithmic plot. polyethylene glycols of high molecular weight were able to reduce the rate of hemolysis, while liposomes containing cholesterol completely inhibited it. in contrast, liposomes containing phosphatidylcholine were ineffective. the passiflora hemolysin markedly increased the conductance of planar lipid bilayers containing cholesterol but was ineffective in cholesterol-free bilayers. successive extraction of the crude hemolysin with n-hexane, chloroform, ethyl acetate, and n-butanol resulted in a 10-fold purification, with the hemolytic activity being recovered in the n-butanol fraction. the data suggest that membrane cholesterol is the primary target for this hemolysin and that several hemolysin molecules form a large transmembrane water pore. the properties of the passiflora hemolysin, such as its frothing ability, positive color reaction with vanillin, selective extraction with n-butanol, hplc profile, cholesterol-dependent membrane susceptibility, formation of a stable complex with cholesterol, and rapid erythrocyte lysis kinetics indicate that it is probably a saponin.
Cholesterol-dependent hemolytic activity of Passiflora quadrangularis leaves  [cached]
Yuldasheva L.N.,Carvalho E.B.,Catanho M.-T.J.A.,Krasilnikov O.V.
Brazilian Journal of Medical and Biological Research , 2005,
Abstract: Plants used in traditional medicine are rich sources of hemolysins and cytolysins, which are potential bactericidal and anticancer drugs. The present study demonstrates for the first time the presence of a hemolysin in the leaves of Passiflora quadrangularis L. This hemolysin is heat stable, resistant to trypsin treatment, has the capacity to froth, and acts very rapidly. The hemolysin activity is dose-dependent, with a slope greater than 1 in a double-logarithmic plot. Polyethylene glycols of high molecular weight were able to reduce the rate of hemolysis, while liposomes containing cholesterol completely inhibited it. In contrast, liposomes containing phosphatidylcholine were ineffective. The Passiflora hemolysin markedly increased the conductance of planar lipid bilayers containing cholesterol but was ineffective in cholesterol-free bilayers. Successive extraction of the crude hemolysin with n-hexane, chloroform, ethyl acetate, and n-butanol resulted in a 10-fold purification, with the hemolytic activity being recovered in the n-butanol fraction. The data suggest that membrane cholesterol is the primary target for this hemolysin and that several hemolysin molecules form a large transmembrane water pore. The properties of the Passiflora hemolysin, such as its frothing ability, positive color reaction with vanillin, selective extraction with n-butanol, HPLC profile, cholesterol-dependent membrane susceptibility, formation of a stable complex with cholesterol, and rapid erythrocyte lysis kinetics indicate that it is probably a saponin.
Reconstitution of Cholesterol-Dependent Vaginolysin into Tethered Phospholipid Bilayers: Implications for Bioanalysis  [PDF]
Rima Budvytyte, Milda Pleckaityte, Aurelija Zvirbliene, David J. Vanderah, Gintaras Valincius
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0082536
Abstract: Functional reconstitution of the cholesterol-dependent cytolysin vaginolysin (VLY) from Gardnerella vaginalis into artificial tethered bilayer membranes (tBLMs) has been accomplished. The reconstitution of VLY was followed in real-time by electrochemical impedance spectroscopy (EIS). Changes of the EIS parameters of the tBLMs upon exposure to VLY solutions were consistent with the formation of water-filled pores in the membranes. It was found that reconstitution of VLY is a strictly cholesterol-dependent, irreversible process. At a constant cholesterol concentration reconstitution of VLY occurred in a concentration-dependent manner, thus allowing the monitoring of VLY concentration and activity in vitro and opening possibilities for tBLM utilization in bioanalysis. EIS methodology allowed us to detect VLY down to 0.5 nM (28 ng/mL) concentration. Inactivation of VLY by certain amino acid substitutions led to noticeably lesser tBLM damage. Pre-incubation of VLY with the neutralizing monoclonal antibody 9B4 inactivated the VLY membrane damage in a concentration-dependent manner, while the non-neutralizing antibody 21A5 exhibited no effect. These findings demonstrate the biological relevance of the interaction between VLY and the tBLM. The membrane-damaging interaction between VLY and tBLM was observed in the absence of the human CD59 receptor, known to strongly facilitate the hemolytic activity of VLY. Taken together, our study demonstrates the applicability of tBLMs as a bioanalytical platform for the detection of the activity of VLY and possibly other cholesterol-dependent cytolysins.
Changes in Astrocyte Shape Induced by Sublytic Concentrations of the Cholesterol-Dependent Cytolysin Pneumolysin Still Require Pore-Forming Capacity  [PDF]
Christina F?rtsch,Sabrina Hupp,Jiangtao Ma,Timothy J. Mitchell,Elke Maier,Roland Benz,Asparouh I. Iliev
Toxins , 2011, DOI: 10.3390/toxins3010043
Abstract: Streptococcus pneumoniae is a common pathogen that causes various infections, such as sepsis and meningitis. A major pathogenic factor of S. pneumoniae is the cholesterol-dependent cytolysin, pneumolysin. It produces cell lysis at high concentrations and apoptosis at lower concentrations. We have shown that sublytic amounts of pneumolysin induce small GTPase-dependent actin cytoskeleton reorganization and microtubule stabilization in human neuroblastoma cells that are manifested by cell retraction and changes in cell shape. In this study, we utilized a live imaging approach to analyze the role of pneumolysin’s pore-forming capacity in the actin-dependent cell shape changes in primary astrocytes. After the initial challenge with the wild-type toxin, a permeabilized cell population was rapidly established within 20–40 minutes. After the initial rapid permeabilization, the size of the permeabilized population remained unchanged and reached a plateau. Thus, we analyzed the non-permeabilized (non-lytic) population, which demonstrated retraction and shape changes that were inhibited by actin depolymerization. Despite the non-lytic nature of pneumolysin treatment, the toxin’s lytic capacity remained critical for the initiation of cell shape changes. The non-lytic pneumolysin mutants W433F-pneumolysin and delta6-pneumolysin, which bind the cell membrane with affinities similar to that of the wild-type toxin, were not able to induce shape changes. The initiation of cell shape changes and cell retraction by the wild-type toxin were independent of calcium and sodium influx and membrane depolarization, which are known to occur following cellular challenge and suggested to result from the ion channel-like properties of the pneumolysin pores. Excluding the major pore-related phenomena as the initiation mechanism of cell shape changes, the existence of a more complex relationship between the pore-forming capacity of pneumolysin and the actin cytoskeleton reorganization is suggested.
Mouse, but Not Human, ApoB-100 Lipoprotein Cholesterol Is a Potent Innate Inhibitor of Streptococcus pneumoniae Pneumolysin  [PDF]
Kristin R. Wade,Eileen M. Hotze,David E. Briles,Rodney K. Tweten
PLOS Pathogens , 2014, DOI: doi/10.1371/journal.ppat.1004353
Abstract: Streptococcus pneumoniae produces the pore-forming toxin pneumolysin (PLY), which is a member of the cholesterol-dependent cytolysin (CDC) family of toxins. The CDCs recognize and bind the 3β-hydroxyl group of cholesterol at the cell surface, which initiates membrane pore formation. The cholesterol transport lipoproteins, which carry cholesterol in their outer monolayer, are potential off-pathway binding targets for the CDCs and are present at significant levels in the serum and the interstitial spaces of cells. Herein we show that cholesterol carried specifically by the ApoB-100-containing lipoprotein particles (CH-ApoB-100) in the mouse, but not that carried by human or guinea pig particles, is a potent inhibitor of the PLY pore-forming mechanism. Cholesterol present in the outer monolayer of mouse ApoB-100 particles is recognized and bound by PLY, which stimulates premature assembly of the PLY oligomeric complex thereby inactivating PLY. These studies further suggest that the vast difference in the inhibitory capacity of mouse CH-ApoB-100 and that of the human and the guinea pig is due to differences in the presentation of cholesterol in the outer monolayer of their ApoB-100 particles. Therefore mouse CH-ApoB-100 represents a significant innate CDC inhibitor that is absent in humans, which may underestimate the contribution of CDCs to human disease when utilizing mouse models of disease.
PKC-Dependent Phosphorylation of eNOS at T495 Regulates eNOS Coupling and Endothelial Barrier Function in Response to G+ -Toxins  [PDF]
Feng Chen, Sanjiv Kumar, Yanfang Yu, Saurabh Aggarwal, Christine Gross, Yusi Wang, Trinad Chakraborty, Alexander D. Verin, John D. Catravas, Rudolf Lucas, Stephen M. Black, David J. R. Fulton
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0099823
Abstract: Gram positive (G+) infections make up ~50% of all acute lung injury cases which are characterized by extensive permeability edema secondary to disruption of endothelial cell (EC) barrier integrity. A primary cause of increased permeability are cholesterol-dependent cytolysins (CDCs) of G+-bacteria, such as pneumolysin (PLY) and listeriolysin-O (LLO) which create plasma membrane pores, promoting Ca2+-influx and activation of PKCα. In human lung microvascular endothelial cells (HLMVEC), pretreatment with the nitric oxide synthase (NOS) inhibitor, ETU reduced the ability of LLO to increase microvascular cell permeability suggesting an endothelial nitric oxide synthase (eNOS)-dependent mechanism. LLO stimulated superoxide production from HLMVEC and this was prevented by silencing PKCα or NOS inhibition suggesting a link between these pathways. Both LLO and PLY stimulated eNOS T495 phosphorylation in a PKC-dependent manner. Expression of a phosphomimetic T495D eNOS (human isoform) resulted in increased superoxide and diminished nitric oxide (NO) production. Transduction of HLMVEC with an active form of PKCα resulted in the robust phosphorylation of T495 and increased peroxynitrite production, indicative of eNOS uncoupling. To determine the mechanisms underlying eNOS uncoupling, HLMVEC were stimulated with LLO and the amount of hsp90 and caveolin-1 bound to eNOS determined. LLO stimulated the dissociation of hsp90, and in particular, caveolin-1 from eNOS. Both hsp90 and caveolin-1 have been shown to influence eNOS uncoupling and a peptide mimicking the scaffolding domain of caveolin-1 blocked the ability of PKCα to stimulate eNOS-derived superoxide. Collectively, these results suggest that the G+ pore-forming toxins promote increased EC permeability via activation of PKCα, phosphorylation of eNOS-T495, loss of hsp90 and caveolin-1 binding which collectively promote eNOS uncoupling and the production of barrier disruptive superoxide.
Pore formation in fluctuating membranes  [PDF]
Oded Farago,Christian D. Santangelo
Physics , 2004, DOI: 10.1063/1.1835952
Abstract: We study the nucleation of a single pore in a fluctuating lipid membrane, specifically taking into account the membrane fluctuations, as well as the shape fluctuations of the pore. For large enough pores, the nucleation free energy is well-described by shifts in the effective membrane surface tension and the pore line tension. Using our framework, we derive the stability criteria for the various pore formation regimes. In addition to the well-known large-tension regime from the classical nucleation theory of pores, we also find a low-tension regime in which the effective line and surface tensions can change sign from their bare values. The latter scenario takes place at sufficiently high temperatures, where the opening of a stable pore of finite size is entropically favorable.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.