Induction of human-fetal-membrane remodeling in-vitro by the alpha hemolysin of Escherichia coli.

Introduction: Almost 80% of urinary tract infections during pregnancy are caused by uropathogenic strains of Escherichia coli. Alpha-hemolysin, toxin secreted by them, has a fundamental role in this pathology development. Considering that urinary tract infections are related with premature rupture of fetal membranes, we proposed to evaluate the effects that alpha-hemolysin induces on human-fetal-membranes.

Alpha hemolysin of E. coli induces hemolysis of human erythrocytes independently of toxin interaction with membrane proteins.

Alpha hemolysin (HlyA) is a hemolytic and cytotoxic protein secreted by uropathogenic strains of E. coli. The role of glycophorins (GPs) as putative receptors for HlyA binding to red blood cells (RBCs) has been debated.

Biophysical Analysis to Assess the Interaction of CRAC and CARC Motif Peptides of Alpha Hemolysin of with Membranes.

Alpha hemolysin of (HlyA) is a pore-forming protein, which is a prototype of the "epeat in oins" (RTX) family. It was demonstrated that HlyA-cholesterol interaction facilitates the insertion of the toxin into membranes. Putative cholesterol-binding sites, called cholesterol recognition/amino acid consensus (CRAC), and CARC (analogous to CRAC but with the opposite orientation) were identified in the HlyA sequence.

Interactive Dynamics of Cell Volume and Cell Death in Human Erythrocytes Exposed to α-Hemolysin from .

α-hemolysin (HlyA) of binds irreversibly to human erythrocytes and induces cell swelling, ultimately leading to hemolysis. We characterized the mechanism involved in water transport induced by HlyA and analyzed how swelling and hemolysis might be coupled. Osmotic water permeability (P) was assessed by stopped-flow light scattering.

Anandamide Exerts a Differential Effect on Human Placenta Before and After the Onset of Labor.

The onset of labor involves the action of multiple factors and recent reports have postulated the endocannabinoid system as a new regulator of this process. Our objective was to study the role of anandamide, one of the main endocannabinoids, on the regulation of placental molecules that contribute to the onset of labor at term. Placental samples were obtained from patients with laboring vaginal deliveries and from non-laboring elective cesarean sections.

Role of Tryptophan Residues in the Toxicity and Photosensitized Inactivation of α-Hemolysin.

α-Hemolysin (HlyA) is an extracellular protein toxin secreted by uropathogenic strains of that inserts into membranes of eukaryotic cells. The main goal of this work was to investigate the involvement of tryptophan (W) residues in the hemolytic activity of HlyA. We investigated the hemolytic activity of six single-point mutant proteins, in which one of the four Ws was replaced by cysteine (C) or leucine (L).

Induction of erythrocyte microvesicles by Escherichia Coli Alpha hemolysin.

Alpha hemolysin (HlyA) is the major virulence factor of uropathogenic Escherichia coli (UPEC) strains. Once in circulation, a low concentration of the toxin induces an increase in intracellular calcium that activates calpains - which proteolyse cytoskeleton proteins - and also favours the exposure of phosphatidylserine (PS) in the outer leaflet of erythrocyte membranes. All these events are considered part of eryptosis, as well as the delivery of microvesicles (MVs).

Regulation of extracellular ATP of human erythrocytes treated with α-hemolysin. Effects of cell volume, morphology, rheology and hemolysis.

Alpha-hemolysin (HlyA) of uropathogenic strains of Escherichia coli irreversibly binds to human erythrocytes (RBCs) and triggers activation of ATP release and metabolic changes ultimately leading to hemolysis. We studied the regulation of extracellular ATP (ATPe) of RBCs exposed to HlyA. Luminometry was used to assess ATP release and ATPe hydrolysis, whereas changes in cell volume and morphology were determined by electrical impedance, ektacytometry and aggregometry.

ATPe Dynamics in Protozoan Parasites. Adapt or Perish.

In most animals, transient increases of extracellular ATP (ATPe) are used for physiological signaling or as a danger signal in pathological conditions. ATPe dynamics are controlled by ATP release from viable cells and cell lysis, ATPe degradation and interconversion by ecto-nucleotidases, and interaction of ATPe and byproducts with cell surface purinergic receptors and purine salvage mechanisms. Infection by protozoan parasites may alter at least one of the mechanisms controlling ATPe concentration.

Study of rabbit erythrocytes membrane solubilization by sucrose monomyristate using laurdan and phasor analysis.

The study of surfactant and bio membranes interaction is particularly complex due to the diversity in lipid composition and the presence of proteins in natural membranes. Even more difficult is the study of this interaction in vivo since cellular damage may complicate the interpretation of the results, therefore for most of the studies in this field either artificial or model systems are used. One of the model system most used to study biomembranes are erythrocytes due to their relatively simple structure (they lack nuclei and organelles having only the plasma membrane), their convenient experimental manipulation and availability.

Interaction of acylated and unacylated forms of E. coli alpha-hemolysin with lipid monolayers: a PM-IRRAS study.

Uropathogenic strains of Escherichia coli produce virulence factors, such as the protein toxin alpha-hemolysin (HlyA), that enable the bacteria to colonize the host and establish an infection. HlyA is synthetized as a protoxin (ProHlyA) that is transformed into the active form in the bacterial cytosol by the covalent linkage of two fatty-acyl moieties to the polypeptide chain before the secretion of HlyA into the extracellular medium. The aim of this work was to investigate the effect of the fatty acylation of HlyA on protein conformation and protein-membrane interactions.

Dynamic regulation of extracellular ATP in .

We studied the kinetics of extracellular ATP (ATPe) in and their outer membrane vesicles (OMVs) stimulated with amphipatic peptides melittin (MEL) and mastoparan 7 (MST7). Real-time luminometry was used to measure ATPe kinetics, ATP release, and ATPase activity. The latter was also determined by following [P]Pi released from [γ-P]ATP.

Induction of eryptosis by low concentrations of E. coli alpha-hemolysin.

Uropathogenic strains of Escherichia coli deliver the toxin alpha-hemolysin (HlyA) to optimize the host environment for the spread of infection. It was reported that at high concentrations, the toxin forms pores in eukaryotic membranes, leading to cell lysis, while lower concentrations have appeared to interfere with host-cell-signaling pathways causing cell death by apoptosis. Nevertheless, what is not clear is how often HlyA reaches levels that are high enough to lyse host target cells during the course of an infection.

N-nervonoylsphingomyelin (C24:1) prevents lateral heterogeneity in cholesterol-containing membranes.

This study was conducted to explore how the nature of the acyl chains of sphingomyelin (SM) influence its lateral distribution in the ternary lipid mixture SM/cholesterol/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), focusing on the importance of the hydrophobic part of the SM molecule for domain formation. Atomic force microscopy (AFM) measurements showed that the presence of a double bond in the 24:1 SM molecule in mixtures with cholesterol (CHO) or in pure bilayers led to a decrease in the molecular packing. Confocal microscopy and AFM showed, at the meso- and nanoscales respectively, that unlike 16:0 and 24:0 SM, 24:1 SM does not induce phase segregation in ternary lipid mixtures with DOPC and CHO.

Boundary region between coexisting lipid phases as initial binding sites for Escherichia coli alpha-hemolysin: a real-time study.

α-Hemolysin (HlyA) is a protein toxin, a member of the pore-forming Repeat in Toxin (RTX) family, secreted by some pathogenic strands of Escherichia coli. The mechanism of action of this toxin seems to involve three stages that ultimately lead to cell lysis: binding, insertion, and oligomerization of the toxin within the membrane. Since the influence of phase segregation on HlyA binding and insertion in lipid membranes is not clearly understood, we explored at the meso- and nanoscale-both in situ and in real-time-the interaction of HlyA with lipid monolayers and bilayers.

Novel evidence for the specific interaction between cholesterol and α-haemolysin of Escherichia coli.

Several toxins that act on animal cells present different, but specific, interactions with cholesterol or sphingomyelin. In the present study we demonstrate that HlyA (α-haemolysin) of Escherichia coli interacts directly with cholesterol. We have recently reported that HlyA became associated with detergent-resistant membranes enriched in cholesterol and sphingomyelin; moreover, toxin oligomerization, and hence haemolytic activity, diminishes in cholesterol-depleted erythrocytes.

Alpha hemolysin induces an increase of erythrocytes calcium: a FLIM 2-photon phasor analysis approach.

α-Hemolysin (HlyA) from Escherichia coli is considered as the prototype of a family of toxins called RTX (repeat in toxin), a group of proteins that share genetic and structural features. HlyA is an important virulence factor in E. coli extraintestinal infections, such as meningitis, septicemia and urinary infections.

Contribution of the C-terminal end of apolipoprotein AI to neutralization of lipopolysaccharide endotoxic effect.

It is well known that high density lipoprotein (HDL) binds bacterial lipopolysaccharide (LPS) and neutralizes its toxicity. The aim of this work was to study changes in the apolipoprotein (apo) AI structure after its interaction with LPS as well as to determine the protein domain involved in that interaction. The presented data indicate that LPS does not lead to major changes in the structure of apoAI, judging from Trp fluorescence spectra.

Fatty acids covalently bound to alpha-hemolysin of Escherichia coli are involved in the molten globule conformation: implication of disordered regions in binding promiscuity.

Alpha-hemolysin (HlyA) is a pore-forming toxin secreted by pathogenic strains of Escherichia coli. The toxin is synthesized as a protoxin, ProHlyA, which is matured in the cytosol to the active form by acylation at two internal lysines, K563 and K689 (HlyA). It is widely known that the presence of fatty acids is crucial for the hemolytic and cytotoxic effects of the toxin.

Paradoxical lipid dependence of pores formed by the Escherichia coli alpha-hemolysin in planar phospholipid bilayer membranes.

alpha-Hemolysin (HlyA) is an extracellular protein toxin (117 kDa) secreted by Escherichia coli that targets the plasma membranes of eukaryotic cells. We studied the interaction of this toxin with membranes using planar phospholipid bilayers. For all lipid mixtures tested, addition of nanomolar concentrations of toxin resulted in an increase of membrane conductance and a decrease in membrane stability.

Role of lipopolysaccharide on the structure and function of alpha-hemolysin from Escherichia coli.

alpha-Hemolysin (HlyA) is a protein toxin (107 kDa) secreted by some pathogenic strains of E. coli. Several studies suggested the relationship between HlyA and lipopolysaccharide (LPS).