Comparative study of the cytoplasmic domain of band 3 from human and rabbit erythrocyte membranes

Changes in hematological, hemostatic and biochemical parameters induced experimentally in rabbits by Loxosceles gaucho spider venom

Human accidents caused by Loxosceles spiders may result in local dermal necrosis and, in some cases, severe systemic reactions - such as intravascular hemolysis, disseminated intravascular coagulation (DIC), renal failure and death. Since many aspects of envenomation by Loxosceles spiders remain unclear, we studied the hematological and hemostatic responses induced by the i.d. injection of 10 μg/kg Loxosceles gaucho venom in rabbits. For this purpose, total blood cell count, platelet function, coagulation tests and biochemical parameters were analysed at 3, 24, 48, 72 and 120 hours after venom administration. Thrombocytopenia and leukopenia were noted at 3 and 24 hours. Histopathological analysis of the skin lesion, performed at 24 hours after venom administration, showed a massive presence of leukocytes and platelets, hemorrhage and thrombus fornation at the injection site. At 72 and 120 hours, neutrophilic leukocytosis and thrombocytosis were observed. Platelet hyperaggregation was noticeable at 48 and 72 hours. Haptoglobin and fibrinogen levels were elevated early and remained in high levels over time. Significant increases in coagulation factors V, VII, VIII, IX, X and XI were noted at 120 hours. The results showed that neither intravascular hemolysis nor DIC occurred. However, the early onset of thrombocytopenia and leukopenia are important findings that may be related to dermal necrosis formation during loxoscelism.

The Type 1 secretion pathway - the hemolysin system and beyond

Type 1 secretion systems (T1SS) are wide-spread among Gram-negative bacteria. An important example is the secretion of the hemolytic toxin HlyA from uropathogenic strains. Secretion is achieved in a single step directly from the cytosol to the extracellular space. The translocation machinery is composed of three indispensable membrane proteins, two in the inner membrane, and the third in the outer membrane. The inner membrane proteins belong to the ABC transporter and membrane fusion protein families (MFPs), respectively, while the outer membrane component is a porin-like protein. Assembly of the three proteins is triggered by accumulation of the transport substrate (HlyA) in the cytoplasm, to form a continuous channel from the inner membrane, bridging the periplasm and finally to the exterior. Interestingly, the majority of substrates of T1SS contain all the information necessary for targeting the polypeptide to the translocation channel - a specific sequence at the extreme C-terminus. Here, we summarize our current knowledge of regulation, channel assembly, translocation of substrates, and in the case of the HlyA toxin, its interaction with host membranes. We try to provide a complete picture of structure function of the components of the translocation channel and their interaction with the substrate. Although we will place the emphasis on the paradigm of Type 1 secretion systems, the hemolysin A secretion machinery from E. coli, we also cover as completely as possible current knowledge of other examples of these fascinating translocation systems. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.

Mechanisms of hemolytic anemia during experimental methemoglobinemias

A complex study of the peripheral erythron component was performed during methemoglobinemias induced by single administration of sodium nitrate and phenylhydrazine in LD50. Administration of methemoglobin-forming agents to rats induced the development of hemolytic anemia. The pathogenesis of this disorder included significant long-term modifications of the erythrocyte membrane. The severity and duration of anemia syndrome depended on chemical structure of xenobiotics, blood methemoglobin level, and the duration of the acute period of methemoglobinemia.

The Calcium-binding C-terminal Domain of Escherichia coli α-Hemolysin Is a Major Determinant in the Surface-active Properties of the Protein

alpha-Hemolysin (HlyA) from Escherichia coli is a protein toxin (1024 amino acids) that targets eukaryotic cell membranes, causing loss of the permeability barrier. HlyA consists of two main regions, an N-terminal domain rich in amphipathic helices, and a C-terminal Ca(2+)-binding domain containing a Gly- and Asp-rich nonapeptide repeated in tandem 11-17 times. The latter is called the RTX domain and gives its name to the RTX protein family. It had been commonly assumed that membrane interaction occurred mainly if not exclusively through the amphipathic helix domain. However, we have cloned and expressed the C-terminal region of HlyA, containing the RTX domain plus a few stabilizing sequences, and found that it is a potent surface-active molecule. The isolated domain binds Ca(2+) with about the same affinity (apparent K(0.5) approximately 150 microM) as the parent protein HlyA, and Ca(2+) binding induces in turn a more compact folding with an increased proportion of beta-sheet structure. Both with and without Ca(2+) the C-terminal region of HlyA can interact with lipid monolayers spread at an air-water interface. However, the C-terminal domain by itself is devoid of membrane lytic properties. The present results can be interpreted in the light of our previous studies that involved in receptor binding a peptide in the C-terminal region of HlyA. We had also shown experimentally the distinction between reversible membrane adsorption and irreversible lytic insertion of the toxin. In this context, the present data allow us to propose that both major domains of HlyA are directly involved in membrane-toxin interaction, the nonapeptide repeat, calcium-binding RTX domain being responsible for the early stages of HlyA docking to the target membrane.

Anion permeability and erythrocyte swelling

Permeability of cell membranes to cations may increase as a result of membrane oxidation or in certain pathologies. We studied the effects of nonselective increases in cell membrane permeability to univalent cations on the volume of erythrocytes incubated in phosphate-buffered saline (PBS) using amphotericin B (5-10 mg/l suspension) or gramicidin D (10-100 microg/l suspension) as the membrane permeabilizing agents. Both antibiotics caused K+ to leak, Na+ to accumulate intracellularly, and cell volume to increase. The interval needed to reach the equilibrium between the intracellular and extracellular ion concentrations ranged from 30 min to several hours, depending on the antibiotic concentration. In spite of a rapid disappearance of cation transmembrane gradients, cell volume increased relatively slow. Even 24 h after the membrane permeability was changed, the volume of most erythrocytes did not increase to the lytic values (about 1.6 times the normal volume). The slow increase in erythrocyte volume was accounted for by slow changes in the transmembrane Cl- gradient. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), a specific inhibitor of anion transport, while producing no effect on the transmembrane Na+ and K+ fluxes induced by the antibiotics, significantly inhibited the decrease in the transmembrane Cl- gradient and the increase in erythrocyte volume. Analysis of these data by means of mathematical modeling showed that it failed to satisfactorily describe the experimental kinetics of erythrocyte swelling in response to increases in the membrane permeability to univalent cations if its permeability to Cl was set to be constant. The satisfactory description of this kinetics could be achieved by assuming that the membrane permeability to anions decreased with increasing erythrocyte volume. The results obtained demonstrate that transmembrane anion transport may be considered to be a component of the mechanism responsible for the erythrocyte volume stabilization, because a significant decrease in the swelling rate allows the erythrocytes with damaged membranes to activate a relatively slow (metabolic) mechanisms of cell volume stabilization and/or repair their damaged membranes.