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Anthrax is a toxin-mediated disease, the lethal effects of which are initiated by the binding of protective antigen ( PA) with one of three reported cell surface toxin receptors ( ANTXR). Receptor binding has been shown to influence host susceptibility to the toxins. Despite this crucial role for ANTXR in the outcome of disease, and the reported immunomodulatory consequence of the anthrax toxins during infection, little is known about ANTXR expression on human leucocytes. We characterized the expression levels of ANTXR1 ( TEM8) on human leucocytes using flow cytometry. In order to assess the effect of prior toxin exposure on ANTXR1 expression levels, leucocytes from individuals with no known exposure, those exposed to toxin through vaccination and convalescent individuals were analysed. Donors could be defined as either 'low' or 'high' expressers based on the percentage of ANTXR1-positive monocytes detected. Previous exposure to toxins appears to modulate ANTXR1 expression, exposure through active infection being associated with lower receptor expression. A significant correlation between low receptor expression and high anthrax toxin-specific interferon ( IFN)-γ responses was observed in previously infected individuals. We propose that there is an attenuation of ANTXR1 expression post-infection which may be a protective mechanism that has evolved to prevent reinfection. [ABSTRACT FROM AUTHOR]

Soluble receptor decoy inhibitors, including receptor-immunogloubulin (Ig) fusion proteins, have shown promise as candidate anthrax toxin therapeutics. These agents act by binding to the receptor-interaction site on the protective antigen (PA) toxin subunit, thereby blocking toxin binding to cell surface receptors. Here we have made the surprising observation that co-administration of receptor decoy-Ig fusion proteins significantly delayed, but did not protect, rats challenged with anthrax lethal toxin. The delayed toxicity was associated with the in vivo assembly of a long-lived complex comprised of anthrax lethal toxin and the receptor decoy-Ig inhibitor. Intoxication in this system presumably results from the slow dissociation of the toxin complex from the inhibitor following their prolonged circulation. We conclude that while receptor decoy-Ig proteins represent promising candidates for the early treatment of B. anthracis infection, they may not be suitable for therapeutic use at later stages when fatal levels of toxin have already accumulated in the bloodstream. [ABSTRACT FROM AUTHOR]

Toll-like receptors (TLRs) are pattern recognition receptors that recognize conserved molecular patterns expressed by pathogens. Pneumolysin, an intracellular toxin found in all Streptococcus pneumoniae clinical isolates, is an important virulence factor of the pneumococcus that is recognized by TLR4. Although TLR2 is considered the most important receptor for Gram-positive bacteria, our laboratory previously could not demonstrate a decisive role for TLR2 in host defence against pneumonia caused by a serotype 3 S. pneumoniae. Here we tested the hypothesis that in the absence of TLR2, S. pneumoniae can still be sensed by the immune system through an interaction between pneumolysin and TLR4. C57BL/6 wild-type (WT) and TLR2 knockout (KO) mice were intranasally infected with either WT S. pneumoniae D39 (serotype 2) or the isogenic pneumolysin-deficient S. pneumoniae strain D39 PLN. TLR2 did not contribute to antibacterial defence against WT S. pneumoniae D39. In contrast, pneumolysin-deficient S. pneumoniae only grew in lungs of TLR2 KO mice. TLR2 KO mice displayed a strongly reduced early inflammatory response in their lungs during pneumonia caused by both pneumolysin-producing and pneumolysin-deficient pneumococci. These data suggest that pneumolysin-induced TLR4 signalling can compensate for TLR2 deficiency during respiratory tract infection with S. pneumoniae. [ABSTRACT FROM AUTHOR]

Abstract: We used quantitative real-time RT-PCR to not only investigate the mRNA levels of anthrax toxin receptor 1 (ANTXR1) and 2 (ANTXR2) in the murine J774A.1 macrophage cells and different tissues of mice, but also evaluate the effect of anthrax edema toxin and Bacillus anthracis Sterne spores on the expression of mRNA of these receptors. The mRNA transcripts of both receptors were detected in J774A.1 cells and mouse tissues such as the lung, heart, kidney, spleen, stomach, jejunum, brain, skeleton muscle, and skin. The ANTXR2 mRNA level was significantly higher than that of ANTXR1 in J774A.1 cells and all tissues examined. The mRNA expression of both receptors in the lung was the highest among the tissues evaluated. Interestingly, the mRNA expression of both receptors in J774A.1 cells was upregulated by edema toxin. In addition, ANTXR mRNA expression in the lung was downregulated after subcutaneous inoculation of B. anthracis Sterne spores as well as after intranasal administration of anthrax toxin-based vaccine BioThrax™. These results suggest that anthrax edema toxin and B. anthracis Sterne spore are involved in the ANTXR mRNA regulation in host cells. [Copyright &y& Elsevier]

Mutations in capillary morphogenesis gene 2 ( CMG2), one of the two closely related proteins that act as anthrax toxin receptors, cause two rare human autosomal recessive conditions, juvenile hyaline fibromatosis (JHF) and infantile systemic hyalinosis (ISH). Here we demonstrate that CMG2 proteins with certain JHF- and ISH-associated single amino acid substitutions in their von Willebrand factor A domain or transmembrane region do not function as anthrax toxin receptors. However, an ISH-associated CMG2 variant having a truncated cytosolic domain does still function as an anthrax receptor, and in fact makes cells hyper-sensitive to toxin, distinguishing the roles of CMG2 in physiology and anthrax pathology. Site-specific mutagenesis was used to characterize the role that domain 2 of the anthrax toxin protective antigen (PA) plays in interaction with CMG2, focusing on the interaction between the PA 2β3−2β4 loop and a pocket (Glu-122 pocket) adjacent to the metal ion-dependent adhesion site in CMG2. Substitutions that disrupted the salt bridge between PA Arg-344 and CMG2 Glu-122 decreased the affinity of PA to CMG2 three- to fourfold. Furthermore, mutation of CMG2 Tyr-119 (within the Glu-122 pocket) to His lowered the pH threshold for PA prepore-to-pore conversion in the endocytic pathway. [ABSTRACT FROM AUTHOR]

We report the definition and characterization of a conotoxin subfamily, designated the short αA-conotoxins (αAs) and demonstrate that all of these share the unique property of selectively antagonizing the fetal subtype of the mammalian neuromuscular nicotinic acetylcholine receptor (nAChR). We have characterized newly identified αAs-conotoxins from Conus pergrandis and have conducted a more detailed characterization of αA-conotoxins previously reported from additional Conus species. Among the results, the characterization of the short αA-conotoxins revealed diverse kinetics of a block of the fetal muscle nAChR, particularly in dissociation rates. The structure-function relationships of native αAs-conotoxins and some analogues revealed a single amino acid locus (alternatively either His or Pro in native peptides) that is a critical determinant of the dissociation kinetics. The unprecedented binding selectivity for the fetal muscle nAChR, coupled with the kinetic diversity, should make αAs-conotoxins useful ligands for a diverse set of studies. The rapidly reversible peptides may be most suitable for electrophysiological studies, while the relatively irreversible peptides should be most useful for binding and localization studies. [ABSTRACT FROM AUTHOR]

The specific role of cadherin receptors in cytotoxicity involving Cry toxins of Bacillus thuringiensis and their interactions with cell membrane has not been defined. To elucidate the involvement of toxin-membrane and toxin-receptor interactions in cytotoxicity, we established a cell-based system utilizing High Five insect cells stably expressing BT-R1, the cadherin receptor for Cry1Ab toxin. Cry1Ab toxin is incorporated into cell membrane in both oligomeric and monomeric form. Monomeric toxin binds specifically to BT-R1 whereas incorporation of oligomeric toxin is nonspecific and lipid dependent. Toxin oligomers in the cell membrane do not produce lytic pores and do not kill insect cells. Rather, cell death correlates with binding of the Cry1Ab toxin monomer to BT-R1, which apparently activates a Mg2+-dependent cellular signaling pathway.Cell Death and Differentiation (2005) 12, 1407–1416. doi:10.1038/sj.cdd.4401675; published online 27 May 2005 [ABSTRACT FROM AUTHOR]

After binding to cellular receptors and proteolytic activation, the protective antigen component of anthrax toxin forms a heptameric prepore. The prepore later undergoes pH-dependent conversion to a pore, mediating translocation of the edema and lethal factors to the cytosol. We describe structures of the prepore (3.6 Å) and a prepore:receptor complex (4.3 Å) that reveal the location of pore-forming loops and an unexpected interaction of the receptor with the pore-forming domain. Lower pH is required for prepore-to-pore conversion in the presence of the receptor, indicating that this interaction regulates pH-dependent pore formation. We present an example of a receptor negatively regulating pH-dependent membrane insertion. [ABSTRACT FROM AUTHOR]

Studies the receptor-mediated actions of α-Latrotoxin (LTX) using the toxin mutant LTX[supN4C]. Properties of LTX[supN4C]-induced spontaneous release; Dual mode of action of LTX[supWT]; Presynaptic receptors binded by LTX.

Reports on the infection of Saccharomyces cerevisiae K1 killer strains by the M1 double-stranded RNA virus encoding a secret protein toxin that kills sensitive cells by disrupting cytoplasmic membrane function. Mediation of toxin binding to spheroplasts by Krep1, a cell wall protein initially attached to the plasma membrane by its C-terminal GPI anchor.

Presents information on a study which examined the molecular components and physical location of the Hanatoxin receptors on the voltage-gated potassium channels in the cell membrane. Experimental procedure; Results and discussion; Conclusion.