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J. Biol. Chem., Vol. 280, Issue 24, 22847-22855, June 17, 2005

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Hydralysins, a New Category of -Pore-forming Toxins in Cnidaria^*

Daniel Sher, Yelena Fishman, Mingliang Zhang, Mario Lebendiker, Ariel Gaathon¶, José-Miguel Mancheño||, and Eliahu Zlotkin**

From the Department of Cell and Animal Biology and Wolfson Center for Applied Structural Biology, Silberman Institute of Life Sciences, Hebrew University, Jerusalem 91904, Israel, ^¶Blettereman Laboratory for Macromolecules, Hebrew University Medical School, Jerusalem 91120, Israel, and ^||Instituto de Quimica-Fisica Rocasolano, Consejo Superior de Investigaciones Científicas, Departamento de Cristalografia, Serrano 119, E-28006 Madrid, Spain

Cnidaria are venomous animals that produce diverse protein and polypeptide toxins, stored and delivered into the prey through the stinging cells, the nematocytes. These include pore-forming cytolytic toxins such as well studied actinoporins. In this work, we have shown that the non-nematocystic paralytic toxins, hydralysins, from the green hydra Chlorohydra viridissima comprise a highly diverse group of -pore-forming proteins, distinct from other cnidarian toxins but similar in activity and structure to bacterial and fungal toxins. Functional characterization of hydralysins reveals that as soluble monomers they are rich in -structure, as revealed by far UV circular dichroism and computational analysis. Hydralysins bind erythrocyte membranes and form discrete pores with an internal diameter of 1.2 nm. The cytolytic effect of hydralysin is cell type-selective, suggesting a specific receptor that is not a phospholipid or carbohydrate. Multiple sequence alignment reveals that hydralysins share a set of conserved sequence motifs with known pore-forming toxins such as aerolysin, -toxin, -toxin, and LSL and that these sequence motifs are found in and around the poreforming domains of the toxins. The importance of these sequence motifs is revealed by the cloning, expression, and mutagenesis of three hydralysin isoforms that strongly differ in their hemolytic and paralytic activities. The correlation between the paralytic and cytolytic activities of hydralysin suggests that both are a consequence of receptor-mediated pore formation. Hydralysins and their homologues exemplify the wide distribution of -pore formers in biology and provide a useful model for the study of their molecular mode of action.

Received for publication, March 24, 2005

^* This work was supported by Grant 476/01 from the Israel Science Foundation, founded by the Israel Academy of Sciences and Humanities. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. The nucleotide sequence(s) reported in this paper has been submitted to the DDBJ/GenBank^TM/EBI Data Bank with accession number(s) AY655142, AY967765, and AY967764.

The on-line version of this article (available at http://www.jbc.org) contains a supplemental figure.

^** To whom correspondence should be addressed. Tel.: 972-2-6585933; Fax: 972-2-5617918; E-mail: zlotkin{at}vms.huji.ac.il.

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