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

Abstract

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 ϳ1.2 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.

Solubilization, Activation, and Insecticidal Activity ofBacillus thuringiensisSerovar thompsoni HD542 Crystal Proteins

“…Although these proteins have low overall sequence similarity, they share conserved sequence motifs consisting of an amphipathic loop region flanked by two Ser/Thr-rich regions (Fig. 6), with each other as well as with a large and diverse group of protein toxins from a variety of organisms (23). The threedimensional structures of aerolysin (18), epsilon toxin (6), and Laetiporus sulphureus (a mushroom) hemolytic pore-forming lectin (23) suggest that these motifs represent beta-sheets and an amphipathic loop region, which in alpha-toxin has been shown to insert into the target membrane (15).…”

“…6), with each other as well as with a large and diverse group of protein toxins from a variety of organisms (23). The threedimensional structures of aerolysin (18), epsilon toxin (6), and Laetiporus sulphureus (a mushroom) hemolytic pore-forming lectin (23) suggest that these motifs represent beta-sheets and an amphipathic loop region, which in alpha-toxin has been shown to insert into the target membrane (15). These structural analogies suggest that Cry15 and the other toxins dis- In this paper, we have investigated some of the biochemical and insecticidal properties of Cry15Aa and the 40-kDa protein, encoded by the cry15Aa operon.…”

How to use Hydra as a model system to teach biology in the classroom

“…a functional barrier to the environment); the inner epithelium (endoderm) contains myoepithelial cells that act as digestive cells, phagocytosing nutrients with the help of the gland cells that secrete proteases (Lentz, 1966). In green Hydra (that contain intracellular Chlorella-like algae) specific Hydra lysins belonging to a novel family of Pore-Forming Proteins are secreted into the gastrovascular cavity probably aiding in the digestion of prey (Sher et al, 2005).…”

“…a functional barrier to the environment); the inner epithelium (endoderm) contains myoepithelial cells that act as digestive cells, phagocytosing nutrients with the help of the gland cells that secrete proteases (Lentz, 1966). In green Hydra (that contain intracellular Chlorella-like algae) specific Hydra lysins belonging to a novel family of Pore-Forming Proteins are secreted into the gastrovascular cavity probably aiding in the digestion of prey (Sher et al, 2005).Both epithelial layers contain interstitial cell derivatives; indeed interstitial stem cells (that are exclusively found in the ectoderm) differentiate into nerve cells and nematocytes (mechano-sensory cells characteristic of Cnidaria), but also into gland cells that migrate towards the endoderm as well as germ cells when the animal follow the sexual cycle (Bode, 1996b). Nerve cells are found in both layers.…”

What Hydra can teach us about chemical ecology how a simple, soft organism survives in a hostile aqueous environment

“…Hydra produce a multitude of potentially bioactive compounds, including hemolysins likely involved in digestion (Sher et al, 2008, Sher et al, 2005a, Zhang et al, 2003, other potential pore-forming proteins involved in development and immunity (Amimoto et al, 2006, Miller et al, 2007, Sher and Zlotkin, 2009), neuropeptides and signaling peptides (Bosch and Fujisawa, 2001, Bottger et al, 2006, Takahashi et al, 1997, see in this issue (Fujisawa and Kayakawa, 2012;Pierobon, 2012) and several antimicrobial peptides (Augustin et al, 2009, Fraune et al, 2010. These proteins and peptides are produced by different body regions or cells, and several are secreted either into the gastrovascular cavity (Sher et al, 2008), into the developing oocyte or onto the ectodermal surface (Fraune et al, 2010).…”