Hydra actinoporin-like toxin 1

UniProtKB accession:  A0A8B7DWS6

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UniProtKB description:  Pore-forming protein that forms hydrophilic pores and causes cytolysis (PubMed:24768765, PubMed:31513812). Compared to equinatoxin-2 (AC P61914), it reveals lower cytolysis activity (5-12-fold difference, tested on erythrocytes), a larger pore size (probably 2-3 nm) and different affinity to membrane lipids (100-fold lower affinity to sphingomyelin) (PubMed:24768765). Binds to sulfatides (SFT) as well as to the two sphingolipids, lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) (PubMed:31513812). It seems to bind more strongly to LPA than to S1P and SFT (PubMed:31513812). Shows cytolytic activity on HeLa cells, with a different potency than its paralogs (from most potent to less potent: HALT-4>HALT-6~HALT-1>HALT-3>HALT-7>HALT-2) (PubMed:31513812). Pore formation is a multi-step process that involves specific recognition of membrane lipid by a protein aromatic residues rich region, firm binding to the membrane (mainly driven by hydrophobic interactions) accompanied by the transfer of the N-terminal region to the lipid-water interface and finally pore formation after oligomerization of monomers (By similarity) (PubMed:31513812). In vitro, binds to the folate receptor alpha (FOLR1), a GPI-anchored membrane protein that plays a major role in the uptake of folate/folic acid into cells via endocytosis, suggesting a possible involvement of this receptor in the mechanism of HALT-1-induced cell lysis (PubMed:28478056). In vivo, does not cause visible paralysis in larvae of the blowfly Sarcophaga faculata, the most common arthropod prey of Hydra (PubMed:24768765).