title: A hydra with many heads: protein and polypeptide toxins from hydra and their biological roles.
abstract: Hydra have been classical model organisms for over 250 years, yet little is known about the toxins they produce, and how they utilize these toxins to catch prey, protect themselves from predators and fulfill other biological roles necessary for survival. Unlike typical venomous organisms the hydra allomonal system is complex and "holistic", produced by various stinging cells (in the hunting tentacles and body ectoderm) as well as by non-nematocystic tissue. Toxic proteins also fulfill novel, non-allomonal roles in hydra. This review described the toxins produced by hydra within the context of their biology and natural history. Hydra nematocyst venom contains a high-molecular weight (>100 kDa) hemolytic and paralytic protein and a protein of approximately 30 kDa which induces a long-lasting flaccid paralysis. No low-molecular weight toxicity is observed, suggesting the lack of "classical" 4-7 kDa neurotoxins. The occurrence of a potent phospholipase activity in the venom is supported by the detection of several venom-like phospholipase A2 genes expressed by hydra. Hydra also produce toxins which are not part of the nematocyst venom. In the green hydra, Hydralysins, a novel family of Pore-Forming Proteins, are secreted into the gastrovascular cavity during feeding, probably helping in disintegration of the prey. Other putative non-nematocystic "toxins" may be involved in immunity, development or regulation of behavior. As the first venomous organism for which modern molecular tools are available, hydra provide a useful model to answer many outstanding questions on the way venomous organisms utilize their toxins to survive.
authors.affiliation: Department of Cell and Animal Biology, Silberman Institute of Life Sciences, Hebrew University, Jerusalem 91904, Israel. dsher@mit.edu
authors.forename: Daniel
authors.initials: D
authors.lastname: Sher
authors.forename: Eliahu
authors.initials: E
authors.lastname: Zlotkin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003064:Cnidarian Venoms / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D006829:Hydra / Q000737:chemistry / Q000166:cytology / Q000502:physiology; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D010455:Peptides / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D052899:Pore Forming Cytotoxic Proteins / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D011506:Proteins / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity
chemical_list: D003064:Cnidarian Venoms; D009498:Neurotoxins; D010455:Peptides; D052899:Pore Forming Cytotoxic Proteins; D011506:Proteins