RESUMEN
Cnidarians rely on their nematocysts and the venom injected through these unique weaponry systems to catch prey and protect themselves from predators. The development and physiology of the nematocysts of Hydra magnipapillata, a classic model organism, have been intensively studied, yet the composition and biochemical activity of their venom components are mostly unknown. Here, we show that hydra actinoporin-like toxins (HALTs), which have previously been associated with Hydra nematocysts, belong to a multigene family comprising six genes, which have diverged from a single common ancestor. All six genes are expressed in a population of Hydra magnipapillata. When expressed recombinantly, HALT-1 (Δ-HYTX-Hma1a), an actinoporin-like protein found in the stenoteles (the main penetrating nematocysts used in prey capture), reveals hemolytic activity, albeit about two-thirds lower than that of the anemone actinoporin equinatoxin II (EqTII, Δ-AITX-Aeq1a). HALT-1 also differs from EqTII in the size of its pores, and likely does not utilize sphingomyelin as a membrane receptor. We describe features of the HALT-1 sequence which may contribute to this difference in activity, and speculate on the role of this unusual family of pore-forming toxins in the ecology of Hydra.
Asunto(s)
Proteínas Hemolisinas/toxicidad , Hydra/química , Toxinas Marinas/toxicidad , Familia de Multigenes , Secuencia de Aminoácidos , Animales , Cartilla de ADN , Proteínas Hemolisinas/genética , Proteínas Hemolisinas/aislamiento & purificación , Hemólisis , Toxinas Marinas/genética , Toxinas Marinas/aislamiento & purificación , Datos de Secuencia Molecular , Filogenia , Reacción en Cadena de la Polimerasa , Homología de Secuencia de AminoácidoRESUMEN
A novel biologically active peptide (metamorphosin A, MMA, pEQPGLW.NH2) has recently been described. It was isolated from Anthopleura elegantissima and triggers metamorphosis in Hydractinia echinata. Antibodies directed against the C-terminal part of the molecule immunohistochemically stain neurosensory cells and processes in the anterior part of larvae of H. echinata. We assume that in metamorphosis MMA (or a closely related LW-amide) is an internal signal transmitted from the anterior to the posterior body parts. Immunoreactivity is also found in ectodermal nerve processes - but not cell bodies - in the tentacles and in the basal disk of the foot of Hydra magnipapillata. This is, to our knowledge, the first report of LW-amide(s) as (a) neuropeptide(s).
RESUMEN
A wealth of information has suggested the involvement of protein kinase C (PKC) in metamorphosis of Hydractinia echinata and in pattern formation of Hydra magnipapillata. We have identified a Ca2+- and phospholipid-dependent kinase activity in extracts of both species. The enzyme was characterized as being similar to mammalian PKC by ion exchange chromatography. Gel filtration experiments revealed a molecular weight of about 70 kD. In phosphorylation assays of endogenous Hydractinia proteins, a protein with a molecular weight of 22.5 kD was found to be phoshorylated upon addition of phosphatidylserine. Bacterial induction of metamorphosis of Hydractinia echinata caused an increase in endogenous diacylglycerol, the physiological activator of PKC, suggesting that the bacterial inducer acts by activating receptor-regulated phospholipid metabolism. Exogenous diacylglycerol leads to membrane translocation of PKC, indicative of an activation. On the basis of our results and those of Freeman and Ridgway (1990) a model for the biochemical events during metamorphosis is presented.