A multigene family of Heteractis magnificalysins (HMgs)

Sea anemones are passive predators. They use their specialized stinging cells (nematocysts) to immobilize any prey that blunders into them. A cnida fires, everting a tubule which delivers toxins that may stick to a prey. These toxins include neurotoxins, cytotoxins, cardiotoxins and haemolysins. Heteractis magnificalysins (HMgs) belong to a family of cytolysins from the sea anemone Heteractis magnifica. HMgs are 19.5 kDa basic proteins of 177 amino acids with pI values ranging from 8 to 10. From 52 cloned HMg gene sequences, we showed that HMgs are encoded by a multigene family whose members are highly homologous to each other. HMg genes are intronless, and may have arisen by gene duplication, gene conversion or mutation. By modifying the extraction procedure, we purified more natural HMg proteins from H. magnifica, thus demonstrating that H. magnifica are naturally competent to produce a large number of HMg cytolysins. Native and recombinant HMg proteins differed from each other in their amino acid sequences and biological activities. In each H. magnifica, many cytolysin isoforms are produced. H. magnifica appeared to have evolved a survival mechanism whereby a large number of cytolysins of different biological properties are produced for defense and offence.