A TOXIN HOMOLOGY DOMAIN IN AN ASTACIN-LIKE METALLOPROTEINASE OF THE JELLYFISH PODOCORYNE CARNEA WITH A DUAL ROLE IN DIGESTION AND DEVELOPMENT

Metalloproteinases of the astacin family such as tolloid play major ro les in animal morphogenesis. Cnidarians are thought to be evolutionary simple organisms and, therefore, a metalloproteinase from the marine hydrozoan Podocoryne carnea was analysed to evaluate the role of this conserved gene familiy at the base of animal evolution. Surprisingly, the proteinase domain of Podocornyne PMP1 is more similar to human mep rin than to HMP1 from another hydrozoan, the freshwater polyp Hydra vu lgaris. However, PMP1 and HMP1 both contain a small C-terminal domain with six cysteines that distinguishes them from other astacin-like mol ecules. Similar domains have been described only recently from sea ane mone toxins specific for potassium channels. This toxin homology (Tox1 ) domain is clearly distinct from epidermal growth factor (EGF)-like d omains or other cysteine-rich modules and terminates with the characte ristic pattern CXXXCXXC with three out of six cysteines in the last ei ght residues of the protein. PMP1 is transiently expressed at various sites of morphogenetic activity during medusa bud development. In the adult medusa, however, expression is concentrated to the manubrium, th e feeding organ, where the PMP1 gene is highly induced upon feeding. T hese disparate expression patterns suggest a dual role of PMP1 compara ble to tolloid in development and, like astacin in the crayfish, also for food digestion. The Tox1 domain of PMP1 could serve as a toxin to keep the pray paralysed after ingestion, but as a sequence module such Tox1 domains with six cysteines are neither restricted to cnidarians nor to toxins.