Purification, cDNA cloning and expression of a cadmium-inducible cysteine-rich metallothionein-like protein from the marine sponge Suberites domuncula

During the last few years sponges have been proven to be suitable model organisms for biomonitoring programmes. Previously it was reported that the marine sponge Suberites domuncula reacts to cadmium, both under controlled laboratory conditions and in the field with an increased expression of the heat-shock protein 70 and with DNA damage. In this study it is shown that this sponge contains a cadmium-binding protein with a M-r of 24 000. Cloning studies detected a gene in S. domuncula, termed SDMTL, which encodes a putative polypeptide, MTL_SUBDO, that shares high sequence similarity with metallothioneins (MTs) from Metazoa. The open reading frame displays a polypeptide with a calculated size of M-r of 17 103. Phylogenetic analysis revealed that the sponge molecule, termed MT-like (MTL) protein, is related to the metazoan MTs. Under laboratory conditions, no expression of the SDMTL can be detected. After 1 d, incubation of the sponges with cadmium (200 mu g l(-1)) already revealed a dramatic upregulation of the MTL gene in S. domuncula. Subsequent studies in the field, the area around Rovinj (Croatia), demonstrated a correlation between the environmental load with cadmium (accumulation of this metal in the animals) and the expression of the gene encoding the 'detoxifying' cadmium-binding protein, MTL, in the test animals. These data suggest that the discovered MTL gene from S. domuncula is a sensitive indicator for environmental, bioavailable cadmium.