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 org anisms for biomonitoring programmes. Previously it was reported that the ma rine sponge Suberites domuncula reacts to cadmium, both under controlled la boratory conditions and in the field with an increased expression of the he at-shock protein 70 and with DNA damage. In this study it is shown that thi s sponge contains a cadmium-binding protein with a M-r of 24 000. Cloning s tudies detected a gene in S. domuncula, termed SDMTL, which encodes a putat ive polypeptide, MTL_SUBDO, that shares high sequence similarity with metal lothioneins (MTs) from Metazoa. The open reading frame displays a polypepti de 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 m etazoan 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), demons trated a correlation between the environmental load with cadmium (accumulat ion of this metal in the animals) and the expression of the gene encoding t he 'detoxifying' cadmium-binding protein, MTL, in the test animals. These d ata suggest that the discovered MTL gene from S. domuncula is a sensitive i ndicator for environmental, bioavailable cadmium.