Primary structure of a cadmium-induced metallothionein from the insect Orchesella cincta (Collembola)

The induction of metallothionein was studied in the springtail Orchesella c incta (Collembola), a species of insect living in forest soils. Upon dietar y exposure to Cd, two Cd-binding, cysteine-rich peptides were isolated from whole-body homogenates, using gel filtration and reversed-phase FPLC. Mass spectrometric analysis revealed that the molecular masses of these peptide s were 2989 Da and 4139 Da, respectively. Amino acid sequencing of the 2989 -Da peptide resulted in a sequence typical for a metallothionein. Sequencin g of the 4139-Da protein was unsuccessful, probably due to N-terminal block age. Using different PCR techniques (3' and 5' RACE) with (degenerate) prim ers based on the identified amino acid sequence of the 2989 Da peptide, a m etallothionein cDNA was isolated. The sequence of this cDNA potentially cod es for a protein of 77 amino acids. The 2989 Da peptide corresponds to the C-terminal part of this protein. The 4139-Da protein is probably encoded by the N-terminal part of this protein. These results suggest that the identi fied peptides ape products of one gene, and that the primary gene product i s subject to post-translational processing. The deduced amino acid sequence of the O. cincta metallothionein shows low sequence similarity with metall othioneins from Drosophila. The similarity between O. cincta MT and MTs of invertebrates is not higher than that between O. cincta and vertebrates.