Metallothionein, mollusc (IPR001008)

Short name: Metalthion_mollusc

Overlapping homologous superfamilies


Family relationships



Metallothioneins (MT) are small proteins that bind heavy metals, such as zinc, copper, cadmium, nickel, etc. They have a high content of cysteine residues that bind the metal ions through clusters of thiolate bonds [PMID: 1779825, PMID: 2959513]. An empirical classification into three classes has been proposed by Fowler and coworkers [PMID: 2959504] and Kojima [PMID: 1779826]. Members of class I are defined to include polypeptides related in the positions of their cysteines to equine MT-1B, and include mammalian MTs as well as from crustaceans and molluscs. Class II groups MTs from a variety of species, including sea urchins, fungi, insects and cyanobacteria. Class III MTs are atypical polypeptides composed of gamma-glutamylcysteinyl units [PMID: 2959504].

This original classification system has been found to be limited, in the sense that it does not allow clear differentiation of patterns of structural similarities, either between or within classes. Subsequently, a new classification was proposed on the basis of sequence similarity derived from phylogenetic relationships, which basically proposes an MT family for each main taxonomic group of organisms [PMID: 21633816].

Mollusc MTs are 64-75 residue proteins. They usually contain 18-23 Cys, at least 13 of them are totally conserved. The protein sequence is divided into two structural domains. The Cys residues are arranged in C-X-C groups, and a C-X-X-C grouping is also observed. In particular, the consensus pattern C-x-C-x(3)-C-T-G-x(3)-C-x-C-x(3)-C-x-C-K has been shown to be diagnostic of family 2 metallothioneins. MTs locate at the C terminus of the sequence. These proteins show more similarily to the vertebrate metallothioneins than to those from other invertebrate phyla [PMID: 2774559], and on this basis they are classified as class I metallothioneins. The protein is induced by cadmium and binds divalent cations of several transition elements, including cadmium, zinc and copper. Family 2 includes subfamilies: mo1, mo2, mog, mo, which hit the same entry, except the subfamily mog.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0046872 metal ion binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.