Metallothionein, family 4, echinoidea (IPR001396)

Short name: Metalthion_4_echinoidea

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].

Echinoidea (sea urchin, family 4) MTs are 64-67 residue proteins. Members of this family are recognised by the sequence pattern P-D-x-K-C-[V,F]-C-C-x(5)-C-x-C-x(4)-C-C-x(4)-C-C-x(4,6)-C-C located near the N terminus. The taxonomic range of the members extends to sea urchins (echinodea). The protein sequence is divided into two structural domains, each containing 9 and 11 Cys residues binding 3 and 4 bivalent metal ions, respectively. Family 4 includes subfamilies: e1, e2, they are separate phylogenetic groups.

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.