Binding Site

Metallothionein, vertebrate, metal binding site (IPR018064)

Short name: Metalthion_vert_metal_BS

Description

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].

The members of family 1 are recognised by the sequence pattern K-x(1,2)-C-C-x-C-C-P-x(2)-C located at the beginning of the third exon. The taxonomic range of the members extends to vertebrates. Known characteristics: 60 to 68 AAs; 20 Cys (21 in one case), 19 of them are totally conserved; the protein sequence is divided into two structural domains, containing 9 and 11 Cys all binding 3 and 4 bivalent metal ions, respectively. The gene is composed of 3 exons, 2 introns and the splicing sites are conserved. Family 1 includes subfamilies: m1, m2, m3, m4, m, a, a1, a2, b, ba, t, all of them hit the same InterPro entry.

This entry represents a conserved region containing seven of the metal-binding cysteines, located in the N-terminal section of family 1 MTs.

Contributing signatures

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