Metallothionein 1 (MT1)

In man, metallothioneins are encoded by at least 10 to 12 genes separated into 2 groups designated MT-I and MT-II. Masters et al. (1994) noted that, unlike MT-I and MT-II, which are expressed in most organs, MT-III  expression appears to be restricted to the brain, and MT-IV is only expressed in certain stratified squamous epithelia.

Class I metallothioneins contain 2 metal-binding domains: four divalent ions are chelated within cluster A of the alpha domain and are coordinated via cysteinyl thiolate bridges to 11 cysteine ligands. Cluster B, the corresponding region within the beta domain, can ligate three divalent ions to 9 cysteines.