Metallothioneins are characterised by an abundance of cysteine residues and a lack of generic secondary structure motifs. This protein functions in primary metal storage, transport and detoxification [1]. For the first 40 residues in the protein the polypeptide wraps around the metal by forming two large parallel loops separated by a deep cleft containing the metal cluster [1].

1: 3D solution structure of copper and silver-substituted yeast metallothioneins. Peterson CW, Narula SS, Armitage IM; FEBS Lett. 1996;379:85-93. PMID:8566237