Metallothioneins have a high content of cysteine residues that bind various heavy metals (Probable). Functions as metal chelator of nickel (Ni), cadmium (Cd), zinc (Zn) and copper (Cu). Possesses higher affinity for Ni and Cd ions compared to Zn and Cu ions (PubMed:23385446). Expressed in leaves of mature plants. Belongs to the metallothionein superfamily. Type 15 family.