Metallothioneins have a high content of cysteine residues that bind various heavy metals. Probably involved in maintaining homeostasis of essential transition metals and detoxification of toxic metals. Increases cadmium and zinc tolerance when expressed in heterologous systems. Metal chelator binding 6 cadmium or 5 zinc atoms per protein. Expressed in leaves, stems and roots. Up-regulated by cadmium treatment. The N-terminal (1-23) and C-terminal (66-84) Cys-rich domains are both involved in zinc binding. Belongs to the metallothionein superfamily. Type 15 family.