Metallothioneins

Metallothioneins are a group of small proteins, which are extremely rich in cysteine. They are used for the transport and storage of soft, "thiophilic" metal ions like Zn²⁺ and Cu²⁺.

They are also used to remove toxic ions like Hg²⁺ and Cd²⁺ from cells.

The metal ions can be bound in different ways. Both tetrahedrally bound, isolated metal ions and clusters of metal ions can be found, as is shown here.

  Coordination of the Zn²⁺ ions in cluster I

  Coordination of the Zn²⁺ ions in cluster II