Structural and computational insights into the versatility of cadmium binding to proteins

Abstract

Cadmium is a highly toxic group XII metal, similar to zinc and mercury. Unlike zinc, which is one of the most common metal cofactors in biology, cadmium is highly toxic. Many Zn²⁺-binding proteins can bind Cd²⁺-ions without significantly affecting their structures. Here, the protein data bank is analysed with regard to protein–cadmium interactions, which shows that cadmium can bind to a variety of ion binding sites in proteins. Statistical analysis of Cd²⁺-side chain interactions is compared with a similar analysis of other ions. This analysis reveals that with regard to amino acid side-chain preference, Cd²⁺ is more similar to Mn²⁺ than to Zn²⁺ or Hg²⁺. Finally, the interaction energies of three native metal binding proteins are calculated where Cd²⁺ binds instead of Zn²⁺, Ca²⁺ or Cu²⁺. The interaction energies are decomposed into individual components whose contributions are discussed.