Question

Zinc fingers are common protein structural motifs that can bind DNA, RNA, or other proteins. The metal binding site is often comprised of two cysteine residues and two histidine residues. One mechanism of cadmium poisoning involves substitution of Cd(II) for Zn(II) in zinc fingers. Explain why it would be favorable for Cd(II) to substitute for Zn(II) in zinc fingers.

Answer 1

Zn fingers contains thiol groups in their cystein residues. Due to the presence of these thiol groups, the residues will have a strong affinity towards softand boderline metal ions. Zn is a metal of borderline softness whereas cadmium is a soft metal. In terms of affinity towards S and N containing ligands, Cd has a higher affinity than Zn. Due to this, Zn gets displaced by Cd in zinc fingers. The displacement can lead to inhibition of activities of Zn fingers. This happens during cadmium poisoning.