How cells handle copper: A view from microbes

Copper is an essential element, yet toxic to cells. It can damage biomolecules by radical formation and, therefore, the intracellular copper needs to be carefully controlled. In the Gram-positive bacterium Enterococcus hirae, copper homeostasis is effected by the cop operon. It allows growth under copper limiting conditions, but also offers resistance to 8 mM copper. The cop operon consists of the four genes copY, copZ, copA, and copB. CopA and copB encode copper ATPases. CopA serves in copper uptake under copper limitation, whereas CopB expels copper when copper is excessive. CopA and CopB are closely related to the human Menkes and Wilson ATPases. Mutation in these human copper ATPases lead to inherited defects of copper metabolism, known as Menkes and Wilson disease, respectively. Copper ATPases and other heavy metal ATPases form a new, evolutionarily distinct subgroup of the P-type ATPases, called CPx-type ATPases. The cop operon of E. hirae is regulated by the copper responsive repressor CopY. Copper donated to CopY by the copper chaperone CopZ releases it from the promoter. CopZ belongs to a family of conserved metal chaperones that transfer copper to copper-transporting ATPases in humans and yeast (HAH1, Atx1), and mercury to a mercury uptake system in bacteria (MerP). CopZ-like motifs are also found in the N-termini of the CPx-type ATPases and mercuric reductases. A model of copper homeostasis and the role of copper chaperones in mammalian cells based on findings in yeast and E. hirae is presented. J. Trace Elem. Exp. Med. 12:347–360, 1999.