CopK is a periplasmic dimeric protein which is strongly up-regulated in the presence of copper, leading to a high periplasmic accumulation [1]. CopK has two different binding sites for Cu(I), each with a different affinity for the metal. Binding of the first Cu(I) ion induces a conformational change of CopK which involves dissociation of the dimeric apo-protein. Binding of a second Cu(I) further increases the plasticity of the protein. CopK has features that are common with functionally related proteins such as a structure consisting of an all-beta fold and a methionine-rich Cu(I) binding site [1].

1: Molecular structure and metal-binding properties of the periplasmic CopK protein expressed in Cupriavidus metallidurans CH34 during copper challenge. Bersch B, Favier A, Schanda P, van Aelst S, Vallaeys T, Coves J, Mergeay M, Wattiez R; J Mol Biol. 2008;380:386-403. PMID:18533181