Copper is an essential element for all living organisms since it is required as a catalytic cofactor for the functions of many redox enzymes.1,2 However, excess or free copper is toxic and must be strictly controlled. Regulation systems exist in biology for efficient control of copper binding and transport in living cells. Disorders in these systems are linked to diseases such as Menkes-Wilson’s diseases, Alzheimer’s and Parkinson’s.
Intracellular components of copper regulation predominantly employ cysteines as thiolate ligands for Cu(I). These protein thiols are subject to oxidative damage and are frequently protected as glutathionylated form that may be translated to a protein internal disulfide bond. Either form has little affinity for Cu(I). Consequently, reversible glutathionylation of protein thiols constitutes an important mechanism for regulation of Cu binding and transport. Human glutaredoxin 1 (hGrx1) is a key enzyme involved in this process (reaction below).3,4 However, the mechanism is not known in details.
Recent work demonstrated that copper induces molecular interaction between hGrx1 and many Cu(I)-binding proteins.5 Our study revealed an unexpected dual-function of hGrx1 as a redox enzyme and a Cu(I)-binding protein. Intriguingly, high affinity Cu(I) binding requires an intact active site motif CxxC but the redox activity relies on a single cysteine only. In fact, Cu(I) binding suppresses the enzyme activity while removal of the internal cysteine at active site weakens Cu(I) binding but enhances the enzyme function. These observations provide new insight into a possible mechanism of copper regulation via sulfur redox chemistry.