Zinc coordination scheme for the C-terminal zinc binding site of nuclear hormone receptors

The DNA-binding domain of the glucocorticoid receptor contains two zinc ions which are important for the structure and function of the protein. The zinc ions are tetrahedrally coordinated by cysteine residues within the DNA-binding domain. The DNA-binding domain of the glucocorticoid receptor, as well as of the other nuclear hormone receptors, contains nine highly conserved cysteine residues. It has not been clearly established which of these nine cysteine residues are involved in the coordination of zinc. Two models have been proposed for the zinc coordination scheme. We present evidence in flavour of the model which excludes the most C-terminal cysteine residue (Cys-481 of the human glucocorticoid receptor) from the zinc coordination scheme. Mutation of this residue in the context of the glucocorticoid receptor DNA-binding domain expressed in E. coli does not significantly reduce the structural integrity of the protein or its DNA-binding properties. These in vitro results are also confirmed by in vivo transactivation assays in yeast.