Identification of the metal coordinating residues in the DNA binding domain of the glucocorticoid receptor by 113Cd‐1H heteronuclear NMR spectroscopy

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Abstract
Two-dimensional 1H-113Cd HSQC and relay HSQC experiments were performed on the 113Cd substituted DNA binding domain of the rat glucocorticoid receptor. The results of these experiments combined with sequence-specific assignments allowed the identification of all coordinating cysteines.It was found that C495 and not C500 is the fourth coordinating cysteine in the second zinc-finger. A signal at ∼2 ppm previously assigned to a ε-CH3 of a methionine residue coordinating to a third, weakly bound, cadmium ion, was identified as the C443 β proton ligating to the metal ion in the first zinc-finger. No indications were found for the presence of a previously suggested third metal ion binding site.