Zinc(II) holds diverse roles stabilizing protein structures and providing enzymatic activity. Glucocorticoid receptor DNA-binding domain (GR-DBD), a 91-residue zinc finger protein, binds two Zn2+, each coordinating four cysteines, to provide a compact structure that acts as a transcription factor for DNA recognition. The thermodynamics of Zn2+ binding GR-DBD are being determined to understand the favorability of the Zn2GR-DBD formation. Many spectroscopic techniques cannot be used to study Zn2+, a d10 metal ion, because it is spectroscopically silent, and the binding of Zn2+ to GR-DBD does not produce any color change. Isothermal titration calorimetry (ITC) is an attractive alternative that uses the changes of heat to determine the thermodynamics between Zn2+ and GR-DBD. Because of the tendency of apo-GR-DBD cysteine oxidation, a new approach looking at the thermodynamics of chelating out the Zn2+ from Zn2+-bound GR-DBD using EDTA was used. The thermodynamics of this Zn2+ chelation experiments is equal and opposite to Zn2+ binding GR-DBD, based on the principle of microscopic reversibility. The ITC experiments will provide insight towards the favorability of Zn2+ binding to GR-DBD and help determine if the Zn2GR-DBD formation is entropically or enthalpically driven. Further research will examine the thermodynamics of surrogates cobalt(II) and cadmium(II) binding GR-DBD to provide better understanding into how these the surrogate metal ions could interfere with physiological function.

Thermodynamics of Zn(II) and surrogate metal ions binding to the glucocorticoid receptor DNA-binding domain

251st National Meeting (2016)

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