Identification of energy landscape of Sp1 zinc-finger in Pb(II) or Cd(II) using AFM

The interaction between the zinc finger transcription factor (ZF-TF) and a specific DNA sequence is characterized by energy landscape parameters such as the dissociation rate constant and binding free energy. Heavy metals, such as lead (Pb) and cadmium (Cd), disturb transcription processes by changing the DNA-binding affinities of ZF-TF. To investigate the interference of heavy-metal ions with DNA transcription, we determined the unbinding force between ZF-TF and DNA by atomic force microscopy (AFM). The results suggest that the binding affinity of this complex is stronger in Pb(II) solution than under normal conditions, while the binding affinity in Cd(II) solution is weaker than under normal conditions. Thus, ZF-TF is an important target for heavy metal poisoning. Gold (Au) has a high affinity with cysteine residues, and so, it effectively coordinates with ZF-TF. AFM was employed to detect the molecular interaction force between ZF-TF and DNA in an Au(I) environment. Data analysis demonstrated that Au(I) helps restore normal binding affinity. The measurement of the unbinding force enabled us to quantify the binding free energy in the dissociation process. Alterations of kinetic parameters, which describe the energy landscape, are associated with metal poisoning disease and can be used to screen drugs for heavy-metal induced disease.