The zinc finger motif belonging to the Cys(2)/His(2) family provides a structural framework for a number of critical proteins which are essential for cellular function. To determine whether these domains are potential targets for heavy metal perturbation, we examined the interaction between various metals and a synthetic Cys(2)/His(2) finger peptide, of the type present in the transcription factor Sp1 and an intact recombinant human Sp1 protein (rhSp1). Sp1 has a DNA-binding domain composed of three contiguous zinc finger motifs which requires Zn(II) for its activity, and may be modulated by other transition metals. Using spectrophotometric methods, the incorporation of Zn(II) and a variety of other divalent metals into this zinc finger peptide was monitored, and their ability to displace zinc ion was evaluated. Furthermore, the DNA-binding activity of these various metal-peptide complexes and rhSp1 to their cognate DNA consensus sequence was examined electrophoretically. Our results suggested that group IIb metals [Zn(II), Cd(II), and Hg(II)] were able to complex with the peptide and bind the double-stranded DNA with high affinity as well as inhibiting Sp1 DNA-binding activity in a concentration-dependent manner. With the exception of Pb(II), non-transition-metal-peptide mixtures with Ca(II), Ba(II), and Sn(II) neither exhibited the binding spectra typical of zinc finger motifs nor bound the DNA; they also had little effect on DNA-binding ability of rhSp1. Therefore, we postulate that heavy metals may modulate zinc finger proteins through structural alterations of their zinc finger motifs and ultimately alter their function in terms of regulation of gene expression.
Copyright 2000 Academic Press.