Metal-dependent folding of a single zinc finger from transcription factor IIIA

A 30-amino acid peptide, which corresponds to the second "zinc finger" domain of transcription factor IIIA, has been synthesized and purified. This peptide folds in the presence of zinc: adding Zn2+ significantly changes the circular dichroism spectrum, and Zn2+ protects the peptide from tryptic digestion. The peptide also binds Co2+, and the absorption spectrum of the Co2+ complex suggests that a tetrahedral binding site is formed by two cysteines and two histidines. Experiments at higher temperatures (60-75 degrees C) suggest that these folded metal-peptide complexes are quite thermostable. The peptide shows some sequence-specific effects in DNase and methylation protection experiments. However, it does not give a clear "footprint," and some effects are observed in the absence of added zinc.