Thermodynamic characterization of the structural stability of the coiled-coil region of the bZIP transcription factor GCN4

The thermal stability of a 56 amino acid fragment of GCN4 has been studied by high-sensitivity differential scanning calorimetry and circular dichroism spectroscopy. This fragment contains the leucine zipper and part of the basic region. The thermal unfolding of GCN4-56 is a reversible process and can be well represented by a reaction of the form N 2 ↔2U, indicating that the unfolding of the leuzine zipper is a two-state process in which the helices are only stable when they are in the coiled-coil conformation. As expected, the transition temperature is concentration dependent