CIRCULAR-DICHROISM STUDY ON THE CONFORMATIONAL STABILITY OF THE DIMERIZATION DOMAIN OF TRANSCRIPTION FACTOR LFB1

LFB1, a dimeric DNA binding protein, is a major determinant of hepatocyte-specific transcription. The thermal and chemical equilibrium unfolding of a 32-residue alpha-helical peptide comprising its dimerization domain (B1-Dim) was monitored by circular dichroism spectroscopy. The conformational stability of this peptide is shown to be concentration dependent, and the unfolding reaction is described as a two-state transition between folded dimers and unfolded monomers. The thermodynamic parameters associated with the unfolding reaction were determined under the two-state assumption by the van't Hoff procedure. The enthalpy of unfolding increases linearly with temperature, and the corresponding value of delta-C(p), the difference in heat capacity between the unfolded and the folded forms of the peptide, is estimated bo be ca. 0.7 kcal mol-1 K-1. The dimeric folded structure of the peptide is stabilized, at 25-degrees-C, by a delta-G of about 11.5 kcal mol-1, which is equivalent to a dimerization constant greater than 10(8) mol-1. These results indicate that the dimerization domain of LFB1 can fold and dimerize independently of the rest of the protein, with a thermodynamic stability comparable to that of a small globular protein.