The SCAN domain of ZNF174 is a dimer

The SCAN domain is a conserved region of 84 residues found predominantly in zinc finger DNA-binding proteins in vertebrates. The SCAN domain appears to control the association of SCAN domain containing proteins into noncovalent complexes and may be the primary mechanism underlying partner choice in the oligomerization of these transcription factors. Here we have overexpressed, purified, and characterized the isolated SCAN domain (amino acids 37-132) from ZNF174. Both size exclusion chromatography and equilibrium sedimentation analysis demonstrate that the ZNF174 SCAN domain forms a homodimer. Circular dichroism shows that the isolated SCAN domain dimer has approximately 42% alpha-helix. Thermal denaturation experiments indicate that the SCAN domain undergoes a single reversible unfolding transition with a T(m) of over 70 degrees C. The midpoint of the equilibrium unfolding transition increases with increasing protein concentration, consistent with a two-state unfolding transition in which folded dimer is in equilibrium with unfolded monomer. These findings demonstrate that the isolated SCAN domain forms a stable dimer and support a model in which the SCAN domain is capable of mediating the selective dimerization of a large family of vertebrate-specific, zinc finger-containing transcription factors.