THE DIMERIC DNA-BINDING DOMAIN OF THE HUMAN PAPILLOMAVIRUS E2 PROTEINFOLDS THROUGH A MONOMERIC INTERMEDIATE WHICH CANNOT BE NATIVE-LIKE

The dimeric DNA binding domain of the human papillomavirus E2 protein displays a two-state concerted unfolding and dissociation, with no det ectable monomeric intermediate species accumulated at equilibrium. We investigated the kinetic folding mechanism of the dimeric domain using stopped-flow spectroscopic techniques and observed a fast forming mon omeric intermediate, followed by a slower bimolecular reaction. Both p hases involve secondary structure rearrangements of similar magnitude. Our results support a folding pathway in which the formation of an ea rly monomeric intermediate, with characteristics of hydrophobic collap se, is followed by a bimolecular step encompassing association and fol ding. The interwoven folding topology of this particular type of dimer ic P-barrel found in the E2 DNA binding domain strongly suggests that any monomeric species formed could not be native-like.