Conformational transitions in the N-terminal domain of the HPV16 E7 oncoprotein in solution

MARIA M. GARCIA-ALAI; LEONARDO G. ALONSO; G. DE PRAT GAY

Triete (Italia)

Congreso; DNA Tumor Virus Meeting; 2003

ICGEB

HPV16 E7 oncoprotein undergoes conformational transitions by pH, with exposure of hydrophobic surfaces that could facilitate protein-protein recognition.  The protein is composed of a highly acidic N-terminal domain and a zinc containing C-terminal domain. E7 from high and low cancer risk HPV strains differ mainly in their N-terminal domain, which contains the Rb binding domain and the Casein Kinase II phosphorylation site. We have evidence that many of the biochemical properties of E7 are dictated by the N-terminal domain. The E7(1-40) N-terminal domain characterized here, displays apparently disordered CD and NMR spectra at neutral pH. At low pH (4.0) the peptide shows an increased alpha-helix content, in agreement with the full protein. Large increase in helical content upon addition of trifluoroethanol is obtained at pH 4.0 but not at pH 7.0, suggesting a persistent residual structure at pH 7.0. Micellar SDS concentrations induce alpha-helix while sub-micellar concentrations induce beta-sheet structures.  Solvent mediated transitions are clearly pH dependent within physiological values indicating that the neutralization of the several acidic residues must be involved, and suggesting that similar transitions might take place in the cell.  The N-terminal fragment can be phosphorylated in vitro by casein kinase II, to a similar extent as the full E7 protein..