The N-Terminal Domain of the HPV16 E7 Oncoprotein Displays Residual and Extended Structure with Poly(L-Proline) Type II Characteristics in Solution

MARIA GARCIA-ALAI; L. ALONSO; TOMMASO ELISEO; CICERO DANIEL; G. DE PRAT GAY

Bariloche (Argentina)

Congreso; XXXIX, anual meeting and Protein Symposium; 2003

HPV16 E7 oncoprotein is an extended and hyperstable dimer and undergoes conformational transtions by pH change, with exposure of hydrophobic surfaces that could facilitate protein-protein recognition of its multimple cellular partners.  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 domains and we have evidence that many of the biochemical properties of E7 are dictated by the N-terminal domain. We present the characterization of the E7(1-40) N-terminal domain, displaying disordered CD and NMR spectra at neutral pH. At low pH (4.0) the peptide shows an increased a-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 a-helix while sub-micellar concentrations induce ß-sheet structures. Solvent mediated transitions are clearly pH dependent indicating that the neutralization of the several acidic residues must be involved, suggesting that similar transitions might take place in the cell