Assembly of HPV16 E7 spherical oligomers is regulated by a redox mechanism

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

University of Wisconsin-Madison (USA)

Conferencia; The 2004 Molecular Biology of DNA Tumor Viruses Conference; 2004

Recombinant HPV16 E7, the major transforming protein in HPV, is a non-globular extended dimer with conformational transitions leading to increased exposure of hydrophobic surfaces, within a physiological pH range ().  Metal chelating agents promote the formation of spherical oligomers (E7SOs) of 790 kDa, confirmed by light scattering, electron microscopy and atomic force microscopy, by removing the strongly bound zinc atom.  We found that the E7 dimer is very sensitive to the redox state.  Oxidation of the E7 dimer leads to a significant conformational change that involves  burial of solvent accessible surface and zinc release, either by a physiological redox buffer (glutathion) or by the formation of free radicals from treatment with hydrogen peroxide.  The oxidation is a reversible process and released zinc can be recaptured.  The oxidized species does not form E7SOs under similar conditions where the reduced zinc containing E7 dimer would form.  E7SOs has strong tendency to oxidation, where only 3 out of 7 SH groups are titratable.  The fully oxidized oligomer is extremely stable, most likely crosslinked by s-s bridges.  The  redox potential, compatible with physiological values, together with the reversibility of the process suggests that the assembly of the oligomers, and E7 biological activity in general could be regulated by changes in the intracellular redox state.  This could be in response to redox signaling cascades or the formation of free radicals associated with oxidative stress often found in transformation processes.