The HPV16 E7 oncoprotein can form supramolecular structures

LEONARDO G. ALONSO; MARIA M. GARCÍA-ALAI; RUBÉN IACONO; EDUARDO CASTAÑO; PETER GUALFETTI; GONZALO DE PRAT-GAY

Trieste (Italia)

Congreso; DNA Tumor Virus Meeting; 2003

ICGEB

The E7 oncoprotein from the high risk strain 16 is an extended dimer capable of undergoing  pH dependent conformational transitions that expose hydrofobic surfaces to the solvent. The dimer shears some properties with intrinsically disordered proteins but it is clearly structured. We find that it is capable of forming highly soluble aggregates that elute in the void volume of a gel filtration column. Using dynamic Light scattering we determined a molecular weight of 790 kDa and observed monodispersity, we a radius pf 26 nm assuming a globular architecture. SDS PAGE analyses indicated that despite E7 Cys residues present in the protein no intermolecular disulfide bonds are formed in the oligomer. The protein undergoes a conformational transition upon formation of these aggregates, with a substantial increase in beta sheet content as judged by CD. We introduced a tryptophan residue at position 98, present in the HPV18 E7 protein, and used it as probes for fluorescence studies that indicate an increase in tertiary (and cuaternary) structure, also supported by near-UV CD spectra. These soluble aggregates also bind and shift congo red absorbance spectra and bind thioflavin T, the Standard probes for amyloid structures. However, no insoluble material is formed under any condition tested.