The HPV16 E7 oncoprotein can form sphere-like particles that resemble RING proteins

ALONSO LEONARDO G.

Bariloche (Argentina)

Congreso; XXXIX annual meeting (SAIB) and Protein Symposium; 2003

High risk HPV16 E7 oncoprotein is an extended dimer capable of  undergoing pH dependent conformational transitions that expose hydrophobic surfaces to the solvent. The dimer shares some properties with intrinsically disordered proteins but it is clearly structured.  We found that it is capable of forming highly ordered soluble aggregates that elute in the void volume of a gel filtration column. Dynamic light scattering showed monodispersity and molecular weight of 790 kDa, with a radius of 26 nm assuming a globular architecture. Indeed, electron microscopy and atomic force microscopy showed regular and apparently homogeneous sphere- like particles of 40 to 50 nm diameter. The protein undergoes a conformational transition upon formation of these particles, with a substantial increase in â-sheet content as judged by circular dichroism. We introduced a tryptophan residue at position 98, present in the HPV18 E7 protein, and used it as probe for fluorescence studies that indicate an increase in tertiary (and quaternary) structure, also supported by near-UV CD spectra. These structures bind and shift congo red spectra and bind thioflavin T, the standard probes for amyloid structures. However, no insoluble material is formed under any condition tested. The assembly is very slow (t1/2 20 min), which will eventually allow the dissection of the mechanism.