Protein intrinsic disorder and human papillomaviruses: Increased amount of disorder in E6 and E7 Oncoproteins from high risk HPVs

It is recognized now that many functional proteins or their long segments are devoid of stable secondary and/or tertiary structure and exist instead as very dynamic ensembles of conformations. They are known by different names including natively unfolded, intrinsically disordered, intrinsically unstructured, rheomorphic, pliable, and different combinations thereof. Many important functions and activities have been associated with these intrinsically disordered proteins (IDPs), including molecular recognition, signaling, and regulation. It is also believed that disorder of these proteins allows function to be readily modified through phosphorylation, acetylation, ubiquitination, hydroxylation, and proteolysis. Bioinformatics analysis revealed that IDPs comprise a large fraction of different proteomes. Furthermore, it is established that the intrinsic disorder is relatively abundant among cancer-related and other disease-related proteins and IDPs play a number of key roles in oncogenesis. There are more than 100 different types of human papillomaviruses (HPVs), which are the causative agents of benign papillomas/ warts, and cofactors in the development of carcinomas of the genital tract, head and neck, and epidermis. With respect to their association with cancer, HPVs are grouped into two classes, known as low (e.g., HPV-6 and HPV-11) and high-risk (e.g., HPV-16 and HPV-18) types. The entire proteome of HPV includes six nonstructural proteins [E1, E2, E4, E5, E6, and E7 (the latter two are known to function as oncoproteins in the high-risk HPVs)] and two structural proteins (L1 and L2). To understand whether intrinsic disorder plays a role in the oncogenic potential of different HPV types, we have performed a detailed bioinformatics analysis of proteomes of high-risk and low-risk HPVs with the major focus on E6 and E7 oncoproteins. The results of this analysis are consistent with the conclusion that high-risk HPVs are characterized by the increased amount of intrinsic disorder in transforming proteins E6 and E7.