Conformational dissection of a viral intrinsically disordered domain involved in cellular transformation

PLoS One. 2013 Sep 27;8(9):e72760. doi: 10.1371/journal.pone.0072760. eCollection 2013.

Abstract

Intrinsic disorder is abundant in viral genomes and provides conformational plasticity to its protein products. In order to gain insight into its structure-function relationships, we carried out a comprehensive analysis of structural propensities within the intrinsically disordered N-terminal domain from the human papillomavirus type-16 E7 oncoprotein (E7N). Two E7N segments located within the conserved CR1 and CR2 regions present transient α-helix structure. The helix in the CR1 region spans residues L8 to L13 and overlaps with the E2F mimic linear motif. The second helix, located within the highly acidic CR2 region, presents a pH-dependent structural transition. At neutral pH the helix spans residues P17 to N29, which include the retinoblastoma tumor suppressor LxCxE binding motif (residues 21-29), while the acidic CKII-PEST region spanning residues E33 to I38 populates polyproline type II (PII) structure. At pH 5.0, the CR2 helix propagates up to residue I38 at the expense of loss of PII due to charge neutralization of acidic residues. Using truncated forms of HPV-16 E7, we confirmed that pH-induced changes in α-helix content are governed by the intrinsically disordered E7N domain. Interestingly, while at both pH the region encompassing the LxCxE motif adopts α-helical structure, the isolated 21-29 fragment including this stretch is unable to populate an α-helix even at high TFE concentrations. Thus, the E7N domain can populate dynamic but discrete structural ensembles by sampling α-helix-coil-PII-ß-sheet structures. This high plasticity may modulate the exposure of linear binding motifs responsible for its multi-target binding properties, leading to interference with key cell signaling pathways and eventually to cellular transformation by the virus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Transformation, Neoplastic*
  • Circular Dichroism
  • Hydrogen-Ion Concentration
  • Intrinsically Disordered Proteins / chemistry*
  • Molecular Sequence Data
  • Nuclear Magnetic Resonance, Biomolecular
  • Oncogene Proteins, Viral / chemistry*
  • Papillomaviridae / chemistry*
  • Protein Conformation
  • Spectrophotometry, Ultraviolet

Substances

  • Intrinsically Disordered Proteins
  • Oncogene Proteins, Viral

Grants and funding

Instituto Nacional del Cancer-Ministerio de Salud-Argentina (Basic Research Grant 2012–2014) (http://www.msal.gov.ar/inc/). MGN holds a graduate fellowship from Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET). MG, AGS, LBC and GPG are career researchers from CONICET. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.