Quantitative analysis of entropic tethering in a minimal viral model system

CHEMES LUCIA; CHEMES LUCIA

Les Diablerets

Conferencia; Gordon Conference on Intrinsically Disordered Proteins; 2018

Gordon Research Conferences

Viral hijack of cell regulation is achieved through complex interactions often involving multiple binding sites. The mechanisms through which viral proteins effectively outcompete host interactions remain largely unknown. In particular, the role played by intrinsically disordered linkers in determining the binding strength of systems with complex binding topologies is still unclear. We used the Adenovirus E1A protein as a minimal model system to approach this problem. E1A uses two binding motifs joined by a disordered ?linker? to bind to the Retinoblastoma (pRb) tumor suppressor, leading to cell cycle deregulation and transformation.Using an integrated biophysical NMR and modeling approach, we demonstrate flexibility within E1A is critical for maximal enhancement of binding strength, allowing the formation of an ultrahigh picomolar affinity complex. A random polymer model predicts the compound affinity with striking accuracy and is supported by experimental evidence that the E1A linker remains largely disordered in the complex, behaving as an entropic tether that optimally positions the motifs for binding to pRb. While the model predicts linker length is the main determinant for binding, biophysical data suggests the polymer-like behavior is realized through a fine tuned balance between repulsive interactions of the negatively charged linker and weak hydrophobic interactions at regions overlapping with secondary binding sites. This work suggests minimal models provide useful tools to describe disordered linkers in systems with complex binding topologies. The striking conservation of linker disorder, length and charge distribution suggests these features were selected throughout evolution to allow effective competition with cellular interactions.