Deciphering the mechanisms of HPV E6 mutations in the destabilization of E6/E6AP/p53 complex

In epithelial tumors, oncoprotein E6 binds with the ubiquitin ligase E6AP to form E6/E6AP heterodimer; then this heterodimer recruits p53 to form E6/E6AP/p53 heterotrimer and induces p53 degradation. Recent experiments demonstrated that three E6 single-site mutants (F47R, R102A, and L50E) can inhibit the E6/E6AP/p53 heterotrimer formation and rescue p53 from the degradation pathway. However, the molecular mechanism underlying mutation-induced heterotrimer inhibition remains largely elusive. Herein, we performed extensive molecular dynamics simulations (totally ∼13 μs) on both heterodimer and heterotrimer to elucidate at an atomic level how each p53-degradation-defective HPV16 E6 mutant reduces the structural stabilities of the two complexes. Our simulations reveal that the three E6 mutations destabilize the structure of E6/E6AP/p53 complex through distinct mechanisms. Although F47R^E6 mutation has no effect on the structure of E6/E6AP heterodimer, it results in an electrostatic repulsion between R47^E6 and R290^p53, which is unfavorable for E6-p53 binding. R102A^E6 mutation destabilizes the structure of E6/E6AP heterodimer and significantly disrupts hydrophobic and cation-π interactions between F47^E6 and E286^p53/L298^p53/R290^p53. L50E^E6 mutation impairs both E6 interdomain interactions (especially F47-K108 cation-π interaction) and E6-E6AP intermolecular interactions important for the stabilization of E6/E6AP heterodimer. This study identifies the intra- and intermolecular interactions crucial for the complex stability, which may provide mechanistic insights into the inhibition of complex formation by the three HPV16 E6 mutations.