Altered Kinetics of p53 Caused by the Mutation P27A

Transient tertiary structures found in p53 NTAD. A) An example transient tertiary structure found for the P27A mutant in a 60 µs long simulation showing the lifetime, involved residues and the conformation. B) Heatmaps of tertiary structure lifetime versus involved residues based on all simulations of WT and P27A. Grey shaded areas indicate regions with experimentally known helical propensity.

© MPI-NAT Daniel Szöllösi

Transient tertiary structures found in p53 NTAD. A) An example transient tertiary structure found for the P27A mutant in a 60 µs long simulation showing the lifetime, involved residues and the conformation. B) Heatmaps of tertiary structure lifetime versus involved residues based on all simulations of WT and P27A. Grey shaded areas indicate regions with experimentally known helical propensity.

© MPI-NAT Daniel Szöllösi

Collaborations: Griesinger Lab @MPI-NAT NMR-Based Structural Biology

The protein p53 is also called the ‘guardian of the genome’ due to its central role in genetic stability. It interacts with numerous other proteins, mainly via its disordered N-terminal transactivation domain (NTAD). It has been shown that an α-helix can fold in the unbound NTAD from residue T18 to L26 which serves as one of the main interaction sites. Furthermore, the same helix has been found in stable protein complexes e.g. with MDM2. This helix is terminated by proline 27 (P27), a residue conserved in all mammalian organisms. Our collaborators NMR relaxation dispersion experiments revealed that mutation of P27 to alanine (P27A) drastically alters the measured kinetic timescale of the surrounding residues. Also, it has been shown that the same mutation also increases the binding affinity to MDM2 by 10-fold.

In order to elucidate the structural reasons for such a marked alteration, we did extensive molecular dynamics simulations totaling 0.6 ms for the WT and 1.8 ms for the P27A mutant p53. For both proteins the expected α-helix between residues T18 to L26 can be found, however for the P27A mutant with a significantly higher propensity (WT ~ 10% vs. P27A ~ 30%). Identification of transient tertiary structures in both peptides (Figure 1.) confirmed that the mutant visits longer-lived folded states, however, observed timescales in the molecular dynamics simulations are shorter compared to the NMR experiment. We suggest the reason for the structural changes is due to the increased conformational space opened by the mutation.