The tumor suppressor protein p53 is a transcription factor that plays a major role in preventing cancer initiation and progression. Cellular stress conditions such as hypoxia or DNA damage activate p53, which induces cell cycle arrest, DNA repair, senescence, or apoptosis 
. In most, if not all, human cancers, the p53 apoptosis pathway is inactivated, and p53 itself is mutated in about half of all human cancers. About three-quarters of tumors with mutant p53 express full-length p53 with single missense mutations in the p53 DNA-binding core domain. These mutations may cause partial or global protein destabilization, loss of zinc coordination, or disruption of DNA contacts, and thus inactivate the tumor suppressor function of p53 (www-p53.iarc.fr
. These missense mutations (“cancer mutations” or “oncogenic mutations”) are widely distributed throughout the core domain (). They have been classified based on their physical location within the protein: (i) DNA-contact mutants (e.g., R248Q, R273H), (ii) structural mutants in the DNA binding surface (e.g., R175H, G245S, R249S, R282W), (iii) β-sandwich mutants (e.g., Y220C), and (iv) zinc-binding domain mutants (e.g., C242S, R175H).
Pharmacological rescue of p53 function in cancer tissues is an attractive therapeutic target 
. Recently, two independent studies on transgenic mice demonstrated that restoration of p53 activity enables tumor regression in vivo 
. p53 reactivation is especially promising in regression of advanced stage cancers 
. The p53 function of some oncogenic mutants has been rescued in vivo
by a handful of small molecules 
as well as by second-site suppressor (“cancer rescue”) mutations 
. The second-site mutations provide easily-studied cases of p53 cancer rescue.
The effect of oncogenic and rescue mutations in p53 has been of great interest. Many detailed structural studies have been pursued, including X-ray crystal structures of individual oncogenic and rescue mutants of p53 
. The loss or gain of hydrogen-bonding interactions, salt bridges and other minute stabilizing or destabilizing effects upon different missense mutations have been investigated to develop a more complete understanding of the inactivation mechanisms by the oncogenic missense mutations and, correspondingly, the mechanisms by which restoration of activity for rescue mutations occur 
. At 310 K, wild-type p53 is estimated to be only 3.0 kcal/mol more stable than the denatured state 
, and thus missense mutations can easily shift the delicate balance of p53 stability.
The present study quantifies the effect of oncogenic and rescue mutations on the overall dynamics of p53 without focusing on local structural details. The core DNA-binding domain of p53 was used, as it dictates the stability of the overall protein 
. The overall protein flexibility of the p53 DNA-binding domain for the wild-type, cancer mutants, rescue mutants and non-rescue mutants was compared in explicitly-solvated all-atom molecular dynamics (MD) trajectories, which are well suited to investigate the local conformational space sampled by each particular mutant. A single discriminating metric, the measure of flexibility of p53 in terms of the number of clusters obtained at a certain RMSD cutoff, was able to predict the functional activity of various mutant p53 proteins.