Posttranslational modifications affect the interaction of S100 proteins with tumor suppressor p53

Proteins of the S100 family bind to the intrinsically disordered transactivation domain (TAD; residues 1-57) and C-terminus (residues 293-393) of the tumor suppressor p53. Both regions provide sites that are subject to posttranslational modifications, such as phosphorylation and acetylation, that can alter the affinity for interacting proteins such as p300 and MDM2. Here, we found that S100A1, S100A2, S100A4, S100A6, and S100B bound to two subdomains of the TAD (TAD1 and TAD2). Both subdomains were mandatory for high-affinity binding to S100 proteins. Phosphorylation of Ser and Thr residues increased the affinity for the p53 TAD. Conversely, acetylation and phosphorylation of the C-terminus of p53 decreased the affinity for S100A2 and S100B. In contrast, we found that nitrosylation of S100B caused a minor increase in binding to the p53 C-terminus, whereas binding to the TAD remained unaffected. As activation of p53 is usually accompanied by phosphorylation and acetylation at several sites, our results suggest that a shift in binding from the C-terminus in favor of the N-terminus occurs upon the modification of p53. We propose that binding to the p53 TAD might be involved in the stimulation of p53 activity by S100 proteins.