Different Oligomeric States of the Tumor Suppressor p53 Show Identical Binding Behavior towards the S100 beta Homodimer

The tumor suppressor protein p53 is a transcription factor that is referred to as the "guardian of the genome" and plays an important role in cancer development. p53 is active as a homotetramer; the S100 beta homodimer binds to the intrinsically disordered C-terminus of p53 affecting its transcriptional activity. The p53/S100 beta complex is regarded as highly promising therapeutic target in cancer. It has been suggested that S100 beta exerts its oncogenic effects by altering the p53 oligomeric state. Our aim was to study the structures and oligomerization behavior of different p53/S100 beta complexes by ESI-MS, XL-MS, and SPR. Wild-type p53 and single amino acid variants, representing different oligomeric states of p53 were individually investigated regarding their binding behavior towards S100 beta. The stoichiometry of the different p53/S100 beta complexes were determined by ESI-MS showing that tetrameric, dimeric, and monomeric p53 variants all bind to an S100 beta dimer. In addition, XL-MS revealed the topologies of the p53/S100 beta complexes to be independent of p53's oligomeric state. With SPR, the thermodynamic parameters were determined for S100 beta binding to tetrameric, dimeric, or monomeric p53 variants. Our data prove that the S100 beta homodimer binds to different oligomeric states of p53 with similar binding affinities. This emphasizes the need for alternative explanations to describe the molecular mechanisms underlying p53/S100 beta interaction.