The Ca(2+)-dependent interaction of S100B(beta beta) with a peptide derived from p53

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Interactions

Background:

• S100B(beta beta) protein is known to interact with the tumor suppressor protein p53.
• This interaction inhibits p53's protein kinase C (PKC)-dependent phosphorylation and tetramer formation.
• PKC-dependent phosphorylation at p53's C-terminus influences its transcriptional activity and tetramerization.

Purpose of the Study:

• To investigate the interaction between S100B(beta beta) and a peptide from p53's C-terminal regulatory domain (residues 367-388).
• To elucidate the mechanism by which S100B(beta beta) inhibits p53 phosphorylation.

Main Methods:

• Calcium titration and fluorescence spectroscopy to determine binding affinity.
• Electron Paramagnetic Resonance (EPR) and Pulse Radiolysis (PRR) to study Ca2+ binding.
• Nuclear Magnetic Resonance (NMR) spectroscopy to identify binding sites.

Main Results:

• S100B(beta beta) binds to the p53 peptide in a Ca(2+)-dependent manner with a dissociation constant (K(d)) of 23.5 +/- 6.6 microM.
• The p53 peptide enhances Ca2+ binding affinity to S100B(beta beta) by 3-fold, but does not affect Zn2+ binding.
• NMR data indicate that the p53 peptide binds to specific regions of S100B(beta beta), including the hinge, C-terminal loop, and helix 3.

Conclusions:

• S100B(beta beta) directly binds to the C-terminus of p53.
• This direct interaction is responsible for inhibiting PKC-dependent phosphorylation of p53.
• The findings provide a molecular basis for S100B(beta beta)'s role in regulating p53 function.