Semisynthetic 'designer' p53 sheds light on a phosphorylation-acetylation relay

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• The tumor suppressor protein p53 is crucial for regulating cell fate.
• p53 activity is modulated by numerous posttranslational modifications (PTMs), but their regulatory mechanisms remain unclear due to limited studies on specifically modified p53.
• Understanding p53 regulation is vital for cancer research and therapy.

Purpose of the Study:

• To develop a protein semi-synthesis approach for generating site-specifically modified p53.
• To biochemically characterize p53 variants with defined phosphorylation marks.
• To investigate the functional impact of N-terminal phosphorylation on p53 activity.

Main Methods:

• Protein semi-synthesis was employed to create full-length p53 with defined phosphorylation sites (Ser20ph, Ser15ph, or Ser15,20ph).
• Chemically homogeneous p53 variants were synthesized and refolded.
• Biochemical characterization, including p300-dependent acetylation assays, was performed on the semisynthetic p53 variants.

Main Results:

• Chemically synthesized p53 variants with specific phosphorylation marks (Ser15ph, Ser20ph, Ser15,20ph) were successfully generated and confirmed to be structurally and functionally intact.
• Phosphorylation in the N-terminal domain of p53 was found to enhance p300-dependent acetylation by approximately twofold.
• These findings support the role of N-terminal phosphorylation in p53 activation.

Conclusions:

• The developed protein semi-synthesis approach provides a valuable tool for studying p53 regulation by PTMs.
• Site-specific phosphorylation of p53's N-terminus directly influences its acetylation, a key step in p53 activation.
• This methodology will advance mechanistic understanding of how p53, a critical tumor suppressor, is controlled by diverse posttranslational modifications.