Fmoc-based chemical synthesis and selective binding to supercoiled DNA of the p53 C-terminal segment and its phosphorylated and acetylated derivatives.

The C-terminal domain of p53 comprises a linker, the tetramerization domain and the regulatory domain, and contains at least seven sites of potential post-translational modification. An improved strategy was developed for the synthesis of large peptides that contain phosphorylated amino acids and p53(303-393), a 91-amino acid peptide, and three post-translationally modified derivatives were synthesized through the sequential condensation of three partially protected segments. Peptide thiolesters were prepared using the sulfonamide-based 'safety-catch' resin approach and employing Fmoc-based solid-phase peptide synthesis. At the N-terminus of the middle building block, a photolabile protecting group, 3,4-dimethoxy-6-nitrobenzyloxycarbonyl, was incorporated to differentiate the N-terminal amino group from the side-chain amino groups. Two sequential couplings were accomplished following this protection strategy. The synthetic products, p53(303-393) and its phosphorylated or acetylated derivatives, exhibited the ability to bind specifically to supercoiled DNA, which is one of the characteristics of this domain.