Downsizing Proto-oncogene cFos to Short Helix-Constrained Peptides That Bind Jun

The oricogenic transcription factor activator protein-I (APE-1) is a DNA-binding protein that Assembles through of Fos and Jun protein subunits, their leuCine-rich helical se'quleriCeS entwining into a coiled coil structure. This study reports doWnsizingz the proto- oncogene cFos protein (380 residues) to shorter pCpticies (37-15 residues) Modified 1,4fitb helix-induCing constraints enhance 'binding to Jun. A crystal structure is reported for a 37-residue FoS-derived peptide (EbsW) bound to jun. This guided iterative downsizing of FosW to shorter peptide sequences that were constrained into stable water-soluble alpha- helices by connecting amino acid side, Chains to foal) cyclic pentapeptide components Strtictural integrity in the presence 'and absence of Jun was assessed by zireular dichroism spectroscopy, while the therinOdynamies of binding, to & US was Measured by isothermal titratibn calorimetry. A 254tesidue constrained peptide one-third shorter yet 25% More helical thanthe structurally characterized 37-reSidue Fos-derived peptide retained 80% of the hinding free energy as a result preorganization in a JIM. binding helix conformation, with.the entropy gain (T Delta S = +3.2 kcal/mol).compensating for the enthalpy loss Attaching penetrating peptide (TAT(48-57)) and a nuclear oCalilation signal (SV40) promoted cell uptake loCalization to the nucleus, and inhibition of the proliferation bf two breast cancer cell lines.