Synergistic binding of the phosphorylated S233- and S259-binding sites of C-RAF to one 14-3-3zeta dimerMolzan, M., Ottmann, C.
(2012) J Mol Biol 423: 486-495
- PubMed: 22922483
- DOI: https://doi.org/10.1016/j.jmb.2012.08.009
- Primary Citation of Related Structures:
- PubMed Abstract:
C-RAF kinase is a central component of the Ras-RAF-MEK (mitogen-activated protein kinase/extracellular signal-regulated kinase)-ERK (extracellular signal-regulated kinase) pathway, which has been shown to be activated in 30% of human tumors. 14-3-3 proteins inactivate C-RAF by binding to the two N-terminal phosphorylation-dependent binding sites surrounding S233 and S259. 14-3-3 proteins can bind two target sequences located on one polypeptide chain simultaneously, thereby increasing binding affinity compared to single-site binding and possibly allowing regulated 14-3-3 binding through gatekeeper phosphorylation. To date, it was unclear whether 14-3-3 proteins can bind the two N-terminal phosphorylation-dependent binding sites of C-RAF simultaneously. Fluorescence polarization using phosphorylated peptides demonstrated that S233 is the low-affinity and S259 is the high-affinity binding site, while simultaneous engagement of both sites by 14-3-3ζ enhances affinity compared to single-site binding. Determination of a 1:1 stoichiometry for the di-phosphorylated peptide binding to one 14-3-3ζ dimer with isothermal titration calorimetry was supported by the crystal structure of the 14-3-3ζ/C-RAFpS233,pS259 complex. Cellular localization studies validate the significance of these sites for cytoplasmic retention of C-RAF, suggesting an extended mechanism of RAF regulation by 14-3-3 proteins.
Chemical Genomics Centre of the Max-Planck-Society, Otto-Hahn-Strasse 15, 44227 Dortmund, Germany.