Pre-Anchoring of Pin1 to Unphosphorylated c-Myc in a Fuzzy Complex Regulates c-Myc Activity

Sara Helander, Meri Montecchio, Robert Pilstål, Yulong Su, Jacob Kuruvilla, Malin Elvén, Javed M.E. Ziauddin, Madhanagopal Anandapadamanaban, Susana Cristobal, Patrik Lundström, Rosalie C. Sears, Björn Wallner, Maria Sunnerhagen

Hierarchic phosphorylation and concomitant Pin1-mediated proline isomerization of the oncoprotein c-Myc controls its cellular stability and activity. However, the molecular basis for Pin1 recognition and catalysis of c-Myc and other multisite, disordered substrates in cell regulation and disease is unclear. By nuclear magnetic resonance, surface plasmon resonance, and molecular modeling, we show that Pin1 subdomains jointly pre-anchor unphosphorylated c-Myc1-88 in the Pin1 interdomain cleft in a disordered, or "fuzzy", complex at the herein named Myc Box 0 (MB0) conserved region N-terminal to the highly conserved Myc Box I (MBI). Ser62 phosphorylation in MBI intensifies previously transient MBI-Pin1 interactions in c-Myc1-88 binding, and increasingly engages Pin1PPIase and its catalytic region with maintained MB0 interactions. In cellular assays, MB0 mutated c-Myc shows decreased Pin1 interaction, increased protein half-life, but lowered rates of Myc-driven transcription and cell proliferation. We propose that dynamic Pin1 recognition of MB0 contributes to the regulation of c-Myc activity in cells.