Structural and functional analyses of minimal phosphopeptides targeting the polo-box domain of polo-like kinase 1

Plk1 plays a pivotal role in cell proliferation and is considered an attractive target for anti-cancer therapy. The noncatalytic polo-box domain (PBD) of Plk1 forms a phosphoepitope-binding module for protein-protein interaction. Here, we report the identification of minimal phosphopeptides that specifically interacted with the PBD of Plk1, but not the two closely-related Plk2 and Plk3. Comparative binding studies and analyses of crystal structures of the Plk1 PBD in complex with the minimal phosphopeptides revealed that the C-terminal SpT dipeptide functions as a high affinity anchor, whereas the N-terminal residues are critical for providing both specificity and affinity to the interaction. Inhibition of the Plk1 PBD by phospho-Thr mimetic peptides was sufficient to induce mitotic arrest and apoptotic cell death. Thus, the mode of the minimal peptide and PBD interaction may provide a template for designing anti-Plk1 therapeutic agents.