Exploring Potential Binding Modes of Small Drug-like Molecules to the Polo-Box Domain of Human Polo-like Kinase 1.

Purpurogallin (PPG) and Poloxin have been reported as inhibitors of the polo-box domain (PBD) of human polo-like kinase 1 (Plk1). However, our experimental results demonstrated that PPG, but not Poloxin, binds to the phospho-binding pocket of the PBD, suggesting that their modes of PBD inhibition are distinct. Induced fit docking (IFD) analyses led us to propose that PPG fills the SpT pocket via pi-pi stacking and hydrogen bonding interactions, thus providing a rationale for designing novel PBD inhibitors. In contrast, Poloxin may fill a different site present near the SpT pocket by forming a covalent bond with a nucleophilic Cys residue.