Application of oxime-diversification to optimize ligand interactions within a cryptic pocket of the polo-like kinase 1 polo-box domain

Authors

• XZ Zhao
• D Hymel
• TR Burke

Abstract

Members of the polo-like kinase (Plk) family of serine/threonine protein kinases play crucial roles in cell cycle regulation and proliferation. Of five Plks (Plk1 – 5), Plk1 is recognized as an anticancer drug target. Plk1 contains multiple structural components that are important for its proper biological function. These include an N-terminal catalytic domain and a C-terminal non-catalytic polo-box domain (PBD). The PBD binds to phosphothreonine (pT) and phosphoserine (pS)-containing sequences. Blocking PBD-dependent interactions offers a potential means of down-regulating Plk1 function that is distinct from targeting its ATP-binding site. Oxime-based post-solid phase diversification is a form of directed fragment screening, which can be highly effective in optimizing protein-ligand interactions. As one example, starting from the known PBD-binding peptide “PLHSpT,” we have previously used this approach to identify a hydrophobic cryptic binding pocket on the surface of the PBD, whose access can enhance peptide-binding affinity by approximately 1000-fold. As reported herein, we have employed this technology to further extend and optimize PBD-ligand interactions. By a process involving initial screening of a set of 87 aldehydes using an oxime ligation-based strategy, we were able to achieve a several-fold affinity enhancement over one of the most potent previously known Plk1 PBD-binding inhibitors. This improved binding may result from accessing a newly identified auxiliary region proximal to a key hydrophobic cryptic pocket on the surface of the protein. We have also shown that selectivity for the Plk1 PBD relative to the PBDs of Plk2 and Plk3 can be significantly enhanced by modulating interactions within this region. Our findings could have general applicability to the design of Plk1 PBD-binding antagonists.

Scientific Focus Area: Chemical Biology

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