Pyk2 tyrosine kinase conformations probed by molecular imprinted nanoparticles

Abstract

Proline-rich tyrosine kinase 2 (PYK2) and focal adhesion kinase (FAK) encompass a subfamily of nonreceptor tyrosine kinases. Whereas FAK is activated by clustering at focal adhesion membranes, PYK2 can be activated Ca2+-flux. Nevertheless, both kinases share some activation mechanistic details. The release of a FERM domain-mediated autoinhibitory conformation leads to autophosphorylation of a tyrosine located in the FERM-kinase linker. The phosphorylated tyrosine forms a docking site for Src kinase which contributes to full activation. While the conformation of the PYK2 autophosphorylation site remains unknown, the structure of the FAK FERM−kinase revealed that the corresponding regulatory site is sequestered in an abbreviated β sheet. We have recently reported that peptide-binding molecular imprinted nanoparticles (MINPs) targeting the consensus PYK2 phosphorylation site (Y402) and surroundings are able to inhibit autophosphorylation. However, the degree of inhibition was highly influenced by the putative conformation of the target binding site. We sought to further explore the association of MINP target conformational accessibility and inhibitor potency. In vitro kinase assays of PYK2 FERM-kinase indicate the ability of MINPs to inhibit the autophosphorylation of Y402. MINPs were designed to bind three distinct regions of the linker sequence. Autophosphorylation inhibition was highly dependent on linker region. Interestingly, the MINP impinging directly on the Y402 site exhibited the weakest inhibition among the three MINPs tested. The differential impact between linker target sites suggests that the PYK2 Y402 autophosphorylation site may also be constrained via secondary structure in the autoinhibited conformation. Taken together, we validate that MINPs can serve as inhibitors of protein kinase phosphorylation. We continue to explore the intriguing possibility that MINPs can serve as conformational probes.