Let it bind: cyclization of Mig-6 segment 2 to target EGFR signaling in lung cancer

Activation of epidermal growth factor receptor signaling by kinase dimerization plays a crucial role in the development, progression, and metastasis of lung cancer. Tumor suppressor Mig-6 is a natural inhibitory protein of epidermal growth factor receptor signaling; the protein uses its two regions, namely segments 1 and 2, to directly interact with kinase dimerization interface and then inactivates the kinases. Here, we attempted to improve the binding capability of isolated segment 2 peptide to epidermal growth factor receptor family kinases by cyclizing the peptide. In the procedure, a disulfide bond was introduced across two ends of the peptide to constrain the peptide conformation in an antiparallel, double-stranded β-sheet. Molecular dynamics simulations indicated high-structural flexibility and intrinsic disorder associated with the linear peptide of Mig-6 segment 2, whereas its cyclized version exhibited a considerable rigidity and low mobility. Molecular mechanics/Poisson–Boltzmann surface area calculations and quasiharmonic analysis revealed that the cyclization influences kinase–peptide interaction enthalpy modestly, but can largely minimize entropy penalty upon the interaction, thus effectively restoring peptide binding free energy. Fluorescence polarization assays found no affinity of linear peptide to epidermal growth factor receptor family kinases, while a weak or moderate affinity can be observed for cyclic peptide binding to the kinases.