Calcium and integrin binding protein 1 (CIB1) is an EF-hand-containing, small intracellular protein that has recently been implicated in cancer cell survival and proliferation. In particular, CIB1 depletion significantly impairs tumor growth in triple-negative breast cancer (TNBC). Thus, CIB1 is a potentially attractive target for cancer chemotherapy that has yet to be validated by a chemical probe. To produce a probe molecule to the CIB1 helix 10 (H10) pocket and demonstrate that it is a viable target for molecular intervention, the researchers employed random peptide phage display to screen and select CIB1-binding peptides. The top peptide sequence selected, UNC10245092, was produced synthetically, and binding to CIB1 was confirmed by isothermal titration calorimetry (ITC) and a time-resolved fluorescence resonance energy transfer (TR-FRET) assay. Both assays showed that the peptide bound to CIB1 with low nanomolar affinity. CIB1 was cocrystallized with UNC10245092, and the 2.1 Å resolution structure revealed that the peptide binds as an α-helix in the H10 pocket, displacing the CIB1 C-terminal H10 helix and causing conformational changes in H7 and H8. UNC10245092 was further derivatized with a C-terminal Tat-derived cell penetrating peptide (CPP) to demonstrate its effects on TNBC cells in culture, which are consistent with results of CIB1 depletion. These studies provide a first-in-class chemical tool for CIB1 inhibition in cell culture and validate the CIB1 H10 pocket for future probe and drug discovery efforts.

Title:
Discovery and Characterization of Peptide Inhibitors for Calcium and Integrin Binding Protein 1
Authors:
Ana C. Puhl, Jonathan W. Bogart, Victoria A. Haberman, Jacob E. Larson, Andre S. Godoy, Jacqueline L. Norris-Drouin, Stephanie H. Cholensky, Tina M. Leisner, Stephen V. Frye, Leslie V. Parise, Albert A. Bowers, and Kenneth H. Pearce
Citation:
ACS Chemical Biology 2020 15 (6), 1505-1516
URL:
https://pubs.acs.org/doi/10.1021/acschembio.0c00144?ref=pdf