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End binding protein 1 (EB1) is a key element in the complex network of protein-protein interactions at microtubule growing ends which has a fundamental role in microtubule polymerisation. EB1 regulates the microtubule dynamic behaviour, through protein recruitment, and has been associated with several disease states, such as cancer and neuronal diseases. Diverse EB1 binding partners are recognised through a conserved SxIP motif within an intrinsically disordered region enriched with basic, serine and proline residues. Crystal structure of EB1 in complex with a peptide containing the SxIP motif demonstrated that the isoleucine-proline dipeptide is bound into a well‐defined cavity of EB1 that may be suitable for small molecule targeting. The research described herein reports the use of a multidisciplinary approach for the discovery of the first small molecule scaffold to target the EB1 recruiting domain. This approach included virtual screening (structure and ligand based design) and multiparameter compound selection. Solution NMR structures of the C-terminal domain of EB1 in the free form and in complex with the small molecule are also reported. A key finding from these structures is that the hydrophobic binding pocket reported to be essential for recruiting SxIP proteins is not pre-formed but highly dynamic in solution. This brings new insights to the protein recruitment mechanism regulated by EB1 and for the identification of new small molecule inhibitors for the EB1-SxIP protein interactions. The interaction of short length peptides containing the SxIP motif with EB1 was characterised through the use of solution NMR and ITC methods. The contributions for the binding of the SxIP motif and neighbouring residues to EB1 were quantified in terms of binding energy. A structural model shows that the binding pocket of EB1 is largely extended when in complex. This research describes not only the first chemical scaffold that targets EB1, it details important structural features of the interaction of this protein with SxIP containing peptides. This structural information provides fundamental understanding of this interaction that can be exploited in the future to discover higher affinity ligands. |
