Herein we have described a rational approach to the development of competitive peptidomimetic inhibitors, e.g. TACC3518-532-L/R-Bph-I/fP, of the TACC3/Aurora-A interaction. Key to the success of this approach was the incorporation of a constraint within the peptide despite the absence of a welldefined secondary structure at the interface. Whilst a structurally well-defined interaction between TACC3/Aurora-A occurs and must be replicated in large part by the peptidomimetic, the unbound form of both the peptide and the constrained peptidomimetic were shown to be largely disordered. The enhanced affinity of the constrained peptidomimetic arises from a restricted conformational space, in effect raising the energy of the ensemble and resulting in a more favourable entropy of binding to the kinase (Fig. ). This behavior is similar to that recently described to occur upon methylation of backbone amides for a ligand that recognizes its target through β-strand complementation. Raising the energy of the unbound ensemble can offer a general route to enhancing target binding affinity as opposed to preorganizing a ligand in its bound conformation -a difficult prospect given PPIs occur as partially bound states. Promisingly, the high affinity of the most potent peptidomimetic TACC3518-532-L/R-Bph-I/fP opens up new opportunities to understand and allosterically regulate the function and interactions of Aurora-A. A number of Aurora-A interactors e.g. TACC3 26 and TPX2 53 activate the kinase, despite binding at different sites, whilst paradoxically CEP192, which binds at both TACC3 and TPX2 sites, suppresses kinase activity. All three proteins may participate in additional non-covalent interaction with the kinase beyond that revealed by their x-ray structures, complicating an interpretation of the minimal determinants for allosteric kinase modulation. In contrast our minimal peptidomimetics of only thirteen residues are sufficient to induce conformational changes needed to activate the kinase by binding only a single pocket on the N-lobe. This minimal interaction is also sufficient to allosterically displace N-Myc from its binding site. Inhibition of the Aurora-A/N-Myc interaction 39 may represent a target for anticancer drugdevelopment -a number of active-site ligands have been shown to allosterically displace N-Myc, but may prove problematic as a consequence of downregulating the essential functions of Aurora-A. Being able to knock out the TACC3/Aurora-A interaction without inhibiting kinase activity may thus represent a promising alternative to these active-site ligands. Thus, these peptidomimetic tools inform on allosteric regulation in Aurora A and reveal new opportunities for chemical probe development.