Protein kinases are central players in the regulation of cell cycle and signalling pathways. Their catalytic activities are strictly regulated through post‐translational modifications and protein–protein interactions that control switching between inactive and active states. These states have been studied extensively using protein crystallography, although the dynamic nature of protein kinases makes it difficult to capture all relevant states. Here, we describe two recent structures of Aurora‐A kinase that trap its active and inactive states. In both cases, Aurora‐A is trapped through interaction with a synthetic protein, either a single‐domain antibody that inhibits the kinase or a hydrocarbon‐stapled peptide that activates the kinase. These structures show how the distinct synthetic proteins target the same allosteric pocket with opposing effects on activity. These studies pave the way for the development of tools to probe these allosteric mechanisms in cells.