Cucurbit[8]uril Reactivation of an Inactivated Caspase‐8 Mutant Reveals Differentiated Enzymatic Substrate Processing

Caspase‐8 constructs featuring an N‐terminal FGG sequence allow for selective twofold recognition by cucurbit[8]uril, which leads to an increase of the enzymatic activity in a cucurbit[8]uril dose‐dependent manner. This supramolecular switching has enabled for the first time the study of the same caspase‐8 in its two extreme states; as full monomer and as cucurbit[8]uril induced dimer. A mutated, fully monomeric caspase‐8 (D384A), which is enzymatically inactive towards its natural substrate caspase‐3, could be fully reactivated upon addition of cucurbit[8]uril. In its monomeric state caspase‐8 (D384A) still processes a small synthetic substrate, but not the natural caspase‐3 substrate, highlighting the close interplay between protein dimerization and active site rearrangement for substrate selectivity. The ability to switch the caspase‐8 activity by a supramolecular system thus provides a flexible approach to studying the activity of a protein at different oligomerization states.