Date of Award
Doctor of Philosophy (PhD)
Jeanne A. Hardy
Vincent M. Rotello
Craig T. Martin
Alzheimer's Disease, apoptosis, Cancer, caspase, Huntington's Disease
Caspases are cysteine proteases best known for their controlling roles in apoptosis and inflammation. Caspase-6 has recently been shown to play a key role in the cleavage of neurodegenerative substrates that causes Huntington and Alzheimer's Disease, heightening interest in caspase-6 and making it a drug target. All thirteen human caspases have related specificities for binding and cleaving substrate, so achieving caspase-specific regulation at the active site has been extremely challenging if not impossible. We have determined the structures of four unliganded forms of caspase-6, which attain a novel helical structure not observed in any other caspases. In this conformation, rotation of the 90's helix results in formation of a cavity that can function as an allosteric site, locking caspase-6 into an inactive conformation. We are using this cavity to look for chemical ligands that target this cavity and maintain caspase-6 in the inactive, helical conformation. We found that known allosteric inhibitors of caspase-3 and -7 also inhibit caspase-6 through a cavity at the dimer interface. We have determined new structures of a phosphomimetic state and a zinc-bound conformation of caspase-6, which show the molecular details of two additional allosteric sites. The phosphomimetic form of caspase-6 inactivates caspase-6 by disrupting formation of the substrate binding-groove by steric clash of the phosphorylated residue with P201 in the L2' loop. Another allosteric site was found on the "back" of caspase-6 that coordinates a zinc molecule that leads to inactivation. In total we have uncovered four independent allosteric sites in caspase-6, structurally characterized inhibition from these sites and demonstrated that each of these sites might be targeted for caspase-6 specific inhibition by synthetic or natural-product ligands.
Velazquez-Delgado, Elih M., "Allosteric Regulation of Caspase-6 Proteolytic Activity" (2012). Open Access Dissertations. Paper 630.