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.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:open_access_dissertations-1631 |
| Date | 01 September 2012 |
| Creators | Velazquez-Delgado, Elih M. |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Open Access Dissertations |
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