title: Cocrystal structures of primed side-extending alpha-ketoamide inhibitors reveal novel calpain-inhibitor aromatic interactions.
abstract: Calpains are intracellular cysteine proteases that catalyze the cleavage of target proteins in response to Ca(2+) signaling. When Ca(2+) homeostasis is disrupted, calpain overactivation causes unregulated proteolysis, which can contribute to diseases such as postischemic injury and cataract formation. Potent calpain inhibitors exist, but of these many cross-react with other cysteine proteases and will need modification to specifically target calpain. Here, we present crystal structures of rat calpain 1 protease core (muI-II) bound to two alpha-ketoamide-based calpain inhibitors containing adenyl and piperazyl primed-side extensions. An unexpected aromatic-stacking interaction is observed between the primed-side adenine moiety and the Trp298 side chain. This interaction increased the potency of the inhibitor toward muI-II and heterodimeric m-calpain. Moreover, stacking orients the adenine such that it can be used as a scaffold for designing novel primed-side address regions, which could be incorporated into future inhibitors to enhance their calpain specificity.
authors.affiliation: Department of Biochemistry, Queen's University, Kingston, Ontario, K7L 3N6, Canada.
authors.forename: Jin
authors.initials: J
authors.lastname: Qian
authors.forename: Dominic
authors.initials: D
authors.lastname: Cuerrier
authors.forename: Peter L
authors.initials: PL
authors.lastname: Davies
authors.forename: Zhaozhao
authors.initials: Z
authors.lastname: Li
authors.forename: James C
authors.initials: JC
authors.lastname: Powers
authors.forename: Robert L
authors.initials: RL
authors.lastname: Campbell
mesh_terms: D024322:Amino Acids, Aromatic / Q000737:chemistry; D000818:Animals; D002154:Calpain / Q000037:antagonists & inhibitors / Q000737:chemistry*; D002219:Carbamates / Q000037:antagonists & inhibitors*; D018360:Crystallography, X-Ray; D004151:Dipeptides / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000494:pharmacology; D006023:Glycoproteins / Q000737:chemistry*; D011487:Protein Conformation; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D024322:Amino Acids, Aromatic; D002219:Carbamates; D004151:Dipeptides; D006023:Glycoproteins; C039304:calpain inhibitors; D002154:Calpain