title: Caspase-7 uses an exosite to promote poly(ADP ribose) polymerase 1 proteolysis.
abstract: During apoptosis, hundreds of proteins are cleaved by caspases, most of them by the executioner caspase-3. However, caspase-7, which shares the same substrate primary sequence preference as caspase-3, is better at cleaving poly(ADP ribose) polymerase 1 (PARP) and Hsp90 cochaperone p23, despite a lower intrinsic activity. Here, we identified key lysine residues (K(38)KKK) within the N-terminal domain of caspase-7 as critical elements for the efficient proteolysis of these two substrates. Caspase-7's N-terminal domain binds PARP and improves its cleavage by a chimeric caspase-3 by ∼30-fold. Cellular expression of caspase-7 lacking the critical lysine residues resulted in less-efficient PARP and p23 cleavage compared with cells expressing the wild-type peptidase. We further showed, using a series of caspase chimeras, the positioning of p23 on the enzyme providing us with a mechanistic insight into the binding of the exosite. In summary, we have uncovered a role for the N-terminal domain (NTD) and the N-terminal peptide of caspase-7 in promoting key substrate proteolysis.
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Health Sciences, Institut de Pharmacologie de Sherbrooke,  Université de Sherbrooke, Sherbrooke, QC,  Canada J1H 5N4.
authors.forename: Dave
authors.initials: D
authors.lastname: Boucher
authors.forename: Véronique
authors.initials: V
authors.lastname: Blais
authors.forename: Jean-Bernard
authors.initials: JB
authors.lastname: Denault
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000737:chemistry* / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D019746:Intramolecular Oxidoreductases / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D000071876:Prostaglandin-E Synthases; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3; D053179:Caspase 7; D019746:Intramolecular Oxidoreductases; D000071876:Prostaglandin-E Synthases