title: Development of a specific inhibitor for the placental protease, cathepsin P.
abstract: Gene duplications in rodents have given rise to a family of proteases that are expressed exclusively in placenta. To define the biological role of these enzymes specific inhibitors are needed to differentiate their activities from other more ubiquitously expressed proteases, such as cathepsins B and L. Libraries of peptidyl inhibitors based upon a 4-cyclohexanone pharmacophore were screened for inhibition of cathepsins P, L, and B. The tightest binding dipeptidyl inhibitor for cathepsin P contained Tyr in P(2) and Trp in P(2)('), consistent with the specificity of this enzyme for hydrophobic amino acids at these sites in synthetic substrates. An inhibitor containing Trp in both P(2) and P(2)(') provided better discrimination between cathepsin P and cathepsins B and L. Extension of the inhibitors to include P(3), and P(3)(') amino acids identified an inhibitor with Trp in P(2), P(2)('), and P(3), and Phe in P(3)(') that bound to cathepsin P with a K(i) of 32 nM. This specificity for inhibitors with hydrophobic aromatic amino acids in these four positions is unique among the lysosomal cysteine proteases. This inhibitor bound to cathepsin P an order of magnitude tighter than to mouse and human cathepsin L and two orders of magnitude tighter than to human cathepsin B. Cbz-Trp-Trp-4-cyclohexanone-Trp-Phe-OMe can discriminate cathepsin P from cathepsins B and L and consequently can be used to specifically inhibit and identify cathepsin P in cellular systems.
authors.affiliation: Department of Biomedical Research, Alfred I duPont Hospital for Children, 1600 Rockland Road, Wilmington, DE 19803, USA.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Hassanein
authors.forename: Fengtian
authors.initials: F
authors.lastname: Xue
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Seto
authors.forename: Robert W
authors.initials: RW
authors.lastname: Mason
mesh_terms: D000818:Animals; D056657:Cathepsin K; D002403:Cathepsins / Q000037:antagonists & inhibitors*; D015195:Drug Design; D005260:Female; D051379:Mice; D010920:Placenta / Q000196:embryology*; D011480:Protease Inhibitors / Q000138:chemical synthesis*
chemical_list: D011480:Protease Inhibitors; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K; C534132:Ctsk protein, mouse