Structural and kinetic evidence of aging after organophosphate inhibition of human Cathepsin A

• Published in: Biochemical pharmacology 2020-07, Vol.177, p.113980-113980, Article 113980
• Main Authors: Bouknight, Kayla D., Jurkouich, Kayla M., Compton, Jaimee R., Khavrutskii, Ilja V., Guelta, Mark A., Harvey, Steven P., Legler, Patricia M.
• Format: Article
• Language: English
• Subjects: Aging; Cathepsin A; Cholinesterase; Inhibition; Organophosphate
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/j.bcp.2020.113980

[Display omitted] Human Cathepsin A (CatA) is a lysosomal serine carboxypeptidase of the renin-angiotensin system (RAS) and is structurally similar to acetylcholinesterase (AChE). CatA can remove the C-terminal amino acids of endothelin I, angiotensin I, Substance P, oxytocin, and bradykinin, and can deamidate neurokinin A. Proteomic studies identified CatA and its homologue, SCPEP1, as potential targets of organophosphates (OP). CatA could be stably inhibited by low µM to high nM concentrations of racemic sarin (GB), soman (GD), cyclosarin (GF), VX, and VR within minutes to hours at pH 7. Cyclosarin was the most potent with a kinetically measured dissociation constant (KI) of 2 µM followed by VR (KI = 2.8 µM). Bimolecular rate constants for inhibition by cyclosarin and VR were 1.3 × 103 M−1sec−1 and 1.2 × 103 M−1sec−1, respectively, and were approximately 3-orders of magnitude lower than those of human AChE indicating slower reactivity. Notably, both AChE and CatA bound diisopropylfluorophosphate (DFP) comparably and had KIDFP = 13 µM and 11 µM, respectively. At low pH, greater than 85% of the enzyme spontaneously reactivated after OP inhibition, conditions under which OP-adducts of cholinesterases irreversibly age. At pH 6.5 CatA remained stably inhibited by GB and GF and