Quantifying tetrahedral adduct formation and stabilization in the cysteine and the serine proteases

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Title: Quantifying tetrahedral adduct formation and stabilization in the cysteine and the serine proteases
Authors: Cleary, Jennifer A.
Doherty, William
Evans, Paul
Malthouse, J.Paul G.
Permanent link: http://hdl.handle.net/10197/6746
Date: Oct-2015
Abstract: Two new papain inhibitors have been synthesized where the terminal α-carboxyl groups of Z-Phe-Ala-COOH and Ac-Phe-Gly-COOH have been replaced by a proton to give Z-Phe-Ala-H and Ac-Phe-Gly-H. We show that for papain, replacing the terminal carboxylate group of a peptide inhibitor with a hydrogen atom decreases binding 3–4 fold while replacing an aldehyde or glyoxal group with a hydrogen atom decreases binding by 300,000–1,000,000 fold. Thiohemiacetal formation by papain with aldehyde or glyoxal inhibitors is shown to be ~ 10,000 times more effective than hemiacetal or hemiketal formation with chymotrypsin. It is shown using effective molarities, that for papain, thiohemiacetal stabilization is more effective with aldehyde inhibitors than with glyoxal inhibitors. The effective molarity obtained when papain is inhibited by an aldehyde inhibitor is similar to the effective molarity obtained when chymotrypsin is inhibited by glyoxal inhibitors showing that both enzymes can stabilize tetrahedral adducts by similar amounts. Therefore the greater potency of aldehyde and glyoxal inhibitors with papain is not due to greater thiohemiacetal stabilization by papain compared to the hemiketal and hemiacetal stabilization by chymotrypsin, instead it reflects the greater intrinsic reactivity of the catalytic thiol group of papain compared to the catalytic hydroxyl group of chymotrypsin. It is argued that while the hemiacetals and thiohemiacetals formed with the serine and cysteine proteases respectively can mimic the catalytic tetrahedral intermediate they are also analogues of the productive and non-productive acyl intermediates that can be formed with the cysteine and serine proteases.
Funding Details: Irish Research Council
University College Dublin
Type of material: Journal Article
Publisher: Elsevier
Copyright (published version): 2015 Elsevier
Keywords: Aldehyde inhibitorGlyoxal inhibitorTetrahedral intermediateCysteine proteaseSerine protease
DOI: 10.1016/j.bbapap.2015.07.006
Language: en
Status of Item: Peer reviewed
Appears in Collections:Conway Institute Research Collection
Biomolecular and Biomedical Science Research Collection
CSCB Research Collection
Chemistry Research Collection

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