Quest for a turnover mechanism in peptide-based enzyme mimics

• Nine peptide enzyme mimics were designed and tested for acetylation/deacylation.
• Peptides with Phe-Cys-Phe-His had significantly higher acetyl group transfer rates.
• Peptide backbone bending due to Phe brings Cys and His into closer proximity.
• NMR results support closer proximity of Cys and His in peptides with Phe.
• Lower Cys thiol pKa supports closer proximity of Cys and His in peptides with Phe.

Creation of synthetic structures with an enzyme-like mechanism and turnover remains a significant challenge. In this study, peptides containing a cysteine thiol and histidine imidazole group were designed to mimic the active site of the cysteine protease papain. Ellman's reagent trapping experiments showed that rapid acetyl group exchange exists between the thiol and imidazole groups. This exchange rate increased significantly in peptides with bulky R-groups (phenylalanine) between the cysteine and histidine. A reduction of the cysteine thiol pKa and NMR results further supports closer proximity of the thiol and imidazole groups in peptides with faster acetyl group exchange.

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