Related Experiment Videos
Reversible binding of peptide aldehydes to papain. Structure-activity relationships
R P Hanzlik1, S P Jacober, J Zygmunt
1Department of Medicinal Chemistry, University of Kansas, Lawrence 66045-2506.
Biochimica Et Biophysica Acta
|January 23, 1991
Summary
Peptide aldehydes and nitriles act as transition-state analogs for papain, binding tightly to the enzyme. This study reveals key interactions in papain
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Aldehydes are known to hydrate in aqueous solutions.
- Papain is a cysteine protease that utilizes a catalytic triad for enzymatic activity.
- Understanding enzyme-inhibitor interactions is crucial for drug design and mechanistic studies.
Purpose of the Study:
- To investigate the hydration and papain binding of peptide and hipuryl aldehydes.
- To determine if aldehydes and nitriles act as similar types of enzyme inhibitors.
- To propose a model for substrate and analog binding to papain.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy was used to measure aldehyde hydration.
- Fluorescence titration was employed to quantify aldehyde binding to papain.
- Dissociation constants (Kd) were calculated for enzyme-adducts.
Main Results:
- Eleven peptide and hipuryl aldehydes were found to be 90-95% hydrated in solution.
- Dehydration of these hydrates was endothermic with a positive entropy.
- N-Ac-L-PheNHCH2CHO exhibited particularly tight binding (Kd,corr = 0.00043 micro M).
- Binding constants for aldehydes strongly correlated with those of analogous nitriles (r = 0.99).
Conclusions:
- Peptide aldehydes and nitriles function as transition-state or reactive intermediate analogs for papain.
- A binding model highlights a covalent interaction with Cys-25 and specific hydrogen bonds and hydrophobic interactions.
- Hippuryl derivatives show limited specificity, reducing their utility in papain studies.