Kinetic specificity in papain-catalysed hydrolyses.

Area of Science:

• Enzymology
• Protein Chemistry
• Biochemistry

Background:

• Papain is a cysteine protease known for its broad substrate specificity.
• Understanding papain's specificity is crucial for its applications in biotechnology and medicine.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying papain's substrate specificity.
• To propose models for the enzyme-substrate complex and acyl-enzyme intermediate.

Main Methods:

• Analysis of enzyme-substrate interactions.
• Modeling of enzyme-substrate and acyl-enzyme complexes.
• Investigating the role of specific amino acid residues (e.g., glycine-66, aspartic acid-158) in substrate binding.

Main Results:

• Papain's specificity is primarily determined by the formation of the acyl-enzyme intermediate.
• A proposed model suggests substrate binding in the enzyme's cleft, involving specific amino acid residues.
• Cooperative interactions between protein distortion and substrate binding enhance specificity for hydrophobic amino acids like L-phenylalanine.

Conclusions:

• Papain's unique binding mechanism amplifies specificity for hydrophobic residues.
• A conformational relaxation occurs during the transition from enzyme-substrate complex to acyl-enzyme intermediate.
• The findings provide insights into protease mechanism and enzyme engineering.