Engineering of trypsin and its impact on beta-casein processing

Area of Science:

• Biochemistry
• Enzymology
• Protein Chemistry

Background:

• Tryptic processing of beta-casein generates valuable peptides, but product inhibition by peptide (1-105) limits efficiency.
• Modulating protease activity is crucial for controlling peptide generation and overcoming product inhibition.

Purpose of the Study:

• To engineer trypsin variants with altered substrate specificity by mutating the K188 residue.
• To investigate the impact of aromatic substitutions at position 188 on trypsin's catalytic properties and substrate cleavage patterns.
• To explore the potential of these modified proteases in hydrolyzing resistant protein structures.

Main Methods:

• Site-directed mutagenesis of trypsin at position 188 (K188F, K188Y, K188W).
• Enzymatic activity assays using synthetic substrates and natural substrate beta-casein across a pH range (7-10).
• Kinetic analysis to determine changes in substrate specificity and cleavage sites.

Main Results:

• Mutant trypsins retained specificity for arginyl and lysyl residues but exhibited altered optimal pH.
• Proteolysis of beta-casein by mutants revealed approximately 30 new cleavage sites, including bonds involving asparagine and glutamine.
• Cleavage site alterations correlated with the introduced aromatic residue at position 188.
• Mutants effectively hydrolyzed the inhibitory peptide (1-105).

Conclusions:

• Mutations at K188 significantly alter trypsin's specificity, leading to broader cleavage of beta-casein.
• The engineered mutants demonstrate enhanced ability to hydrolyze the product-inhibitory peptide (1-105).
• These modified proteases hold promise for degrading resistant protein structures, potentially including amyloid formations.