Variants of subtilisin BPN' with altered specificity profiles

Area of Science:

• Enzymology
• Protein Engineering
• Biocatalysis

Background:

• Subtilisin BPN' is a serine protease with broad substrate specificity.
• Improving enzyme specificity is crucial for targeted biocatalytic applications.
• The S4 binding pocket influences substrate recognition, particularly for hydrophobic side chains.

Purpose of the Study:

• To enhance the specificity of subtilisin BPN' for substrates with large hydrophobic P4 side chains.
• To investigate the effects of single and double amino acid substitutions in the S4 pocket on enzyme kinetics and specificity.
• To explore strategies for designing highly specific protease variants.

Main Methods:

• Site-directed mutagenesis was employed to introduce amino acid replacements at positions 104, 107, and 126.
• Kinetic parameters (kcat/KM) were measured to assess substrate specificity.
• Analysis of single and double mutants to understand the additive or non-additive effects of mutations.

Main Results:

• Single mutations I107G and Y104A significantly increased specificity for certain hydrophobic residues.
• L126A substitution enhanced catalytic efficiency for isoleucine 28-fold.
• The double mutant I107G/L126V exhibited the largest specificity improvement (340-fold for leucine vs. alanine), but effects were not additive.
• The I107G/Y104A double mutant showed impaired specificity compared to single mutants.

Conclusions:

• Engineering the S4 pocket can improve subtilisin specificity, but the effects of combined mutations are complex and not always additive.
• Designing highly specific protease variants requires careful consideration of interacting mutations.
• The study highlights the non-trivial nature of combining mutations for precise enzyme engineering.