Structure-based chimeric enzymes as an alternative to directed enzyme evolution: phytase as a test case.

Area of Science:

• Enzymology
• Protein Engineering
• Biotechnology

Background:

• Thermostability is a critical attribute for commercial fungal phytase enzymes.
• Previous attempts to enhance Aspergillus terreus phytase thermostability by restoring surface ionic interactions and hydrogen bonds were ineffective.
• Homologous phytase from Aspergillus niger exhibits higher thermostability.

Purpose of the Study:

• To engineer a more thermostable variant of Aspergillus terreus phytase.
• To investigate the impact of replacing secondary structure elements on enzyme stability and activity.
• To explore structure-based chimeric enzyme design as a method for enzyme improvement.

Main Methods:

• Site-directed mutagenesis to restore surface interactions.
• Replacement of an alpha-helix in Aspergillus terreus phytase with the corresponding A. niger phytase sequence, guided by crystal structure.
• Enzymatic activity and thermostability assays.

Main Results:

• Mutations restoring surface interactions did not improve thermostability.
• Replacement of an alpha-helix with the homologous A. niger sequence yielded a hybrid enzyme with significantly improved thermostability.
• The engineered enzyme retained its original enzymatic activity.
• The thermostability of the hybrid enzyme approached that of the more stable A. niger phytase, despite incorporating only a small segment.

Conclusions:

• Structure-based design of chimeric enzymes is effective for enhancing phytase thermostability.
• Replacing specific structural elements can confer significant stability improvements.
• This approach offers a viable alternative to directed evolution, especially when large-scale screening is challenging.