Exploring nonnatural evolutionary pathways by saturation mutagenesis: rapid improvement of protein function

Area of Science:

• Protein engineering
• Biochemistry
• Molecular biology

Background:

• Random point mutagenesis is limited in exploring protein sequence space, particularly for nonconservative amino acid substitutions.
• The impact of this limitation on directed evolution and protein trait improvement is not fully understood.

Purpose of the Study:

• To investigate the potential of saturation mutagenesis in accessing novel protein sequences for enhanced thermostability.
• To compare the effectiveness of saturation mutagenesis against random point mutagenesis for protein improvement.

Main Methods:

• Random point mutagenesis was applied to the psychrophilic protease subtilisin S41 gene.
• Residues Lys211 and Arg212, identified via point mutagenesis, were subjected to saturation mutagenesis.
• DNA sequencing was used to analyze the amino acid substitutions in the most stable variants.

Main Results:

• Mutations at Lys211 and Arg212 significantly increased subtilisin S41 thermostability.
• Saturation mutagenesis yielded variants with superior stability compared to those from point mutagenesis.
• The most stable variants featured highly hydrophobic residues (e.g., Pro/Ala, Leu/Val) resulting from multiple base substitutions.

Conclusions:

• Saturation mutagenesis effectively explores nonnatural evolution pathways, accessing rare amino acid substitutions.
• This approach enables rapid and significant improvement of protein traits, such as thermostability.
• Saturation mutagenesis is a valuable tool for directed evolution, overcoming limitations of random point mutagenesis.