Design of synthetic gene libraries encoding random sequence proteins with desired ensemble characteristics

Area of Science:

• Biochemistry and Molecular Biology
• Synthetic Biology
• Bioinformatics

Background:

• Random sequence polypeptide libraries are valuable for discovering novel proteins, ligands, and therapeutic leads.
• Previous methods using equimolar nucleotide mixtures had limitations in controlling codon composition and avoiding termination codons.
• Complex designs are needed for random polypeptide libraries to meet specific requirements for applications like vaccine and therapeutic development.

Purpose of the Study:

• To design nucleotide mixtures for synthesizing semirandom DNA that encodes random sequence polypeptides with desired ensemble characteristics.
• To develop a method that minimizes termination codons and matches target amino acid compositions.
• To create a versatile tool for constructing high-diversity random polypeptide libraries.

Main Methods:

• Designed three nucleotide mixtures corresponding to the three codon positions.
• Synthesized semirandom DNA using repeated cycles of these designed nucleotide mixtures.
• Employed a spreadsheet and a refining grid search algorithm to determine optimal nucleotide ratios.
• Set design targets of less than or equal to 1% stop codons and amino acid composition based on natural globular proteins.

Main Results:

• Achieved similar nucleotide ratios using both manual spreadsheet design and algorithmic grid search.
• Successfully created semirandom DNA with a designed three-residue repeat pattern.
• Demonstrated the ability to encode random sequence polypeptides with controlled ensemble characteristics.
• Minimized the occurrence of termination codons to meet design targets.

Conclusions:

• Semirandom DNA synthesized with a designed, three-residue repeat pattern is a powerful tool for constructing highly diverse random polypeptide libraries.
• The developed nucleotide mixture design strategy effectively controls polypeptide composition and reduces stop codon frequency.
• This method advances the creation of libraries for discovering novel ligands, vaccines, and therapeutics.