Standardizing cassette-based deep mutagenesis by Golden Gate assembly

Area of Science:

• Molecular Biology
• Synthetic Biology
• Protein Engineering

Background:

• Existing methods for constructing large, mutagenized protein-encoding libraries using Golden Gate assembly are often system-specific and lack standardization.
• This limits the broad applicability and scalability of generating diverse protein variants for research and development.

Purpose of the Study:

• To present a standardized Golden Gate assembly method for building user-defined, deeply mutagenized protein-encoding libraries.
• To demonstrate the scalability and efficiency of this method for generating a high number of unique protein variants.

Main Methods:

• A standardized Golden Gate assembly protocol was developed using a 25 μL reaction volume with 40 fmol of input DNA.
• The method accommodates double-stranded DNA (dsDNA) cassettes generated from degenerate oligonucleotides or oligonucleotide pools.
• Scalability of reaction volume and input DNA concentration was assessed without loss in transformation efficiency.

Main Results:

• The standardized method successfully generated libraries on the order of 1 × 10^6 members from a single reaction.
• Scaling up reaction volume and input DNA concentration did not compromise transformation efficiency.
• Custom, user-defined libraries ranging from 10^4 to 10^7 unique protein-encoding variants were constructed for two orthogonal protein engineering systems.

Conclusions:

• The presented standardized Golden Gate method provides a robust and scalable platform for constructing diverse protein-encoding libraries.
• This approach simplifies and enhances the process of protein engineering by enabling the generation of large, user-defined variant libraries.
• The availability of a detailed protocol and general-use destination vectors facilitates broader adoption in scientific research.