Targeted mutagenesis and high-throughput screening of diversified gene and promoter libraries for isolating gain-of-function mutations

• Published in: Frontiers in bioengineering and biotechnology Vol. 11; p. 1202388
• Main Authors: Huttanus, Herbert M, Triola, Ellin-Kristina H, Velasquez-Guzman, Jeanette C, Shin, Sang-Min, Granja-Travez, Rommel S, Singh, Anmoldeep, Dale, Taraka, Jha, Ramesh K
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 17.07.2023
• Subjects: Bioengineering and Biotechnology; biological science; fluorescence-activated cell sorting; mutagenesis; overlap extension PCR; overlap oligonucleotide extension; polymerase chain reaction; promoter engineering; protein engineering; synthetic biology; whole-cell biosensors; promoter engineering; synthetic biology; overlap extension PCR; protein engineering; whole-cell biosensor; fluorescence-activated cell sorting; mutagenesis; polymerase chain reaction
• ISSN: 2296-4185; 2296-4185
• DOI: 10.3389/fbioe.2023.1202388

Targeted mutagenesis of a promoter or gene is essential for attaining new functions in microbial and protein engineering efforts. In the burgeoning field of synthetic biology, heterologous genes are expressed in new host organisms. Similarly, natural or designed proteins are mutagenized at targeted positions and screened for gain-of-function mutations. Here, we describe methods to attain complete randomization or controlled mutations in promoters or genes. Combinatorial libraries of one hundred thousands to tens of millions of variants can be created using commercially synthesized oligonucleotides, simply by performing two rounds of polymerase chain reactions. With a suitably engineered reporter in a whole cell, these libraries can be screened rapidly by performing fluorescence-activated cell sorting (FACS). Within a few rounds of positive and negative sorting based on the response from the reporter, the library can rapidly converge to a few optimal or extremely rare variants with desired phenotypes. Library construction, transformation and sequence verification takes 6-9 days and requires only basic molecular biology lab experience. Screening the library by FACS takes 3-5 days and requires training for the specific cytometer used. Further steps after sorting, including colony picking, sequencing, verification, and characterization of individual clones may take longer, depending on number of clones and required experiments.