Metagenome-Derived CRISPR-Cas12a Mining and Characterization

The advent of clustered regularly interspaced short palindromic repeats (CRISPR)-based technologies has revolutionized genome editing, with continued interest in expanding the CRISPR-associated proteins (Cas) toolbox with diverse, efficient, and specific effectors. CRISPR-Cas12a is a potent, programmable RNA-guided dual nickase, broadly used for genome editing. Here, we mined dairy cow microbial metagenomes for CRISPR-Cas systems, unraveling novel Cas12a enzymes. Using in silico pipelines, we characterized and predicted key drivers of CRISPR-Cas12a activity, encompassing guides and protospacer adjacent motifs for five systems. We next assessed their functional potential in cell-free transcription-translation assays with GFP-based fluorescence readouts. Lastly, we determined their genome editing potential in vivo in Escherichia coli by generating 1 kb knockouts. Unexpectedly, we observed natural sequence variation in the bridge-helix domain of the best-performing candidate and used mutagenesis to alter the activity of Cas12a orthologs, resulting in increased gene editing capabilities of a relatively inefficient candidate. This study illustrates the potential of underexplored metagenomic sequence diversity for the development and refinement of genome editing effectors.