Uncovering viral sabotage of host crispr-cas immune systems
CRISPR-Cas immune system represents one of the most effective weapons against mobile genetic elements in the host defense arsenal. Bacteriophages (phages) armed with anti-CRISPR proteins can, however, inhibit CRISPR immunity by sabotaging components of the immune system with evolutionary advantages. This proposal sets out to discover novel phage-encoded anti-CRISPR proteins and understand the molecular mechanisms of the inhibitory processes.
I will focus on novel anti-CRISPR proteins for Cas9-containing type II CRISPR-Cas systems in lactic acid bacteria (LAB). I expect anti-CRISPR proteins to be present in phages for LAB, for which the CRISPR system is an important line of defense. It is highly plausible that LAB-infecting phages have evolved to possess anti-CRISPR proteins. However, none of anti-CRISPR proteins against type II CRISPR have been described so far. To identify novel type II anti-CRISPR proteins encoded by phage genomes and explore novel features of the anti-CRISPR proteins, I will establish high-throughput screening methods using an integrated approach consisting of metagenomics, bioinformatics and mass spectrometry. After identifying candidate anti-CRISPR proteins, I will uncover the underlying molecular mechanisms of these viral anti-CRISPR proteins utilizing state-of-the-art single-molecule fluorescence methodologies.	
The fierce virus–host arms race has resulted in high diversity of distinct prokaryotic CRISPR-Cas systems. Therefore, I anticipate that my high-throughput screening will lead to discovery of remarkably diverse anti-CRISPR proteins, specifically anti-CRISPR variants targeting Cas9. The proposed combination of viral diversity screening and single-molecule approaches will reveal novel mechanisms of anti-CRISPR activity that are difficult to obtain by traditional biochemistry, will impact potential applications of Cas9, and will provide unique insights into the host-virus arms race.