For many bacteria, one line of defense against viral infection is a sophisticated RNA-guided “immune system” called CRISPR-Cas. At the center of this system is a surveillance complex that recognizes viral DNA and triggers its destruction. However, viruses can strike back and disable this surveillance complex using “anti-CRISPR” proteins, though no one has figured out exactly how these anti-CRISPRs work—until now. For the first time, researchers have solved the structure of viral anti-CRISPR proteins attached to a bacterial CRISPR surveillance complex, revealing precisely how viruses incapacitate the bacterial defense system. The research team, co-led by biologist Gabriel C. Lander, Ph.D., of The Scripps Research Institute (TSRI), discovered that anti-CRISPR proteins work by locking down CRISPR’s ability to identify and attack the viral genome. One anti-CRISPR protein even “mimics” DNA to throw the CRISPR-guided detection machine off its trail. “It’s amazing what these systems do to one-up each other,” said Dr. Lander. “It all comes back to this evolutionary arms race." The new research, co-led by Blake Wiedenheft, Ph.D., of Montana State University, was published in the March 23, 2017 issue of Cell. The article is titled “Structure Reveals Mechanisms of Viral Suppressors that Intercept a CRISPR RNA-Guided Surveillance Complex.” If CRISPR complexes sound familiar, that’s because they are at the forefront in a new wave of genome-editing technologies. CRISPR stands for “clustered regularly interspaced short palindromic repeats.” Scientists have discovered that they can take advantage of CRISPR’s natural ability to degrade sections of viral RNA and use CRISPR systems to remove unwanted genes from nearly any organism.
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