Structural Biology

Bacteriophage fights back

See allHide authors and affiliations

Science  09 Sep 2016:
Vol. 353, Issue 6304, pp. 1110-1111
DOI: 10.1126/science.353.6304.1110-g

Bacteria and archaea have CRISPR-Cas systems that target and destroy invading DNA from phages and plasmids. However, invaders can fight back. Wang et al. report a structure that shows how the bacteriophage protein AcrF3 inhibits Pseudomonas aeruginosa Cas3 (PaCas3). The Cascade protein complex recruits Cas3 to target DNA. In addition to binding to a protein in Cascade, Cas3 also binds the nontarget DNA strand. There, Cas3 uses its ATP-driven helicase domain to open up the DNA and its nuclease domain to degrade it. The structure showed an AcrF3 dimer complexed to ADP-bound PaCas3, thus locking it in an inactive conformation. Moreover, AcrF3 blocked both the DNA and the protein binding sites involved in recruiting Cas3 to target DNA.

Nat. Struct. Mol. Biol. 10.1038/nsmb.3269 (2016).

Navigate This Article