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Publications of the Week

Small-Molecule Sensitization of RecBCD Helicase–Nuclease to a Chi Hotspot-Activated State

By July 17, 2020No Comments

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This week we profile a recent publication in Nucleic Acids Research
from the laboratory of Dr. Gerry Smith (pictured, far left) at Fred Hutch.

Can you provide a brief overview of your lab’s current research focus?

We study the molecular mechanisms of DNA break repair and genetic recombination in bacteria and fission yeast.

What is the significance of the findings in this publication?

We study a small molecule (NSAC1003) that one of our collaborators (Ryan Cirz) at Achaogen, Inc., found in a screen for inhibitors of the E. coli DNA break repair enzyme RecBCD, a helicase-nuclease.  This compound mimics two RecBCD mutations that make RecBCD cut DNA at novel positions much like the uninhibited, wild-type enzyme cuts at Chi hotspots of genetic recombination.  The novel cuts are at a certain percent of the length of the DNA substrate used in the assay.  Figuring out how the two mutant enzymes measure the length of DNA and calculate a certain percent (19% in one mutant and 6% in the other) led us to a new model for how Chi controls RecBCD (our “signal transduction” model).  The effect of compound NSAC1003 on RecBCD bolsters this model by showing an additional way in which the enzyme can be activated to cut DNA, an early step in repair of broken DNA and making genetic recombinants.

What are the next steps for this research?

Testing more directly, e.g., by X-ray crystallography, the hypothesized binding of NSAC1003 in the ATP-binding site (ATPase) of RecB, one of RecBCD’s two helicases (the two mutants mentioned above change amino acids in this site).  Finding other compounds that behave similarly.

This work was funded by:

Research grant from NIH (R35 GM118120, GR Smith, PI).

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