The toposiomerase IIIalpha-RMI1-RMI2 complex orients human Bloom's syndrome helicase for efficient disruption of D-loops

Human Bloom's syndrome (BLM) helicase has a role in DNA repair, and BLM deficiency in humans is associated with chromosomal abnormalities. Here the authors employ solution biophysical assays to show BLM maintains a balance for disruption and stabilization of oligonucleotide-based D-loops. Interaction with the Topoisomerase IIIalpha-RMI1-RMI2 complex orients the activity toward D-loop disruption. Homologous recombination (HR) is a ubiquitous and efficient process that serves the repair of severe forms of DNA damage and the generation of genetic diversity during meiosis. HR can proceed via multiple pathways with different outcomes that may aid or impair genome stability and faithful inheritance, underscoring the importance of HR quality control. Human Bloom's syndrome (BLM, RecQ family) helicase plays central roles in HR pathway selection and quality control via unexplored molecular mechanisms. Here we show that BLM's multi-domain structural architecture supports a balance between stabilization and disruption of displacement loops (D-loops), early HR intermediates that are key targets for HR regulation. We find that this balance is markedly shifted toward efficient D-loop disruption by the presence of BLM's interaction partners Topoisomerase III alpha-RMI1-RMI2, which have been shown to be involved in multiple steps of HR-based DNA repair. Our results point to a mechanism whereby BLM can differentially process D-loops and support HR control depending on cellular regulatory mechanisms.

Automated summary

In this study, the researchers found that human Bloom's syndrome helicase plays a role in the processing of displacement loops during DNA repair, depending on cellular regulatory mechanisms. In the presence of interaction partners Topoisomerase III alpha-RMI1-RMI2, the helicase's activity shifts towards efficient disruption of displacement loops, aiding genome stability and faithful inheritance.