The toposiomerase IIIalpha-RMI1-RMI2 complex orients human Bloom\u2019s syndrome helicase for efficient disruption of D-loops

Gábor M Harami,Hajnalka Harami-Papp,Keir C Neuman,Yeonee Seol,Zoltán J Kovács,Máté Gyimesi,Mihály Kovács,János Pálinkás

doi:10.1038/s41467-022-28208-9

Abstract

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 IIIα-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.

Highlights

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
We demonstrated that RecQ efficiently disrupts displacement loops (D-loops)-like structures by removing strand invasions, and that this activity is mediated by its HRDC domain[19]
BLM was shown to facilitate DNA-repair synthesis in vitro[11], which could lead to stabilization of D-loop structures in an in vivo context, suggesting differences in D-loop processing by BLM and RecQ

Summary

Introduction

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. Human Bloom’s syndrome (BLM, RecQ family) helicase plays central roles in HR pathway selection and quality control via unexplored molecular mechanisms. We show that BLM’s multidomain 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 IIIα-RMI1-RMI2, which have been shown to be involved in multiple steps of HR-based DNA repair. BLM helicase safeguards genome stability by playing key roles in homologous recombination (HR)-based repair of doublestranded (ds) DNA breaks (DSBs), the restart of stalled replication forks, and in the completion of chromosome replication[1]. An in vivo study highlighted that BLM regulates RAD51 filaments either by inhibiting their formation or facilitating their dissociation[10]

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