RQC helical hairpin in Bloom's syndrome helicase regulates DNA unwinding by dynamically intercepting nascent nucleotides

Jianbing Ma; Chunhua Xu; Jinghua Li; Xi-Miao Hou; Lin-Tai Da; Qi Jia; Xingyuan Huang; Jin Yu; Xuguang Xi; Ying Lu; Ming Li

doi:10.1016/j.isci.2021.103606

RQC helical hairpin in Bloom's syndrome helicase regulates DNA unwinding by dynamically intercepting nascent nucleotides

iScience. 2021 Dec 10;25(1):103606. doi: 10.1016/j.isci.2021.103606. eCollection 2022 Jan 21.

Authors

Jianbing Ma^{1

2}, Chunhua Xu², Jinghua Li², Xi-Miao Hou³, Lin-Tai Da⁴, Qi Jia^{1

2

5}, Xingyuan Huang^{2

5}, Jin Yu⁶, Xuguang Xi⁷, Ying Lu^{1

2

5}, Ming Li^{1

2

5}

Affiliations

¹ Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China.
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
³ College of Life Sciences, Northwest A&F University, Yangling 712100, Shaanxi, China.
⁴ Key Laboratory of System Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, Shanghai 200240, China.
⁵ University of Chinese Academy of Sciences, Beijing 100049, China.
⁶ Department of Physics and Astronomy, Department of Chemistry, NSF-Simons Center for Multiscale Cell Fate Research, University of California, Irvine, CA 92697, USA.
⁷ LBPA, ENS de Cachan, CNRS, Université Paris-Saclay, Cachan 94235, France.

Abstract

The RecQ family of helicases are important for maintenance of genomic integrity. Although functions of constructive subdomains of this family of helicases have been extensively studied, the helical hairpin (HH) in the RecQ-C-terminal domain (RQC) has been underappreciated and remains poorly understood. Here by using single-molecule fluorescence resonance energy transfer, we found that HH in the human BLM transiently intercepts different numbers of nucleotides when it is unwinding a double-stranded DNA. Single-site mutations in HH that disrupt hydrogen bonds and/or salt bridges between DNA and HH change the DNA binding conformations and the unwinding features significantly. Our results, together with recent clinical tests that correlate single-site mutations in HH of human BLM with the phenotype of cancer-predisposing syndrome or Bloom's syndrome, implicate pivotal roles of HH in BLM's DNA unwinding activity. Similar mechanisms might also apply to other RecQ family helicases, calling for more attention to the RQC helical hairpin.

Keywords: Analytical chemistry instrumentation; Biochemistry; Biological sciences; Structural biology.