摘要：SummaryThe 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.Graphical abstractDisplay OmittedHighlights•Single-stranded DNA in the DNA-BLM complex is structurally dynamic•Interactions between helical hairpin of BLM and ssDNA are heterogeneous•Single site mutations in the helical hairpin change the conformation of DNA•The helical hairpin regulates DNA unwinding by dynamically intercepting nascent DNA.Analytical chemistry instrumentation; Biological sciences; Biochemistry; Structural biology
