Structural basis of G-quadruplex unfolding by the DEAH/RHA helicase DHX36

Nature. 2018 Jun;558(7710):465-469. doi: 10.1038/s41586-018-0209-9. Epub 2018 Jun 13.

Abstract

Guanine-rich nucleic acid sequences challenge the replication, transcription, and translation machinery by spontaneously folding into G-quadruplexes, the unfolding of which requires forces greater than most polymerases can exert1,2. Eukaryotic cells contain numerous helicases that can unfold G-quadruplexes 3 . The molecular basis of the recognition and unfolding of G-quadruplexes by helicases remains poorly understood. DHX36 (also known as RHAU and G4R1), a member of the DEAH/RHA family of helicases, binds both DNA and RNA G-quadruplexes with extremely high affinity4-6, is consistently found bound to G-quadruplexes in cells7,8, and is a major source of G-quadruplex unfolding activity in HeLa cell lysates 6 . DHX36 is a multi-functional helicase that has been implicated in G-quadruplex-mediated transcriptional and post-transcriptional regulation, and is essential for heart development, haematopoiesis, and embryogenesis in mice9-12. Here we report the co-crystal structure of bovine DHX36 bound to a DNA with a G-quadruplex and a 3' single-stranded DNA segment. We show that the N-terminal DHX36-specific motif folds into a DNA-binding-induced α-helix that, together with the OB-fold-like subdomain, selectively binds parallel G-quadruplexes. Comparison with unliganded and ATP-analogue-bound DHX36 structures, together with single-molecule fluorescence resonance energy transfer (FRET) analysis, suggests that G-quadruplex binding alone induces rearrangements of the helicase core; by pulling on the single-stranded DNA tail, these rearrangements drive G-quadruplex unfolding one residue at a time.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Motifs
  • Animals
  • Cattle
  • Crystallography, X-Ray
  • DEAD-box RNA Helicases / chemistry*
  • DEAD-box RNA Helicases / genetics
  • DEAD-box RNA Helicases / metabolism*
  • DNA / chemistry*
  • DNA / metabolism*
  • Fluorescence Resonance Energy Transfer
  • G-Quadruplexes*
  • Models, Molecular
  • Mutation
  • Nucleic Acid Denaturation*

Substances

  • DNA
  • DEAD-box RNA Helicases