title: RecQ-core of BLM unfolds telomeric G-quadruplex in the absence of ATP.
abstract: Various helicases and single-stranded DNA (ssDNA) binding proteins are known to destabilize G-quadruplex (GQ) structures, which otherwise result in genomic instability. Bulk biochemical studies have shown that Bloom helicase (BLM) unfolds both intermolecular and intramolecular GQ in the presence of ATP. Using single molecule FRET, we show that binding of RecQ-core of BLM (will be referred to as BLM) to ssDNA in the vicinity of an intramolecular GQ leads to destabilization and unfolding of the GQ in the absence of ATP. We show that the efficiency of BLM-mediated GQ unfolding correlates with the binding stability of BLM to ssDNA overhang, as modulated by the nucleotide state, ionic conditions, overhang length and overhang directionality. In particular, we observed enhanced GQ unfolding by BLM in the presence of non-hydrolysable ATP analogs, which has implications for the underlying mechanism. We also show that increasing GQ stability, via shorter loops or higher ionic strength, reduces BLM-mediated GQ unfolding. Finally, we show that while WRN has similar activity as BLM, RecQ and RECQ5 helicases do not unfold GQ in the absence of ATP at physiological ionic strength. In summary, our study points to a novel and potentially very common mechanism of GQ destabilization mediated by proteins binding to the vicinity of these structures.
authors.affiliation: Department of Physics, Kent State University, Kent, OH 44242, USA.
authors.forename: Jagat B
authors.initials: JB
authors.lastname: Budhathoki
authors.affiliation: Department of Physics, Kent State University, Kent, OH 44242, USA.
authors.forename: Sujay
authors.initials: S
authors.lastname: Ray
authors.affiliation: Institute of Molecular Genetics AS CR, Prague, Czech Republic.
authors.forename: Vaclav
authors.initials: V
authors.lastname: Urban
authors.affiliation: Institute of Molecular Genetics AS CR, Prague, Czech Republic Institute of Molecular Cancer Research, University of Zurich, Zurich, Switzerland.
authors.forename: Pavel
authors.initials: P
authors.lastname: Janscak
authors.affiliation: Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA hbalci@kent.edu.
authors.forename: Jaya G
authors.initials: JG
authors.lastname: Yodh
authors.affiliation: Department of Physics, Kent State University, Kent, OH 44242, USA hbalci@kent.edu.
authors.forename: Hamza
authors.initials: H
authors.lastname: Balci
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D054856:G-Quadruplexes; D006801:Humans; D053484:RecQ Helicases / Q000737:chemistry / Q000378:metabolism*; D016615:Telomere / Q000737:chemistry*
chemical_list: D004277:DNA, Single-Stranded; C022571:adenosine 5'-O-(3-thiotriphosphate); D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; C097151:Bloom syndrome protein; D053484:RecQ Helicases