Insights into the mechanism of a G-quadruplex-unwinding DEAH-box helicase. 2015

Michael C Chen, and Pierre Murat, and Keren Abecassis, and Adrian R Ferré-D'Amaré, and Shankar Balasubramanian
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK National Heart, Lung and Blood Institute, 50 South Drive, MSC-8012, Bethesda, MD 20892-8012, USA.

The unwinding of nucleic acid secondary structures within cells is crucial to maintain genomic integrity and prevent abortive transcription and translation initiation. DHX36, also known as RHAU or G4R1, is a DEAH-box ATP-dependent helicase highly specific for DNA and RNA G-quadruplexes (G4s). A fundamental mechanistic understanding of the interaction between helicases and their G4 substrates is important to elucidate G4 biology and pave the way toward G4-targeted therapies. Here we analyze how the thermodynamic stability of G4 substrates affects binding and unwinding by DHX36. We modulated the stability of the G4 substrates by varying the sequence and the number of G-tetrads and by using small, G4-stabilizing molecules. We found an inverse correlation between the thermodynamic stability of the G4 substrates and rates of unwinding by DHX36. In stark contrast, the ATPase activity of the helicase was largely independent of substrate stability pointing toward a decoupling mechanism akin to what has been observed for many double-stranded DEAD-box RNA helicases. Our study provides the first evidence that DHX36 uses a local, non-processive mechanism to unwind G4 substrates, reminiscent of that of eukaryotic initiation factor 4A (eIF4A) on double-stranded substrates.

UI MeSH Term Description Entries
D008024 Ligands A molecule that binds to another molecule, used especially to refer to a small molecule that binds specifically to a larger molecule, e.g., an antigen binding to an antibody, a hormone or neurotransmitter binding to a receptor, or a substrate or allosteric effector binding to an enzyme. Ligands are also molecules that donate or accept a pair of electrons to form a coordinate covalent bond with the central metal atom of a coordination complex. (From Dorland, 27th ed) Ligand
D000255 Adenosine Triphosphate An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter. ATP,Adenosine Triphosphate, Calcium Salt,Adenosine Triphosphate, Chromium Salt,Adenosine Triphosphate, Magnesium Salt,Adenosine Triphosphate, Manganese Salt,Adenylpyrophosphate,CaATP,CrATP,Manganese Adenosine Triphosphate,MgATP,MnATP,ATP-MgCl2,Adenosine Triphosphate, Chromium Ammonium Salt,Adenosine Triphosphate, Magnesium Chloride,Atriphos,Chromium Adenosine Triphosphate,Cr(H2O)4 ATP,Magnesium Adenosine Triphosphate,Striadyne,ATP MgCl2
D013696 Temperature The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms. Temperatures
D053487 DEAD-box RNA Helicases A large family of RNA helicases that share a common protein motif with the single letter amino acid sequence D-E-A-D (Asp-Glu-Ala-Asp). In addition to RNA helicase activity, members of the DEAD-box family participate in other aspects of RNA metabolism and regulation of RNA function. DEAD-box RNA Helicase,DEAD Box Helicase p68,p68 DEAD Box Protein,p68 RNA Helicase,DEAD box RNA Helicase,DEAD box RNA Helicases,Helicase, DEAD-box RNA,Helicase, p68 RNA,Helicases, DEAD-box RNA,RNA Helicase, DEAD-box,RNA Helicase, p68,RNA Helicases, DEAD-box
D054856 G-Quadruplexes Higher-order DNA and RNA structures formed from guanine-rich sequences. They are formed around a core of at least 2 stacked tetrads of hydrogen-bonded GUANINE bases. They can be formed from one two or four separate strands of DNA (or RNA) and can display a wide variety of topologies, which are a consequence of various combinations of strand direction, length, and sequence. (From Nucleic Acids Res. 2006;34(19):5402-15) DNA G-Quadruplexes,DNA, Quadruplex,G-Quadruplexes, DNA,G-Quadruplexes, RNA,Guanine-Quadruplexes,Guanine-Quartets,Guanine-Tetrads,Quadruplex DNA,RNA, G-Quadruplexes,Tetraplex DNA,DNA G Quadruplexes,DNA, Tetraplex,G Quadruplexes,G Quadruplexes, DNA,G Quadruplexes, RNA,G-Quadruplexes RNA,G-Quadruplexes RNAs,Guanine Quadruplexes,Guanine Quartets,Guanine Tetrads,Guanine-Quartet,Guanine-Tetrad,RNA G-Quadruplexes,RNA, G Quadruplexes,RNAs, G-Quadruplexes

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