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Topology Variation and Loop Structural Homology in Crystal and Simulated Structures of a Bimolecular DNA Quadruplex
journal contribution
posted on 2006-04-26, 00:00 authored by Pascale Hazel, Gary N. Parkinson, Stephen NeidleThe topology of DNA quadruplexes depends on the nature and number of the nucleotides linking
G-quartet motifs. To assess the effects of a three-nucleotide TTT linker, the crystal structure of the DNA
sequence d(G4T3G4) has been determined at 1.5 Å resolution, together with that of the brominated analogue
d(G4BrUTTG4) at 2.4 Å resolution. Both sequences form bimolecular intermolecular G-quadruplexes with
lateral loops. d(G4BrUTTG4) crystallized in the monoclinic space group P21 with three quadruplex molecules
in the asymmetric unit, two associating together as a head-to-head stacked dimer, and the third as a single
head-to-tail dimer. The head-to-head dimers have two lateral loops on the same G-quadruplex face and
form an eight-G-quartet stack, with a linear array of seven K+ ions between the quartets. d(G4T3G4)
crystallized in the orthorhombic space group C222 and has a structure very similar to the head-to-tail dimer
in the P21 unit cell. The sequence studied here is able to form several different folds; however, all four
quadruplexes in the two structures have lateral loops, in contrast to the diagonal loops reported for the
analogous quadruplex with T4 loops. A total of seven independent T3 loops were observed in the two
structures. These can be classified into two discrete conformational classes, suggesting that these represent
preferred loop conformations that are independent of crystal-packing forces.
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DNA quadruplexesspace group C 222quadruplex moleculesT 4 loops1.5 Å resolutionbrominated analoguedimerTopology VariationBimolecular DNA Quadruplexsequences formTTTUTTGLoop Structural HomologyDNA sequencecrystal structureT 3 loopsP 2 1 unit cellspace group P 2 12.4 Å resolutionSimulated Structuresloop conformations
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