352d

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spinqualitylabelsall models 352d, resolution 0.950Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

THE CRYSTAL STRUCTURE OF A PARALLEL-STRANDED PARALLEL-STRANDED GUANINE TETRAPLEX AT 0.95 ANGSTROM RESOLUTION

Overview

In both DNA and RNA, stretches of guanine bases can form stable, four-stranded helices in the presence of sodium or potassium ions., Sequences with a propensity to form guanine tetraplexes have been found in, chromosomal telomers, immunoglobulin switch regions, and recombination, sites. We report the crystal structure at 0.95 A resolution of a, parallel-stranded tetraplex formed by the hexanucleotide d(TG4T) in the, presence of sodium ions. The four strands form a right-handed helix that, is stabilized by hydrogen-bonding tetrads of co-planar guanine bases., Well-resolved sodium ions are found between and, at defined points, within, tetrad planes and are coordinated with the guanine O6 groups. Nine calcium, ions have been identified, each with a well-defined hepta-coordinate, hydration shell. Hydrogen-bonding water patterns are observed within the, tetraplex's helical grooves and clustered about the phosphate groups., Water molecules in the groove may form a hydrogen bond with the O4', and, may affect the stacking behavior of guanine. Two distinct stacking, arrangements are noted for the guanine tetrads. The thymine bases do not, contribute to the four-stranded conformation, but instead stack to, stabilize the crystal lattice. We present evidence that the sugar, conformation is strained and propose that this originates from forces that, optimize guanine base stacking. Discrete conformational disorder is, observed at several places in the phosphodiester backbone, which results, from a simple crankshaft rotation that requires no net change in the sugar, conformation.

About this Structure

352D is a Protein complex structure of sequences from [1] with and as ligands. Full crystallographic information is available from OCA.

Reference

The crystal structure of a parallel-stranded guanine tetraplex at 0.95 A resolution., Phillips K, Dauter Z, Murchie AI, Lilley DM, Luisi B, J Mol Biol. 1997 Oct 17;273(1):171-82. PMID:9367755

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