1DQH: Crystal Structure Of Helix Ii Of The X. Laevis Somatic 5s Rrna With A Cytosine Bulge In Two Conformations

The crystal structure of r(GCCACCCUG).r(CAGGGUCGGC), helix II of the Xenopus laevis 5S rRNA with a cytosine bulge (underlined), has been determined in two forms at 2.2 A (Form I, space group P4(2)2(1)2, a = b = 57.15 A and c = 43.54 A) and 1.7 A (Form II, space group P4(3)2(1)2, a = b = 32.78 A and c = 102.5 A). The helical regions of the nonamers are found in the standard A-RNA conformations and the two forms have an RMS deviation of 0.75 A. However, the cytosine bulge adopts two significantly different conformations with an RMS deviation of 3.9 A. In Form I, the cytosine bulge forms an intermolecular C+*G.C triple in the major groove of a symmetry-related duplex with intermolecular hydrogen bonds between N4C and O6G, and between protonated N3+C and N7G. In contrast, a minor groove C*G.C triple is formed in Form II with intermolecular hydrogen bonds between O2C and N2G, and between N3C and N3G with a water bridge. A partial major groove opening was observed in Form I structure at the bulge site. Two Ca2+ ions were found in Form I helix whereas there were none in Form II. The structural comparison of these two forms indicates that bulged residues can adopt a variety of conformations with little perturbation to the global helix structure. This suggests that bulged residues could function as flexible latches in bridging double helical motifs and facilitate the folding of large RNA molecules.
PDB ID: 1DQHDownload
MMDB ID: 48708
PDB Deposition Date: 2000/1/4
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 1.7  Å
Source Organism:
Biological Unit for 1DQH: dimeric; determined by author
Molecular Components in 1DQH
Label Count Molecule
Nucleotides(2 molecules)
RNA (5'-r(gpcpcpapcpcpcpupg)-3')
Molecule annotation
RNA (5'-r(cpapgpgpgpupcpgpgpc)-3')
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB