Alternative conformations of Nop56/58-fibrillarin complex and implication for induced-fit assenly of box C/D RNPs
Classification:
TRANSFERASE
Technique:
X-Ray Diffraction
Resolution:
2.7
R value free:
0.265
R value observed:
R value work:
0.234
Abstract of the PDB Structure's related Publication:
The Nop56/58-fibrillarin heterocomplex is a core protein complex of the box C/D ribonucleoprotein particles that modify and process ribosomal RNAs. The previous crystal structure of the Archaeoglobus fulgidus complex revealed a symmetric dimer of two Nop56/58-fibrillarin complexes linked by the coiled-coil domains of the Nop56/68 proteins. However, because the A. fulgidus Nop56/58 protein lacks some domains found in most other species, it was thought that the bipartite architecture of the heterocomplex was not likely a general phenomenon. Here we report the crystal structure of the Nop56/58-fibrillarin complex bound with methylation cofactor, S-adenosyl-L-methionine from Pyrococcus furiosus, at 2.7 A. The new complex confirms the generality of the previously observed bipartite arrangement. In addition however, the conformation of Nop56/58 in the new structure differs substantially from that in the earlier structure. The distinct conformations of Nop56/58 suggest potential flexibility in Nop56/58. Computational normal mode analysis supports this view. Importantly, fibrillarin is repositioned within the two complexes. We propose that hinge motion within Nop56/58 has important implications for the possibility of simultaneously positioning two catalytic sites at the two target sites of a bipartite box C/D guide RNA.
Homologue of yeast Nop1 protein and human fibrillarin. A catalytic subunit of C/D RNP complex, which in Archaea is composed of FlpA (fibrillarin), L7Ae and Nop56/58 proteins.