Structural basis for m(3)G-cap-mediated nuclear import of spliceosomal UsnRNPs by snurportin1Strasser, A., Dickmanns, A., Luehrmann, R., Ficner, R.
(2005) EMBO J 24: 2235-2243
- PubMed: 15920472
- DOI: 10.1038/sj.emboj.7600701
- Primary Citation of Related Structures:
- PubMed Abstract:
- Purification, crystallization and preliminary crystallographic data of the m3G cap-binding domain of human snRNP import factor snurportin 1
Strasser, A., Dickmanns, A., Schmidt, U., Penka, E., Urlaub, H., Sekine, M., Luehrmann, R., Ficner, R.
(2004) Acta Crystallogr D Biol Crystallogr 60: 1628
- Snurportin1, an m3G-cap-specific nuclear import receptor with a novel domain structure
Huber, J., Cronshagen, U., Kadokura, M., Marshallsay, C., Wada, T., Sekine, M., Luehrmann, R.
(1998) EMBO J 17: 4114
In higher eukaryotes the biogenesis of spliceosomal UsnRNPs involves a nucleocytoplasmic shuttling cycle. After the m7G-cap-dependent export of the snRNAs U1, U2, U4 and U5 to the cytoplasm, each of these snRNAs associates with seven Sm proteins. Subsequ ...
In higher eukaryotes the biogenesis of spliceosomal UsnRNPs involves a nucleocytoplasmic shuttling cycle. After the m7G-cap-dependent export of the snRNAs U1, U2, U4 and U5 to the cytoplasm, each of these snRNAs associates with seven Sm proteins. Subsequently, the m7G-cap is hypermethylated to the 2,2,7-trimethylguanosine (m3G)-cap. The import adaptor snurportin1 recognises the m3G-cap and facilitates the nuclear import of the UsnRNPs by binding to importin-beta. Here we report the crystal structure of the m3G-cap-binding domain of snurportin1 with bound m3GpppG at 2.4 A resolution, revealing a structural similarity to the mRNA-guanyly-transferase. Snurportin1 binds both the hypermethylated cap and the first nucleotide of the RNA in a stacked conformation. This binding mode differs significantly from that of the m7G-cap-binding proteins Cap-binding protein 20 (CBP20), eukaryotic initiation factor 4E (eIF4E) and viral protein 39 (VP39). The specificity of the m3G-cap recognition by snurportin1 was evaluated by fluorescence spectroscopy, demonstrating the importance of a highly solvent exposed tryptophan for the discrimination of m7G-capped RNAs. The critical role of this tryptophan and as well of a tryptophan continuing the RNA base stack was confirmed by nuclear import assays and cap-binding activity tests using several snurportin1 mutants.
Department of Molecular Structural Biology, Institute for Microbiology and Genetics, University Göttingen, Germany.