Structural analysis of the assembly machinery of spliceosomal U snRNPs
Final Report Abstract
Small nuclear ribonucleoproteins (snRNPs) represent major constituents of major and minor spliceosomes. SnRNPs contain a common core, composed of seven Sm proteins bound to snRNA, which forms in a step-wise and factor mediated reaction. The assembly chaperone pICln initially mediates the formation of an otherwise unstable pentameric Sm-protein unit. This so-called 6S complex docks subsequently onto the SMN-complex, which removes pICln and enables the transfer of pre-assembled Sm proteins onto snRNA. In this DFG grant proposal we used X-ray crystallography and electron microscopy to investigate the structural basis of snRNP assembly. We succeeded to crystallize and determine the structure of two key assembly intermediates of the assisted assembly of snRNPs. The first structure we solved was from the 6S complex, which identified the assembly chaperone pICln as an Sm-protein mimic. This property allows pICln to act as a topological organizer of the Sm pentamer in a closed ring. A second structure of 6S bound to the SMN-complex components SMN and Gemin2 (termed 8S complex) uncovered the likely mechanism of pICln elimination and Sm protein activation for snRNA binding. Our studies reveal how assembly factors facilitate formation of RNA-protein complexes in vivo.
Publications
- 2010. A crystallization screen based on alternative polymeric precipitants. Acta Crystallogr D Biol Crystallogr. 66 (Pt 6):685-697
Grimm, C., Chari, A., Reuter, K. and Fischer, U.
(See online at https://doi.org/10.1107/S0907444910009005) - 2011. Structural basis for dimethylarginine recognition by the Tudor domains of human SMN and SPF30 proteins. Nat Struct Mol Biol. 18(12):1414-1420
Tripsianes, K., Madl, T., Machyna, M., Fessas, D., Englbrecht, C., Fischer, U., Neugebauer, KM. and Sattler, M.
(See online at https://doi.org/10.1038/nsmb.2185) - 2013. Mutations in SNRPE, which encodes a core protein of the spliceosome, cause autosomal-dominant hypotrichosis simplex. Am J Hum Genet. 10;92(1):81-87
Pasternack SM, Refke M, Paknia E, Hennies HC, Franz T, Schäfer N, Fryer A, van Steensel M, Sweeney E, Just M, Grimm C, Kruse R, Ferrándiz C, Nöthen MM, Fischer U, Betz RC
(See online at https://doi.org/10.1016/j.ajhg.2012.10.022) - 2013. Structural Basis of Assembly Chaperone-Mediated snRNP Formation. Mol Cell. 21;49(4):692-703
Grimm C, Chari A, Pelz JP, Kuper J, Kisker C, Diederichs K, Stark H, Schindelin H, Fischer U
(See online at https://doi.org/10.1016/j.molcel.2012.12.009)
