Crystallization and biophysical characterization of spliceosomal protein complexes
von Andreas Schmitt
Datum der mündl. Prüfung:2014-04-15
Betreuer:Prof. Dr. Ralf Ficner
Gutachter:Prof. Dr. Kai Tittmann
Gutachter:Prof. Dr. Reinhard Lührmann
EnglischmRNA splicing is a highly dynamic process by which non-coding sequences are removed from a pre-mature mRNA. It is catalyzed by the spliceosome, a huge and highly dynamic ribonucleoprotein complex consisting of up to five small nuclear RNAs and more than 100 proteins. For each intron to be excised, the spliceosome has to assemble on the pre-mRNA, catalyze the two steps of the splicing reaction and is disassembled afterwards. The dynamics of the spliceosome are driven and controlled by at least eight conserved DExD/H-box ATPases which remodel RNA-RNA, protein-RNA and protein-protein interactions during assembly, catalysis and disassembly of the spliceosome and are furthermore involved in quality control. The DEAH-box ATPase Prp2 plays a key role in the activation of the spliceosome, as it promotes the transition of the spliceosome from the Bact to the catalytically active B* complex. Prp2 exhibits an RNA-dependent NTPase activity and is active in the spliceosome after binding to its interaction partner, the G-patch containing protein Spp2. The G-patch sequence motif consists of a conserved glycine pattern and is mostly found in proteins involved in RNA processing. So far, the structure of a G-patch motif has been unknown and the function of the G-patch motif in general and in particular of Spp2 remained elusive. Here, the crystal structure of Spp2 from Chaetomium thermophilum in complex with Prp2 is shown, representing the first crystal structure of a G-patch protein. Free Spp2 is intrinsically disordered as demonstrated by CD- and NMR- spectroscopy, but at least its G-patch region adopts a well-defined fold upon binding to Prp2. The interaction with Spp2 induces major structural changes in the beta-hairpin of Prp2, a region which is supposed to move upon ATP binding. However, Spp2 does not affect the ATPase activity or RNA affinity of Prp2 in vitro. Together, these findings give rise to the hypothesis that Spp2 might fulfill the function of an adaptor protein recruiting Prp2 to the spliceosome and transferring mechanical forces generated by ATP hydrolysis to other components of the spliceosome.
Keywords: Helicase; Spliceosome