Cryo-EM Structure of a Pre-catalytic Human Spliceosome Primed for Activation

Cell. 2017 Aug 10;170(4):701-713.e11. doi: 10.1016/j.cell.2017.07.011.

Karl Bertram ¹, Dmitry E Agafonov ², Olexandr Dybkov ², David Haselbach ¹, Majety N Leelaram ², Cindy L Will ², Henning Urlaub ³, Berthold Kastner ⁴, Reinhard Lührmann ⁵, Holger Stark ⁶

Affiliations

1 Department of Structural Dynamics, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
2 Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
3 Bioanalytical Mass Spectrometry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany; Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075 Göttingen, Germany.
4 Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. Electronic address: b.kastner@mpibpc.mpg.de.
5 Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. Electronic address: reinhard.luehrmann@mpibpc.mpg.de.
6 Department of Structural Dynamics, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. Electronic address: hstark1@gwdg.de.

PMID: 28781166 DOI: 10.1016/j.cell.2017.07.011

Abstract

Little is known about the spliceosome's structure before its extensive remodeling into a catalytically active complex. Here, we report a 3D cryo-EM structure of a pre-catalytic human spliceosomal B complex. The U2 snRNP-containing head domain is connected to the B complex main body via three main bridges. U4/U6.U5 tri-snRNP proteins, which are located in the main body, undergo significant rearrangements during tri-snRNP integration into the B complex. These include formation of a partially closed Prp8 conformation that creates, together with Dim1, a 5' splice site (ss) binding pocket, displacement of Sad1, and rearrangement of Brr2 such that it contacts its U4/U6 substrate and is poised for the subsequent spliceosome activation step. The molecular organization of several B-specific proteins suggests that they are involved in negatively regulating Brr2, positioning the U6/5'ss helix, and stabilizing the B complex structure. Our results indicate significant differences between the early activation phase of human and yeast spliceosomes.

Keywords

B complex spliceosome; B-specific proteins; cryo-EM; pre-catalytic spliceosome; pre-mRNA splicing; spliceosome; spliceosome structure.

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