DSSR-PyMOL cartoon-block schematics: PDB entry 7qtt

PDB-id

7qtt; DSSR-derived features in text and JSON formats

Class

splicing

Method

cryo-EM (3.1 Å)

Summary

Structural organization of a late activated human spliceosome (baqr, core region)

Reference

Schmitzova J, Cretu C, Dienemann C, Urlaub H, Pena V (2023): "Structural basis of catalytic activation in human splicing." Nature, 617, 842-850. doi: 10.1038/s41586-023-06049-w.

Abstract

Pre-mRNA splicing follows a pathway driven by ATP-dependent RNA helicases. A crucial event of the splicing pathway is the catalytic activation, which takes place at the transition between the activated B_act and the branching-competent B_* spliceosomes. Catalytic activation occurs through an ATP-dependent remodelling mediated by the helicase PRP2 (also known as DHX16)_1-3. However, because PRP2 is observed only at the periphery of spliceosomes_3-5, its function has remained elusive. Here we show that catalytic activation occurs in two ATP-dependent stages driven by two helicases: PRP2 and Aquarius. The role of Aquarius in splicing has been enigmatic_6,7. Here the inactivation of Aquarius leads to the stalling of a spliceosome intermediate-the B_AQR complex-found halfway through the catalytic activation process. The cryogenic electron microscopy structure of B_AQR reveals how PRP2 and Aquarius remodel B_act and B_AQR, respectively. Notably, PRP2 translocates along the intron while it strips away the RES complex, opens the SF3B1 clamp and unfastens the branch helix. Translocation terminates six nucleotides downstream of the branch site through an assembly of PPIL4, SKIP and the amino-terminal domain of PRP2. Finally, Aquarius enables the dissociation of PRP2, plus the SF3A and SF3B complexes, which promotes the relocation of the branch duplex for catalysis. This work elucidates catalytic activation in human splicing, reveals how a DEAH helicase operates and provides a paradigm for how helicases can coordinate their activities.