8r0b
Cryo-EM structure of the cross-exon pre-B+ATP complex
Structural highlights
DiseasePRP8_HUMAN Defects in PRPF8 are the cause of retinitis pigmentosa type 13 (RP13) [MIM:600059. RP leads to degeneration of retinal photoreceptor cells. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well. RP13 inheritance is autosomal dominant.[1] [2] [:][3] [4] FunctionPRP8_HUMAN Central component of the spliceosome, which may play a role in aligning the pre-mRNA 5'- and 3'-exons for ligation. Interacts with U5 snRNA, and with pre-mRNA 5'-splice sites in B spliceosomes and 3'-splice sites in C spliceosomes. Publication Abstract from PubMedEarly spliceosome assembly can occur through an intron-defined pathway, whereby U1 and U2 small nuclear ribonucleoprotein particles (snRNPs) assemble across the intron(1). Alternatively, it can occur through an exon-defined pathway(2-5), whereby U2 binds the branch site located upstream of the defined exon and U1 snRNP interacts with the 5' splice site located directly downstream of it. The U4/U6.U5 tri-snRNP subsequently binds to produce a cross-intron (CI) or cross-exon (CE) pre-B complex, which is then converted to the spliceosomal B complex(6,7). Exon definition promotes the splicing of upstream introns(2,8,9) and plays a key part in alternative splicing regulation(10-16). However, the three-dimensional structure of exon-defined spliceosomal complexes and the molecular mechanism of the conversion from a CE-organized to a CI-organized spliceosome, a pre-requisite for splicing catalysis, remain poorly understood. Here cryo-electron microscopy analyses of human CE pre-B complex and B-like complexes reveal extensive structural similarities with their CI counterparts. The results indicate that the CE and CI spliceosome assembly pathways converge already at the pre-B stage. Add-back experiments using purified CE pre-B complexes, coupled with cryo-electron microscopy, elucidate the order of the extensive remodelling events that accompany the formation of B complexes and B-like complexes. The molecular triggers and roles of B-specific proteins in these rearrangements are also identified. We show that CE pre-B complexes can productively bind in trans to a U1 snRNP-bound 5' splice site. Together, our studies provide new mechanistic insights into the CE to CI switch during spliceosome assembly and its effect on pre-mRNA splice site pairing at this stage. Structural insights into the cross-exon to cross-intron spliceosome switch.,Zhang Z, Kumar V, Dybkov O, Will CL, Zhong J, Ludwig SEJ, Urlaub H, Kastner B, Stark H, Luhrmann R Nature. 2024 May 22. doi: 10.1038/s41586-024-07458-1. PMID:38778104[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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