7px3
Structure of U5 snRNP assembly and recycling factor TSSC4 in complex with BRR2 and Jab1 domain of PRPF8
Structural highlights
FunctionTSSC4_HUMAN Protein associated with the U5 snRNP, during its maturation and its post-splicing recycling and which is required for spliceosomal tri-snRNP complex assembly in the nucleus (PubMed:34131137, PubMed:35188580). Has a molecular sequestering activity and transiently hinders SNRNP200 binding sites for constitutive splicing factors that intervene later during the assembly of the spliceosome and splicing (PubMed:35188580). Together with its molecular sequestering activity, may also function as a molecular adapter and placeholder, coordinating the assembly of the U5 snRNP and its association with the U4/U6 di-snRNP (PubMed:34131137).[1] [2] Publication Abstract from PubMedBiogenesis of spliceosomal small nuclear ribonucleoproteins (snRNPs) and their recycling after splicing require numerous assembly/recycling factors whose modes of action are often poorly understood. The intrinsically disordered TSSC4 protein has been identified as a nuclear-localized U5 snRNP and U4/U6-U5 tri-snRNP assembly/recycling factor, but how TSSC4's intrinsic disorder supports TSSC4 functions remains unknown. Using diverse interaction assays and cryogenic electron microscopy-based structural analysis, we show that TSSC4 employs four conserved, non-contiguous regions to bind the PRPF8 Jab1/MPN domain and the SNRNP200 helicase at functionally important sites. It thereby inhibits SNRNP200 helicase activity, spatially aligns the proteins, coordinates formation of a U5 sub-module and transiently blocks premature interaction of SNRNP200 with at least three other spliceosomal factors. Guided by the structure, we designed a TSSC4 variant that lacks stable binding to the PRPF8 Jab1/MPN domain or SNRNP200 in vitro. Comparative immunoprecipitation/mass spectrometry from HEK293 nuclear extract revealed distinct interaction profiles of wild type TSSC4 and the variant deficient in PRPF8/SNRNP200 binding with snRNP proteins, other spliceosomal proteins as well as snRNP assembly/recycling factors and chaperones. Our findings elucidate molecular strategies employed by an intrinsically disordered protein to promote snRNP assembly, and suggest multiple TSSC4-dependent stages during snRNP assembly/recycling. The intrinsically disordered TSSC4 protein acts as a helicase inhibitor, placeholder and multi-interaction coordinator during snRNP assembly and recycling.,Bergfort A, Hilal T, Kuropka B, Ilik IA, Weber G, Aktas T, Freund C, Wahl MC Nucleic Acids Res. 2022 Mar 21;50(5):2938-2958. doi: 10.1093/nar/gkac087. PMID:35188580[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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