title: RioK1, a new interactor of protein arginine methyltransferase 5 (PRMT5), competes with pICln for binding and modulates PRMT5 complex composition and substrate specificity.
abstract: Protein arginine methylation plays a critical role in differential gene expression through modulating protein-protein and protein-DNA/RNA interactions. Although numerous proteins undergo arginine methylation, only limited information is available on how protein arginine methyltransferases (PRMTs) identify their substrates. The human PRMT5 complex consists of PRMT5, WD45/MEP50 (WD repeat domain 45/methylosome protein 50), and pICln and catalyzes the symmetrical arginine dimethylation of its substrate proteins. pICln recruits the spliceosomal Sm proteins to the PRMT5 complex for methylation, which allows their subsequent loading onto snRNA to form small nuclear ribonucleoproteins. To understand how the PRMT5 complex is regulated, we investigated its biochemical composition and identified RioK1 as a novel, stoichiometric component of the PRMT5 complex. We show that RioK1 and pICln bind to PRMT5 in a mutually exclusive fashion. This results in a PRMT5-WD45/MEP50 core structure that either associates with pICln or RioK1 in distinct complexes. Furthermore, we show that RioK1 functions in analogy to pICln as an adapter protein by recruiting the RNA-binding protein nucleolin to the PRMT5 complex for its symmetrical methylation. The exclusive interaction of PRMT5 with either pICln or RioK1 thus provides the first mechanistic insight into how a methyltransferase can distinguish between its substrate proteins.
authors.affiliation: Department of Biochemistry, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany.
authors.forename: Gernot
authors.initials: G
authors.lastname: Guderian
authors.forename: Christoph
authors.initials: C
authors.lastname: Peter
authors.forename: Julia
authors.initials: J
authors.lastname: Wiesner
authors.forename: Albert
authors.initials: A
authors.lastname: Sickmann
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: Utz
authors.initials: U
authors.lastname: Fischer
authors.forename: Matthias
authors.initials: M
authors.lastname: Grimmler
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D008745:Methylation; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D011496:Protein Methyltransferases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011484:Protein-Arginine N-Methyltransferases; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism; D017381:Spliceosomes / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D014157:Transcription Factors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D007473:Ion Channels; D009097:Multienzyme Complexes; D011496:Protein Methyltransferases; D017346:Protein Serine-Threonine Kinases; D011484:Protein-Arginine N-Methyltransferases; D017411:Ribonucleoproteins, Small Nuclear; C410035:CLNS1A protein, human; C400529:PRMT5 protein, human; C478359:WDR77 protein, human; D014157:Transcription Factors