6ej5
From Proteopedia
A conserved structural element in the RNA helicase UPF1 regulates its catalytic activity in an isoform-specific manner
Structural highlights
Function[RENT1_HUMAN] RNA-dependent helicase and ATPase required for nonsense-mediated decay (NMD) of mRNAs containing premature stop codons. Is recruited to mRNAs upon translation termination and undergoes a cycle of phosphorylation and dephosphorylation; its phosphorylation appears to be a key step in NMD. Recruited by release factors to stalled ribosomes together with the SMG1C protein kinase complex to form the transient SURF (SMG1-UPF1-eRF1-eRF3) complex. In EJC-dependent NMD, the SURF complex associates with the exon junction complex (EJC) (located 50-55 or more nucleotides downstream from the termination codon) through UPF2 and allows the formation of an UPF1-UPF2-UPF3 surveillance complex which is believed to activate NMD. Phosphorylated UPF1 is recognized by EST1B/SMG5, SMG6 and SMG7 which are thought to provide a link to the mRNA degradation machinery involving exonucleolytic and endonucleolytic pathways, and to serve as adapters to protein phosphatase 2A (PP2A), thereby triggering UPF1 dephosphorylation and allowing the recycling of NMD factors. UPF1 can also activate NMD without UPF2 or UPF3, and in the absence of the NMD-enhancing downstream EJC indicative for alternative NMD pathways. Plays a role in replication-dependent histone mRNA degradation at the end of phase S; the function is independent of UPF2. For the recognition of premature termination codons (PTC) and initiation of NMD a competitive interaction between UPF1 and PABPC1 with the ribosome-bound release factors is proposed. The ATPase activity of UPF1 is required for disassembly of mRNPs undergoing NMD. Essential for embryonic viability.[1] [2] [3] [4] [5] Publication Abstract from PubMedThe RNA helicase UPF1 is a key component of the nonsense mediated mRNA decay (NMD) pathway. Previous X-ray crystal structures of UPF1 elucidated the molecular mechanisms of its catalytic activity and regulation. In this study, we examine features of the UPF1 core and identify a structural element that adopts different conformations in the various nucleotide- and RNA-bound states of UPF1. We demonstrate, using biochemical and single molecule assays, that this structural element modulates UPF1 catalytic activity and thereby refer to it as the regulatory loop. Interestingly, there are two alternatively spliced isoforms of UPF1 in mammals which differ only in the lengths of their regulatory loops. The loop in isoform 1 (UPF11) is 11 residues longer than that of isoform 2. We find that this small insertion in UPF11 leads to a two-fold increase in its translocation and ATPase activities. To determine the mechanistic basis of this differential catalytic activity, we have determined the X-ray crystal structure of the helicase core of UPF11 in its apo-state. Our results point toward a novel mechanism of regulation of RNA helicases, wherein alternative splicing leads to subtle structural rearrangements within the protein that are critical to modulate enzyme movements and catalytic activity. A conserved structural element in the RNA helicase UPF1 regulates its catalytic activity in an isoform-specific manner.,Gowravaram M, Bonneau F, Kanaan J, Maciej VD, Fiorini F, Raj S, Croquette V, Le Hir H, Chakrabarti S Nucleic Acids Res. 2018 Jan 25. pii: 4824839. doi: 10.1093/nar/gky040. PMID:29378013[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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