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Human SAMD9 is a Poxvirus-Activatable Anticodon Nuclease Inhibiting Codon-Specific Protein Synthesis

ABSTRACT: As a defense strategy against viruses or competitors, some microbes employ anticodon nucleases (ACNases) to deplete essential tRNAs, effectively halting global protein synthesis. However, this mechanism has not been observed in multicellular eukaryotes. Here, we report that human SAMD9 is an ACNase that specifically cleaves phenylalanine tRNA (tRNAPhe), resulting in codon-specific ribosomal pausing and stress signaling. While SAMD9 ACNase activity is normally latent in cells, it can be activated by poxvirus infection or rendered constitutively active by SAMD9 mutations associated with various human disorders, revealing tRNAPhe depletion as an antiviral mechanism and a pathogenic condition in SAMD9 disorders. We identified the N-terminal effector domain of SAMD9 as the ACNase, with substrate specificity primarily determined by a eukaryotic tRNAPhe-specific 2’-O-methylation at the wobble position, making virtually all eukaryotic tRNAPhe susceptible to SAMD9 cleavage. Notably, the structure and substrate specificity of SAMD9 ACNase differ from known microbial ACNases, suggesting convergent evolution of a common immune defense strategy targeting tRNAs.

ORGANISM(S): Homo sapiens

PROVIDER: GSE229979 | GEO | 2023/06/07

REPOSITORIES: GEO

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Human SAMD9 is a Virus-Activatable Anticodon Nuclease Inhibiting Codon-Specific Protein Synthesis

Project description:Transfer RNAs (tRNAs) are one of the most conserved components of protein synthesis machinery. An effective strategy for microbes to defend against viruses or competitors is to employ anticodon nucleases (ACNases) to deplete essential tRNAs and thereby shut off global protein synthesis, but this strategy has not been observed in multicellular eukaryotes. Here, we report that human SAMD9 is a virus-activatable ACNase that specifically depletes phenylalanine tRNA (tRNAPhe), causing codon-specific ribosomal pausing and inducing stress signaling. SAMD9 ACNase can be activated by poxvirus infection or by SAMD9 mutations associated with a spectrum of developmental or immunological disorders, implicating tRNAPhe deficiency as a major toxic effect in these human diseases and suggesting a new therapeutic strategy. The specificity of the ACNase, located to an N-terminal effector domain of SAMD9, is largely determined by a eukaryotic tRNAPhe specific 2’-O-methylation at the wobble position, making eukaryotic tRNAPhe a universal but specific target for SAMD9. The SAMD9 ACNase differs from the microbial ACNases in structure and substrate specificity, suggesting convergent evolution resulted in a universal immune defense strategy targeting tRNAs.

2023-06-07 | GSE230043 | GEO

Structure and Function of an Effector Domain in Antiviral Factors and Tumor Suppressors SAMD9 and SAMD9L

Project description:SAMD9 and SAMD9L (SAMD9/9L) are antiviral factors and myeloid tumor suppressors. They are critical for innate immune defense against several viruses, particularly the poxviruses. SAMD9/9L mutations with a gain-of-function (GoF) in inhibiting cell growth cause multisystem developmental disorders including many pediatric myelodysplastic syndromes. Predicted to be multi-domain proteins with an architecture like that of the NOD-like receptors, SAMD9/9L molecular functions and domain structures are largely unknown. Here, we identified a SAMD9/9L effector domain that functions by binding to double-stranded nucleic acids (dsNA) and determined the crystal structure of the domain in complex with DNA. Aided with precise mutations that differentially perturb dsNA binding, we demonstrated that the antiviral and antiproliferative functions of the wild-type and GoF SAMD9/9L variants rely on dsNA binding by the effector domain. Furthermore, we showed that GoF variants inhibit global protein synthesis, reduce translation elongation, and induce proteotoxic stress response, which all require dsNA binding by the effector domain. The identification of the structure and function of a SAMD9/9L effector domain provides a therapeutic target for SAMD9/9L associated human diseases.

2022-01-19 | GSE186456 | GEO

Loss of a Conserved tRNA Anticodon Modification Perturbs Cellular Signaling

Project description:Transfer RNA (tRNA) modifications enhance the efficiency, specificity and fidelity of translation in all organisms. The anticodon modification mcm5s2U34 is required for normal growth and stress resistance in yeast; mutants lacking this modification have numerous phenotypes. Mutations in the homologous human genes are linked to neurological disease. The yeast phenotypes can be ameliorated by overexpression of specific tRNAs, suggesting that the modifications are necessary for efficient translation of specific codons. We determined the in vivo ribosome distributions at single codon resolution in yeast strains lacking mcm5s2U. We found accumulations at AAA, CAA, and GAA codons, suggesting that translation is slow when these codons are in the ribosomal A site, but these changes appeared too small to affect protein output. Instead, we observed activation of the GCN4-mediated stress response by a non- canonical pathway. Thus, loss of mcm5s2U causes global effects on gene expression due to perturbation of cellular signaling. WT yeast and mutants lacking anticodon tRNA modifications were grown in YPD, and subjected to ribosome footprint profiling (ribo-seq) and RNA-seq of poly-A selected RNA. Dataset contains biological replicates for WT, Δncs6 and Δuba4. Technical replicates were also performed for all RNA-seq datasets (using a different poly-A selection method).

2013-08-01 | E-GEOD-45366 | biostudies-arrayexpress

Loss of a Conserved tRNA Anticodon Modification Perturbs Cellular Signaling

2013-08-01 | GSE45366 | GEO

Mechanism of translation inhibition by type II GNAT toxins: AtaT, TacT, and ItaT

Project description:Type II toxin-antitoxin (TA) systems are two-gene modules widely distributed among prokaryotes. GNAT toxins associated with the DUF1778 antitoxins represent a large family of type II TAs. GNAT toxins inhibit cell growth by disrupting translation via acetylation of aminoacyl-tRNAs. Using ribosome profiling, we investigated the in vivo substrate specificity of three GNAT toxins: AtaT2, TacT3, and ItaT.

2020-06-17 | GSE148424 | GEO

The RNA methyltransferase METTL8 installs m3C32 in mitochondrial tRNAsThr/Ser(UCN) to optimise tRNA structure and mitochondrial translation

Project description:Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here, we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinations for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.

2021-12-04 | GSE185015 | GEO

The RNA methyltransferase METTL8 installs m3C32 in mitochondrial tRNAsThr/Ser(UCN) to optimise tRNA structure and mitochondrial translation

2021-12-04 | GSE174448 | GEO

Quantifying mistranslation from alanine tRNA anticodon variants in S. cerevisiae

Project description:Transfer RNAs (tRNAs) maintain translational fidelity through strict charging by their cognate aminoacyl-tRNA synthetase and codon:anticodon base pairing with the mRNA at the ribosome. Mistranslation occurs when an amino acid not specified by the genetic code is incorporated into a protein. Since alanyl-tRNA synthetase uniquely recognizes a G3:U70 base pair in alanine tRNAs and the anticodon plays no role in charging, alanine tRNA variants with anticodon mutations have the potential to mistranslate alanine. Our goal was to quantify mis-incorporation of alanine into proteins in Saccharomyces cerevisiae strains expressing one of 57 different alanine tRNA anticodon variants. Using mass spectrometry, we observed mistranslation for 45 of the variants when expressed on single-copy plasmids.

2023-10-02 | PXD038242 | Pride

Identification of SAMD9 and SAMD9L interactome in HEK293T cells

Project description:Recently, heterozygous germline mutations were identified in sterile alpha motif (SAM) domain-9 (SAMD9) and its paralog, SAMD9-like (SAMD9L) in children with monosomy 7 mediated MDS. Expression of SAMD9 and SAMD9L is induced by interferons and other inflammatory stimuli and causes reduced cell division and cell growth and most pathogenic mutations found in patients dramatically enhance these effects. The goal of this project is to identify the interactome of SAMD9 and SAMD9L to better understand their role in cell cycle and proliferation regulation

2021-03-24 | PXD020018 | Pride

Human tRNAs with inosine 34 are essential to efficiently translate eukarya-specific low-complexity proteins

Project description:The modification of adenosine to inosine at the wobble position (I34) of tRNA anticodons is an abundant and essential feature of eukaryotic tRNAs. The expansion of inosine-containing tRNAs in eukaryotes followed the transformation of the homodimeric bacterial enzyme TadA, which generates I34 in tRNAArg and tRNALeu, into the heterodimeric eukaryotic enzyme ADAT, which modifies up to eight different tRNAs. The emergence of ADAT and its larger set of substrates, strongly influenced the tRNA composition and codon usage of eukaryotic genomes. However, the selective advantages that drove the expansion of I34-tRNAs remain unknown. Here we investigate the functional relevance of I34-tRNAs in human cells and show that a full complement of these tRNAs is necessary for the translation of low-complexity protein domains enriched in amino acids cognate for I34-tRNAs. The coding sequences for these domains require codons translated by I34-tRNAs, in detriment of synonymous codons that use other tRNAs. I34-tRNA-dependent low-complexity proteins are enriched in functional categories related to cell adhesion, and depletion in I34-tRNAs leads to cellular phenotypes consistent with these roles. We show that the distribution of these low-complexity proteins mirrors the distribution of I34-tRNAs in the phylogenetic tree.

2021-09-10 | PXD025024 | Pride

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