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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.

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