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Structure and function of an effector domain in antiviral factors and tumor suppressors SAMD9 and SAMD9L – pnas.org

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Edited by Ian Wilson, Integrative Structural and Computational Biology, Scripps Research Institute, La Jolla, CA; received September 8, 2021; accepted December 8, 2021
SAMD9 and SAMD9L (SAMD9/9L) are important innate immune defenders against viruses and the development of myeloid tumors. They form a crucial host barrier that poxviruses must overcome for successful infection. A myriad of human diseases including many pediatric myelodysplastic syndromes are caused by mutations in SAMD9/9L. However, the molecular functions of SAMD9/9L and how their functions are executed are unknown, hindering progress in developing effective therapies for SAMD9/9L-associated human diseases. Here, we identified the structure and function of a SAMD9/9L effector domain that is essential for their physiological functions as well as the pathogenic effects exerted by patient-derived mutations. Our study revealed a potential therapeutic target for SAMD9/9L-associated human diseases.
SAMD9 and SAMD9L (SAMD9/9L) are antiviral factors and tumor suppressors, playing a critical role in innate immune defense against poxviruses and the development of myeloid tumors. 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 multidomain 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.
1S.P., X.M., and F.Z. contributed equally.
Author contributions: J.D. and Y.X. designed research; S.P., X.M., F.Z., P.K.P., J. Chaturvedi, J. Coronado, and M.M. performed research; Y.M., S.-B.Q., J.D., and Y.X. analyzed data; and J.D. and Y.X. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2116550119/-/DCSupplemental.
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