Abstract
Nonsense-mediated mRNA decay (NMD) targets premature stop codon (PTC)-containing mRNAs for rapid degradation, and is essential for mammalian embryonic development, brain development and modulation of the stress response. The key event in NMD is the SMG1-mediated phosphorylation of an RNA helicase UPF1 and SMG1 kinase activity is inhibited by SMG8 and SMG9 in an unknown mechanism. Here, we determined the cryo-EM structures of human SMG1 at 3.6 Å resolution and the SMG1–SMG8–SMG9 complex at 3.4 Å resolution, respectively. SMG8 has a C-terminal kinase inhibitory domain (KID), which covers the catalytic pocket and inhibits the kinase activity of SMG1. Structural analyses suggest that GTP hydrolysis of SMG9 would lead to a dramatic conformational change of SMG8–SMG9 and the KID would move away from the inhibitory position to restore SMG1 kinase activity. Thus, our structural and biochemical analyses provide a mechanistic understanding of SMG1–SMG8–SMG9 complex assembly and the regulatory mechanism of SMG1 kinase activity.
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Acknowledgements
We thank Center of Cryo-Electron Microscopy, Zhejiang University School of Medicine, Center for Biological Imaging of Institute of Biophysics of Chinese Academy of Sciences, and National Center for Protein Science Shanghai for the supports on cryo-EM data collection and data analyses. We thank the Biomedical Core Facility, Fudan University for the supports on Mass Spectrometry analyses. This work was supported by the National key R&D program of China (2016YFA0500700), the National Natural Science Foundation of China (31830107, 31821002, 31425008), the National Ten-Thousand Talent Program (Y.X.), the National Program for support of Top-Notch Young Professionals (Y.X.), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB08000000).
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L.Z., L.L., Y.Q., and Y.X. designed the experiments. L.Z. purified the proteins and performed biochemical analyses. Y.Q. prepared the cryo-EM sample, collected the data and determined the structure. Y.Q. and L.L. built the structural model. L.Z., L.L., Y.Q., and Y. X. analyzed the data and wrote the manuscript. Y.X. supervised the project.
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Zhu, L., Li, L., Qi, Y. et al. Cryo-EM structure of SMG1–SMG8–SMG9 complex. Cell Res 29, 1027–1034 (2019). https://doi.org/10.1038/s41422-019-0255-3
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DOI: https://doi.org/10.1038/s41422-019-0255-3
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