1. Molecular basis of TMED9 oligomerization and entrapment of misfolded protein cargo in the early secretory pathway.
- Author
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Le Xiao, Xiong Pi, Goss, Alissa C., El-Baba, Tarick, Ehrmann, Julian F., Grinkevich, Elizabeth, Bazua-Valenti, Silvana, Padovano, Valeria, Alper, Seth L., Carey, Dominique, Udeshi, Namrata D., Carr, Steven A., Lorenzo Pablo, Juan, Robinson, Carol V., Greka, Anna, and Hao Wu
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TRANSMEMBRANE domains , *CYTOTOXINS , *FREIGHT & freightage , *OLIGOMERIZATION , *MUCINS - Abstract
Intracellular accumulation of misfolded proteins causes serious human proteinopathies. The transmembrane emp24 domain 9 (TMED9) cargo receptor promotes a general mechanism of cytotoxicity by entrapping misfolded protein cargos in the early secretory pathway. However, the molecular basis for this TMED9-mediated cargo retention remains elusive. Here, we report cryo-electron microscopy structures of TMED9, which reveal its unexpected self-oligomerization into octamers, dodecamers, and, by extension, even higher-order oligomers. The TMED9 oligomerization is driven by an intrinsic symmetry mismatch between the trimeric coiled coil domain and the tetrameric transmembrane domain. Using frameshifted Mucin 1 as an example of aggregated disease-related protein cargo, we implicate a mode of direct interaction with the TMED9 luminal Golgi-dynamics domain. The structures suggest and we confirm that TMED9 oligomerization favors the recruitment of coat protein I (COPI), but not COPII coatomers, facilitating retrograde transport and explaining the observed cargo entrapment. Our work thus reveals a molecular basis for TMED9-mediated misfolded protein retention in the early secretory pathway. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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