National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
DP2GM137412
United States
Citation
Journal: J Cell Biol / Year: 2023 Title: A selectivity filter in the ER membrane protein complex limits protein misinsertion at the ER. Authors: Tino Pleiner / Masami Hazu / Giovani Pinton Tomaleri / Vy N Nguyen / Kurt Januszyk / Rebecca M Voorhees / Abstract: Tail-anchored (TA) proteins play essential roles in mammalian cells, and their accurate localization is critical for proteostasis. Biophysical similarities lead to mistargeting of mitochondrial TA ...Tail-anchored (TA) proteins play essential roles in mammalian cells, and their accurate localization is critical for proteostasis. Biophysical similarities lead to mistargeting of mitochondrial TA proteins to the ER, where they are delivered to the insertase, the ER membrane protein complex (EMC). Leveraging an improved structural model of the human EMC, we used mutagenesis and site-specific crosslinking to map the path of a TA protein from its cytosolic capture by methionine-rich loops to its membrane insertion through a hydrophilic vestibule. Positively charged residues at the entrance to the vestibule function as a selectivity filter that uses charge-repulsion to reject mitochondrial TA proteins. Similarly, this selectivity filter retains the positively charged soluble domains of multipass substrates in the cytosol, thereby ensuring they adopt the correct topology and enforcing the "positive-inside" rule. Substrate discrimination by the EMC provides a biochemical explanation for one role of charge in TA protein sorting and protects compartment integrity by limiting protein misinsertion.
Cryogen name: ETHANE / Chamber humidity: 95 % / Chamber temperature: 279 K / Instrument: FEI VITROBOT MARK IV
Details
Sample solubilized and purified in GDN
-
Electron microscopy
Microscope
FEI TITAN KRIOS
Specialist optics
Energy filter - Name: GIF Quantum LS / Energy filter - Slit width: 20 eV
Image recording
Film or detector model: GATAN K3 (6k x 4k) / Number grids imaged: 2 / Number real images: 11822 / Average exposure time: 2.66 sec. / Average electron dose: 60.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron optics
Illumination mode: SPOT SCAN / Imaging mode: DARK FIELD / Cs: 2.7 mm / Nominal defocus max: 3.0 µm / Nominal defocus min: 1.0 µm / Nominal magnification: 130000
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