Journal: Nature / Year: 2020 Title: Stress- and ubiquitylation-dependent phase separation of the proteasome. Authors: Sayaka Yasuda / Hikaru Tsuchiya / Ai Kaiho / Qiang Guo / Ken Ikeuchi / Akinori Endo / Naoko Arai / Fumiaki Ohtake / Shigeo Murata / Toshifumi Inada / Wolfgang Baumeister / Rubén Fernández- ...Authors: Sayaka Yasuda / Hikaru Tsuchiya / Ai Kaiho / Qiang Guo / Ken Ikeuchi / Akinori Endo / Naoko Arai / Fumiaki Ohtake / Shigeo Murata / Toshifumi Inada / Wolfgang Baumeister / Rubén Fernández-Busnadiego / Keiji Tanaka / Yasushi Saeki / Abstract: The proteasome is a major proteolytic machine that regulates cellular proteostasis through selective degradation of ubiquitylated proteins. A number of ubiquitin-related molecules have recently been ...The proteasome is a major proteolytic machine that regulates cellular proteostasis through selective degradation of ubiquitylated proteins. A number of ubiquitin-related molecules have recently been found to be involved in the regulation of biomolecular condensates or membraneless organelles, which arise by liquid-liquid phase separation of specific biomolecules, including stress granules, nuclear speckles and autophagosomes, but it remains unclear whether the proteasome also participates in such regulation. Here we reveal that proteasome-containing nuclear foci form under acute hyperosmotic stress. These foci are transient structures that contain ubiquitylated proteins, p97 (also known as valosin-containing protein (VCP)) and multiple proteasome-interacting proteins, which collectively constitute a proteolytic centre. The major substrates for degradation by these foci were ribosomal proteins that failed to properly assemble. Notably, the proteasome foci exhibited properties of liquid droplets. RAD23B, a substrate-shuttling factor for the proteasome, and ubiquitylated proteins were necessary for formation of proteasome foci. In mechanistic terms, a liquid-liquid phase separation was triggered by multivalent interactions of two ubiquitin-associated domains of RAD23B and ubiquitin chains consisting of four or more ubiquitin molecules. Collectively, our results suggest that ubiquitin-chain-dependent phase separation induces the formation of a nuclear proteolytic compartment that promotes proteasomal degradation.
A: 12667.681 Å / B: 12667.681 Å / C: 5130.0 Å α=β=γ: 90.0 °
CCP4 map header:
mode
Image stored as Reals
Å/pix. X/Y/Z
13.680001079914
13.680001079914
13.68
M x/y/z
926
926
375
origin x/y/z
0.000
0.000
0.000
length x/y/z
12667.681
12667.681
5130.000
α/β/γ
90.000
90.000
90.000
MAP C/R/S
1
2
3
start NC/NR/NS
0
0
0
NC/NR/NS
926
926
375
D min/max/mean
-18667.459
6336.026
-0.003
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Supplemental data
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Sample components
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Entire : nuclear region of HCT116 cell, following 0.2M sucrose stimulation
Entire
Name: nuclear region of HCT116 cell, following 0.2M sucrose stimulation
Components
Cell: nuclear region of HCT116 cell, following 0.2M sucrose stimulation
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Supramolecule #1: nuclear region of HCT116 cell, following 0.2M sucrose stimulation
Supramolecule
Name: nuclear region of HCT116 cell, following 0.2M sucrose stimulation type: cell / ID: 1 / Parent: 0
Source (natural)
Organism: Homo sapiens (human)
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Experimental details
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Structure determination
Method
cryo EM
Processing
electron tomography
Aggregation state
cell
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Sample preparation
Buffer
pH: 7
Grid
Model: Quantifoil R2/1 / Material: GOLD / Mesh: 200 / Support film - Material: CARBON / Support film - topology: HOLEY ARRAY
Vitrification
Cryogen name: ETHANE-PROPANE / Instrument: FEI VITROBOT MARK IV
Sectioning
Focused ion beam - Instrument: OTHER / Focused ion beam - Ion: OTHER / Focused ion beam - Voltage: 30 kV / Focused ion beam - Current: 0.01 nA / Focused ion beam - Duration: 1 sec. / Focused ion beam - Temperature: 93 K / Focused ion beam - Initial thickness: 1000 nm / Focused ion beam - Final thickness: 200 nm Focused ion beam - Details: The value given for _emd_sectioning_focused_ion_beam.instrument is Quanta 3D FEG, FEI. This is not in a list of allowed values {'DB235', 'OTHER'} so OTHER is written into the XML file.
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Electron microscopy
Microscope
FEI TITAN KRIOS
Specialist optics
Energy filter - Slit width: 20 eV
Image recording
Film or detector model: GATAN K2 SUMMIT (4k x 4k) / Detector mode: COUNTING / Average electron dose: 1.8 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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