Journal: Proc Natl Acad Sci U S A / Year: 2023 Title: A linker protein from a red-type pyrenoid phase separates with Rubisco via oligomerizing sticker motifs. Authors: Zhen Guo Oh / Warren Shou Leong Ang / Cheng Wei Poh / Soak-Kuan Lai / Siu Kwan Sze / Hoi-Yeung Li / Shashi Bhushan / Tobias Wunder / Oliver Mueller-Cajar / Abstract: The slow kinetics and poor substrate specificity of the key photosynthetic CO-fixing enzyme Rubisco have prompted the repeated evolution of Rubisco-containing biomolecular condensates known as ...The slow kinetics and poor substrate specificity of the key photosynthetic CO-fixing enzyme Rubisco have prompted the repeated evolution of Rubisco-containing biomolecular condensates known as pyrenoids in the majority of eukaryotic microalgae. Diatoms dominate marine photosynthesis, but the interactions underlying their pyrenoids are unknown. Here, we identify and characterize the Rubisco linker protein PYCO1 from . PYCO1 is a tandem repeat protein containing prion-like domains that localizes to the pyrenoid. It undergoes homotypic liquid-liquid phase separation (LLPS) to form condensates that specifically partition diatom Rubisco. Saturation of PYCO1 condensates with Rubisco greatly reduces the mobility of droplet components. Cryo-electron microscopy and mutagenesis data revealed the sticker motifs required for homotypic and heterotypic phase separation. Our data indicate that the PYCO1-Rubisco network is cross-linked by PYCO1 stickers that oligomerize to bind to the small subunits lining the central solvent channel of the Rubisco holoenzyme. A second sticker motif binds to the large subunit. Pyrenoidal Rubisco condensates are highly diverse and tractable models of functional LLPS.
Model: Quantifoil R2/2 / Material: COPPER / Mesh: 200 / Support film - Material: CARBON / Support film - topology: HOLEY / Support film - Film thickness: 2 / Pretreatment - Type: GLOW DISCHARGE / Pretreatment - Time: 20 sec. / Pretreatment - Atmosphere: AIR / Pretreatment - Pressure: 0.6 kPa
Vitrification
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 277 K / Instrument: FEI VITROBOT MARK IV / Details: Blotted for 2 sec with blot force of 1..
Details
0.5 mg/mL Rubisco incubated with 21.9 uM of PYCO1(452-592).
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Electron microscopy
Microscope
FEI TITAN KRIOS
Specialist optics
Energy filter - Name: GIF Bioquantum / Energy filter - Slit width: 20 eV / Details: Gatan EF
Image recording
Film or detector model: GATAN K3 (6k x 4k) / Digitization - Dimensions - Width: 5760 pixel / Digitization - Dimensions - Height: 4092 pixel / Number grids imaged: 1 / Number real images: 8861 / Average exposure time: 5.0 sec. / Average electron dose: 65.0 e/Å2 Details: Images were collected in movie mode at 10 frames per second.
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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