National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
R00GM132544
United States
Citation
Journal: bioRxiv / Year: 2024 Title: Diverse RNA Structures Induce PRC2 Dimerization and Inhibit Histone Methyltransferase Activity. Authors: Jiarui Song / Liqi Yao / Anne R Gooding / Valentin Thron / Vignesh Kasinath / Thomas R Cech Abstract: Methyltransferase PRC2 (Polycomb Repressive Complex 2) introduces histone H3K27 trimethylation, a repressive chromatin mark, to tune the differential expression of genes. PRC2 is precisely regulated ...Methyltransferase PRC2 (Polycomb Repressive Complex 2) introduces histone H3K27 trimethylation, a repressive chromatin mark, to tune the differential expression of genes. PRC2 is precisely regulated by accessory proteins, histone post-translational modifications and, notably, RNA. Research on PRC2-associated RNA has mostly focused on the tight-binding G-quadruplex (G4) RNAs, which inhibit PRC2 enzymatic activity in vitro and in cells. Our recent cryo-EM structure provided a molecular mechanism for G4 RNA inactivating PRC2 via dimerization, but it remained unclear how diverse RNAs associate with and regulate PRC2. Here, we show that a single-stranded G-rich RNA and an atypical G4 structure called pUG-fold unexpectedly also mediate near-identical PRC2 dimerization resulting in inhibition of PRC2 methyltransferase activity. The conformational flexibility of arginine-rich loops within subunits EZH2 and AEBP2 of PRC2 can accommodate diverse RNA secondary structures, resulting in protein-RNA and protein-protein interfaces similar to those observed previously with G4 RNA. Furthermore, we address a recent report that failed to detect PRC2-associated RNAs in living cells by demonstrating the insensitivity of PRC2-RNA interaction to photochemical crosslinking. Our results support the significance of RNA-mediated PRC2 regulation by showing that this interaction is not limited to a single RNA secondary structure, consistent with the broad PRC2 transcriptome containing many G-tract RNAs incapable of folding into G4 structures.
Name: ZINC ION / type: ligand / ID: 8 / Number of copies: 14 / Formula: ZN
Molecular weight
Theoretical: 65.409 Da
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Experimental details
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Structure determination
Method
cryo EM
Processing
single particle reconstruction
Aggregation state
particle
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Sample preparation
Buffer
pH: 7.9 Details: RNP complex buffer (25 mM HEPES pH 7.9, 50 mM KCl, 2 mM MgCl2, 10% glycerol, and 1 mM TCEP) EM preparation buffer I (25 mM HEPES pH 7.9, 50 mM KCl, 2.5% glycerol, and 1 mM TCEP) EM ...Details: RNP complex buffer (25 mM HEPES pH 7.9, 50 mM KCl, 2 mM MgCl2, 10% glycerol, and 1 mM TCEP) EM preparation buffer I (25 mM HEPES pH 7.9, 50 mM KCl, 2.5% glycerol, and 1 mM TCEP) EM preparation buffer II (25 mM HEPES pH 7.9, 50 mM KCl, 2.5% glycerol, 0.01%NP-40, and 1 mM TCEP).
Vitrification
Cryogen name: ETHANE / Chamber humidity: 90 % / Chamber temperature: 281 K / Instrument: LEICA EM GP / Details: 2-3s of single side blotting.
Details
We used streptavidin-affinity grid preparation method with biotin-labeled RNA at 100 nM concentration. PRC2 was applied in excess at 600 nM.
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Electron microscopy
Microscope
FEI TITAN KRIOS
Specialist optics
Energy filter - Name: TFS Selectris X / Energy filter - Slit width: 10 eV
Image recording
Film or detector model: FEI FALCON IV (4k x 4k) / Number grids imaged: 2 / Number real images: 14230 / Average electron dose: 50.0 e/Å2 Details: Cryo-EM data was collected using a Titan Krios G3i equipped with a Thermo Fisher Falcon 4 direct-electron detector (DED) camera and a Selectris energy filter set with a 10-eV slit width. ...Details: Cryo-EM data was collected using a Titan Krios G3i equipped with a Thermo Fisher Falcon 4 direct-electron detector (DED) camera and a Selectris energy filter set with a 10-eV slit width. Data acquisition was performed using Thermo Fisher EPU at 130,000x magnification (0.97 A/pixel) with a defocus range of minus 1.9 to minus 0.5 micrometer. Movies were collected in EER format with a total dose of 50 electrons per square angstrom and an exposure time of 5.49 s corresponding to 1323 frames.
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Chain - Source name: PDB / Chain - Initial model type: experimental model
Details
Individual PRC2 protomers were built using cryo-EM maps from the multibody refinement. The coordinates of G-quadruplex RNA-bound PRC2 six-subunit complex (PDB: 8FYH) provided a starting model from which all the coordinates were adjusted and rebuilt in the new map using COOT. The model of each PRC2 promoter was subjected to global refinement and minimization in real space using PHENIX. These were then subjected to manual inspection and adjustment in COOT, followed by refinement again in PHENIX. TERRAmut RNA model was generated using a 10-nucleotide single-stranded fragment (UGAGUGUGAG) using AlphaFold3 and then docked into our map for the position we designated as the RNA density.
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Movie
Controller
Open data
Basic information
Map data
Sample
Keywords
Function and homology information
Homo sapiens (human)
Authors
United States, 2 items 
Citation
Structure visualization
Downloads & links
emd_46751.png
http://ftp.pdbj.org/pub/emdb/structures/EMD-46751
Z (Sec.)
Y (Row.)
X (Col.)
Sample components
Trichoplusia ni (cabbage looper)
Processing
Electron microscopy
FIELD EMISSION GUN
