Centre National de la Recherche Scientifique (CNRS)
ATIP-Avenir
France
Agence Nationale de la Recherche (ANR)
ANR-18-CE11- 0006-01
France
Agence Nationale de la Recherche (ANR)
ANR-15-IDEX-02
France
Citation
Journal: Nat Commun / Year: 2022 Title: Structure of the human heparan sulfate polymerase complex EXT1-EXT2. Authors: Francisco Leisico / Juneina Omeiri / Christine Le Narvor / Joël Beaudouin / Michael Hons / Daphna Fenel / Guy Schoehn / Yohann Couté / David Bonnaffé / Rabia Sadir / Hugues Lortat-Jacob / Rebekka Wild / Abstract: Heparan sulfates are complex polysaccharides that mediate the interaction with a broad range of protein ligands at the cell surface. A key step in heparan sulfate biosynthesis is catalyzed by the bi- ...Heparan sulfates are complex polysaccharides that mediate the interaction with a broad range of protein ligands at the cell surface. A key step in heparan sulfate biosynthesis is catalyzed by the bi-functional glycosyltransferases EXT1 and EXT2, which generate the glycan backbone consisting of repeating N-acetylglucosamine and glucuronic acid units. The molecular mechanism of heparan sulfate chain polymerization remains, however, unknown. Here, we present the cryo-electron microscopy structure of human EXT1-EXT2, which reveals the formation of a tightly packed hetero-dimeric complex harboring four glycosyltransferase domains. A combination of in vitro and in cellulo mutational studies is used to dissect the functional role of the four catalytic sites. While EXT1 can catalyze both glycosyltransferase reactions, our results indicate that EXT2 might only have N-acetylglucosamine transferase activity. Our findings provide mechanistic insight into heparan sulfate chain elongation as a nonprocessive process and lay the foundation for future studies on EXT1-EXT2 function in health and disease.
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 277 K / Instrument: FEI VITROBOT MARK IV
Details
Purified EXT1-EXT2 complex at 0.4mg/mL was mixed with 1mM of UDP-GlcNAc, 1mM UDP-GlcA and 1mM MnCl2 and incubated 15 min on ice before applying 4 uL of the sample onto a glow discharged Quantifoil holey carbon grid (R1.2/1.3, 300 mesh, copper).
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Electron microscopy
Microscope
FEI TITAN KRIOS
Image recording
Film or detector model: GATAN K3 BIOQUANTUM (6k x 4k) / Average electron dose: 46.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron optics
Illumination mode: OTHER / Imaging mode: BRIGHT FIELD / Nominal defocus max: 3.0 µm / Nominal defocus min: 1.0 µm
Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
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Image processing
Startup model
Type of model: INSILICO MODEL In silico model: Model of the hetero-dimeric EXT1-EXT2 complex predicted using the software AlphaFold2.
Final reconstruction
Resolution.type: BY AUTHOR / Resolution: 2.8 Å / Resolution method: FSC 0.143 CUT-OFF / Number images used: 286390
Initial angle assignment
Type: MAXIMUM LIKELIHOOD
Final angle assignment
Type: MAXIMUM LIKELIHOOD
FSC plot (resolution estimation)
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