National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
F31 GM131648
United States
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
R35 GM126982
United States
Howard Hughes Medical Institute (HHMI)
United States
Citation
Journal: J Biol Chem / Year: 2023 Title: Structural insight into G-protein chaperone-mediated maturation of a bacterial adenosylcobalamin-dependent mutase. Authors: Francesca A Vaccaro / Daphne A Faber / Gisele A Andree / David A Born / Gyunghoon Kang / Dallas R Fonseca / Marco Jost / Catherine L Drennan / Abstract: G-protein metallochaperones are essential for the proper maturation of numerous metalloenzymes. The G-protein chaperone MMAA in humans (MeaB in bacteria) uses GTP hydrolysis to facilitate the ...G-protein metallochaperones are essential for the proper maturation of numerous metalloenzymes. The G-protein chaperone MMAA in humans (MeaB in bacteria) uses GTP hydrolysis to facilitate the delivery of adenosylcobalamin (AdoCbl) to AdoCbl-dependent methylmalonyl-CoA mutase, an essential metabolic enzyme. This G-protein chaperone also facilitates the removal of damaged cobalamin (Cbl) for repair. Although most chaperones are standalone proteins, isobutyryl-CoA mutase fused (IcmF) has a G-protein domain covalently attached to its target mutase. We previously showed that dimeric MeaB undergoes a 180° rotation to reach a state capable of GTP hydrolysis (an active G-protein state), in which so-called switch III residues of one protomer contact the G-nucleotide of the other protomer. However, it was unclear whether other G-protein chaperones also adopted this conformation. Here, we show that the G-protein domain in a fused system forms a similar active conformation, requiring IcmF oligomerization. IcmF oligomerizes both upon Cbl damage and in the presence of the nonhydrolyzable GTP analog, guanosine-5'-[(β,γ)-methyleno]triphosphate, forming supramolecular complexes observable by mass photometry and EM. Cryo-EM structural analysis reveals that the second protomer of the G-protein intermolecular dimer props open the mutase active site using residues of switch III as a wedge, allowing for AdoCbl insertion or damaged Cbl removal. With the series of structural snapshots now available, we now describe here the molecular basis of G-protein-assisted AdoCbl-dependent mutase maturation, explaining how GTP binding prepares a mutase for cofactor delivery and how GTP hydrolysis allows the mutase to capture the cofactor.
Name: MAGNESIUM ION / type: ligand / ID: 3 / Number of copies: 1 / Formula: MG
Molecular weight
Theoretical: 24.305 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
Concentration
0.25 mg/mL
Buffer
pH: 8 Details: 20 mM HEPES pH 8, 50 mM NaCl, 500 mM GTP, 500 mM MgCl2
Grid
Model: Quantifoil R1.2/1.3 / Material: COPPER / Mesh: 300 / Support film - Material: CARBON / Support film - topology: HOLEY / Pretreatment - Type: GLOW DISCHARGE / Pretreatment - Time: 60 sec. / Pretreatment - Pressure: 3.9 kPa
Vitrification
Cryogen name: ETHANE / Chamber humidity: 95 % / Chamber temperature: 281.15 K / Instrument: FEI VITROBOT MARK IV / Details: Blot for 3s.
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Electron microscopy
Microscope
FEI TALOS ARCTICA
Image recording
Film or detector model: FEI FALCON III (4k x 4k) / Number grids imaged: 1 / Number real images: 673 / Average exposure time: 3.99 sec. / Average electron dose: 58.71 e/Å2
Electron beam
Acceleration voltage: 200 kV / Electron source: FIELD EMISSION GUN
Chain - Chain ID: B / Chain - Residue range: 22-1093 / Chain - Source name: PDB / Chain - Initial model type: experimental model Details: Docked the model as two different fragments: resi 22-442 and resi 443-1093
Refinement
Protocol: RIGID BODY FIT
Output model
PDB-8ssl: Isobutyryl-CoA mutase fused Q341A in the presence of GTP
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