Journal: Nat Plants / Year: 2023 Title: Plant-specific features of respiratory supercomplex I + III from Vigna radiata. Authors: M Maldonado / Z Fan / K M Abe / J A Letts / Abstract: The last steps of cellular respiration-an essential metabolic process in plants-are carried out by mitochondrial oxidative phosphorylation. This process involves a chain of multi-subunit membrane ...The last steps of cellular respiration-an essential metabolic process in plants-are carried out by mitochondrial oxidative phosphorylation. This process involves a chain of multi-subunit membrane protein complexes (complexes I-V) that form higher-order assemblies called supercomplexes. Although supercomplexes are the most physiologically relevant form of the oxidative phosphorylation complexes, their functions and structures remain mostly unknown. Here we present the cryogenic electron microscopy structure of the supercomplex I + III from Vigna radiata (mung bean). The structure contains the full subunit complement of complex I, including a newly assigned, plant-specific subunit. It also shows differences in the mitochondrial processing peptidase domain of complex III relative to a previously determined supercomplex with complex IV. The supercomplex interface, while reminiscent of that in other organisms, is plant specific, with a major interface involving complex III's mitochondrial processing peptidase domain and no participation of complex I's bridge domain. The complex I structure suggests that the bridge domain sets the angle between the enzyme's two arms, limiting large-scale conformational changes. Moreover, complex I's catalytic loops and its response in active-to-deactive assays suggest that, in V. radiata, the resting complex adopts a non-canonical state and can sample deactive- or open-like conformations even in the presence of substrate. This study widens our understanding of the possible conformations and behaviour of complex I and supercomplex I + III. Further studies of complex I and its supercomplexes in diverse organisms are needed to determine the universal and clade-specific mechanisms of respiration.
pH: 7.7 Details: 0.2% digitonin, 30 mM HEPES pH 7.7, 150 mM potassium acetate, 1 mM EDTA, 0.002% PMSF
Vitrification
Cryogen name: ETHANE / Chamber humidity: 90 % / Instrument: LEICA EM GP / Details: 4 ul, 20 seconds pre-blot, blot 4 seconds.
Details
Digitonin-extracted, amphipol (A8-35)stabilized
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Electron microscopy
Microscope
TFS GLACIOS
Image recording
Film or detector model: GATAN K3 (6k x 4k) / Number grids imaged: 2 / Number real images: 25712 / Average exposure time: 3.0 sec. / Average electron dose: 60.0 e/Å2
Electron beam
Acceleration voltage: 200 kV / Electron source: FIELD EMISSION GUN
Electron optics
Illumination mode: OTHER / Imaging mode: OTHER / Nominal defocus max: 2.5 µm / Nominal defocus min: 0.5 µm
Sample stage
Cooling holder cryogen: NITROGEN
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Image processing
Final reconstruction
Resolution.type: BY AUTHOR / Resolution: 3.6 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: cryoSPARC / Number images used: 57378
Initial angle assignment
Type: NOT APPLICABLE
Final angle assignment
Type: NOT APPLICABLE
FSC plot (resolution estimation)
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Atomic model buiding 1
Refinement
Space: REAL / Protocol: RIGID BODY FIT
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