Journal: Nat Struct Mol Biol / Year: 2024 Title: SCAF1 drives the compositional diversity of mammalian respirasomes. Authors: Irene Vercellino / Leonid A Sazanov / Abstract: Supercomplexes of the respiratory chain are established constituents of the oxidative phosphorylation system, but their role in mammalian metabolism has been hotly debated. Although recent studies ...Supercomplexes of the respiratory chain are established constituents of the oxidative phosphorylation system, but their role in mammalian metabolism has been hotly debated. Although recent studies have shown that different tissues/organs are equipped with specific sets of supercomplexes, depending on their metabolic needs, the notion that supercomplexes have a role in the regulation of metabolism has been challenged. However, irrespective of the mechanistic conclusions, the composition of various high molecular weight supercomplexes remains uncertain. Here, using cryogenic electron microscopy, we demonstrate that mammalian (mouse) tissues contain three defined types of 'respirasome', supercomplexes made of CI, CIII and CIV. The stoichiometry and position of CIV differs in the three respirasomes, of which only one contains the supercomplex-associated factor SCAF1, whose involvement in respirasome formation has long been contended. Our structures confirm that the 'canonical' respirasome (the C-respirasome, CICIIICIV) does not contain SCAF1, which is instead associated to a different respirasome (the CS-respirasome), containing a second copy of CIV. We also identify an alternative respirasome (A-respirasome), with CIV bound to the 'back' of CI, instead of the 'toe'. This structural characterization of mouse mitochondrial supercomplexes allows us to hypothesize a mechanistic basis for their specific role in different metabolic conditions.
Film or detector model: GATAN K3 BIOQUANTUM (6k x 4k) / Number grids imaged: 1 / Number real images: 9453 / Average exposure time: 4.4 sec. / Average electron dose: 80.0 e/Å2
Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
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Image processing
Particle selection
Number selected: 1758187
Startup model
Type of model: OTHER Details: map obtained from previous processing of test dataset
Initial angle assignment
Type: MAXIMUM LIKELIHOOD
Final 3D classification
Number classes: 4
Final angle assignment
Type: MAXIMUM LIKELIHOOD
Final reconstruction
Number classes used: 1 / Algorithm: FOURIER SPACE / Resolution.type: BY AUTHOR / Resolution: 3.2 Å / Resolution method: FSC 0.143 CUT-OFF / Number images used: 51488
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