Cryo-EM structures of engineered active bc1-cbb3 type CIII2CIV super-complexes and electronic communication between the complexes

Stefan Steimle,Dina Schneidman-Duhovny,Merav Braitbard,Yavuz Ozturk,Benjamin A Garcia,Kenji Murakami,Hee Jong Kim,Nur Selamoglu,Fevzi Daldal,Trevor Van Eeuwen

doi:10.1038/s41467-021-21051-4

Stefan Steimle, Dina Schneidman-Duhovny + Show 8 more

Open Access

https://doi.org/10.1038/s41467-021-21051-4

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Abstract

Respiratory electron transport complexes are organized as individual entities or combined as large supercomplexes (SC). Gram-negative bacteria deploy a mitochondrial-like cytochrome (cyt) bc1 (Complex III, CIII2), and may have specific cbb3-type cyt c oxidases (Complex IV, CIV) instead of the canonical aa3-type CIV. Electron transfer between these complexes is mediated by soluble (c2) and membrane-anchored (cy) cyts. Here, we report the structure of an engineered bc1-cbb3 type SC (CIII2CIV, 5.2 Å resolution) and three conformers of native CIII2 (3.3 Å resolution). The SC is active in vivo and in vitro, contains all catalytic subunits and cofactors, and two extra transmembrane helices attributed to cyt cy and the assembly factor CcoH. The cyt cy is integral to SC, its cyt domain is mobile and it conveys electrons to CIV differently than cyt c2. The successful production of a native-like functional SC and determination of its structure illustrate the characteristics of membrane-confined and membrane-external respiratory electron transport pathways in Gram-negative bacteria.

Highlights

Respiratory electron transport complexes are organized as individual entities or combined as large supercomplexes (SC)
Earlier studies have indicated that in R. capsulatus CIII2, CIV, and cyt cy are in close proximity to each other[27]
Similar entities were seen with dodecyl-maltoside or digitonin used to disperse wild-type membrane, but they were of low abundance and unstable, rendering their isolation and study difficult

Summary

Introduction

Respiratory electron transport complexes are organized as individual entities or combined as large supercomplexes (SC). Gram-negative bacteria deploy a mitochondrial-like cytochrome (cyt) bc[1] (Complex III, CIII2), and may have specific cbb3-type cyt c oxidases (Complex IV, CIV) instead of the canonical aa3-type CIV. Electron transfer between these complexes is mediated by soluble (c2) and membrane-anchored (cy) cyts. The successful production of a native-like functional SC and determination of its structure illustrate the characteristics of membrane-confined and membraneexternal respiratory electron transport pathways in Gram-negative bacteria. Complex III (cytochrome (cyt) bc[1] or CIII2) oxidizes QH2 to reduce cyt c, which in turn is oxidized by Complex IV (cyt c oxidase or CIV) converting oxygen to water[1] (Fig. 1a).

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