Resting mitochondrial complex I from Drosophila melanogaster adopts a helix-locked state

Elife. 2023 Mar 23:12:e84415. doi: 10.7554/eLife.84415.

Abstract

Respiratory complex I is a proton-pumping oxidoreductase key to bioenergetic metabolism. Biochemical studies have found a divide in the behavior of complex I in metazoans that aligns with the evolutionary split between Protostomia and Deuterostomia. Complex I from Deuterostomia including mammals can adopt a biochemically defined off-pathway 'deactive' state, whereas complex I from Protostomia cannot. The presence of off-pathway states complicates the interpretation of structural results and has led to considerable mechanistic debate. Here, we report the structure of mitochondrial complex I from the thoracic muscles of the model protostome Drosophila melanogaster. We show that although D. melanogaster complex I (Dm-CI) does not have a NEM-sensitive deactive state, it does show slow activation kinetics indicative of an off-pathway resting state. The resting-state structure of Dm-CI from the thoracic muscle reveals multiple conformations. We identify a helix-locked state in which an N-terminal α-helix on the NDUFS4 subunit wedges between the peripheral and membrane arms. Comparison of the Dm-CI structure and conformational states to those observed in bacteria, yeast, and mammals provides insight into the roles of subunits across organisms, explains why the Dm-CI off-pathway resting state is NEM insensitive, and raises questions regarding current mechanistic models of complex I turnover.

Keywords: complex I; drosophila melanogaster; electron transport chain; mitochondria; molecular biophysics; respiration; single particle cryoEM; structural biology.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Drosophila melanogaster* / metabolism
  • Electron Transport Complex I* / metabolism
  • Energy Metabolism
  • Mammals / metabolism
  • Mitochondria / metabolism

Substances

  • Electron Transport Complex I