Rieske head domain dynamics and indazole-derivative inhibition of Candida albicans complex III

Structure. 2022 Jan 6;30(1):129-138.e4. doi: 10.1016/j.str.2021.08.006. Epub 2021 Sep 14.


Electron transfer between respiratory complexes drives transmembrane proton translocation, which powers ATP synthesis and membrane transport. The homodimeric respiratory complex III (CIII2) oxidizes ubiquinol to ubiquinone, transferring electrons to cytochrome c and translocating protons through a mechanism known as the Q cycle. The Q cycle involves ubiquinol oxidation and ubiquinone reduction at two different sites within each CIII monomer, as well as movement of the head domain of the Rieske subunit. We determined structures of Candida albicans CIII2 by cryoelectron microscopy (cryo-EM), revealing endogenous ubiquinone and visualizing the continuum of Rieske head domain conformations. Analysis of these conformations does not indicate cooperativity in the Rieske head domain position or ligand binding in the two CIIIs of the CIII2 dimer. Cryo-EM with the indazole derivative Inz-5, which inhibits fungal CIII2 and is fungicidal when administered with fungistatic azole drugs, showed that Inz-5 inhibition alters the equilibrium of Rieske head domain positions.

Keywords: cryo-EM; electron transport chain; three-dimensional variability analysis; ubiquinol:cytochrome c oxidoreductase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Candida albicans / metabolism*
  • Cryoelectron Microscopy
  • Electron Transport
  • Electron Transport Complex III / chemistry*
  • Electron Transport Complex III / metabolism*
  • Fungal Proteins / chemistry
  • Fungal Proteins / metabolism
  • Indazoles / chemistry
  • Indazoles / pharmacology*
  • Models, Molecular
  • Protein Binding
  • Protein Conformation
  • Protein Domains
  • Protein Multimerization
  • Ubiquinone / analogs & derivatives
  • Ubiquinone / chemistry


  • Fungal Proteins
  • Indazoles
  • Ubiquinone
  • Electron Transport Complex III
  • ubiquinol