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

During cellular respiration, electron transfer between the integral membrane protein complexes of the electron transport chain is coupled to proton translocation across the inner mitochondrial membrane, which in turn powers synthesis of ATP and transmembrane transport processes. The homodimeric electron transport chain Complex III (CIII2) oxidizes ubiquinol (UQH2) to ubiquinone (UQ), transferring electrons to cytochrome c, and translocating protons through a mechanism known as the Q cycle. The Q cycle involves UQH2 oxidation and UQ reduction at two different sites within each CIII monomer, as well as movement of the head domain of the Rieske subunit. We used cryoEM to determine the structure of CIII2 from Candida albicans, revealing density for endogenous UQ in the structure and allowing us to directly visualize the continuum of conformations of the Rieske head domain. Analysis of these conformations does not indicate cooperativity in the position of the Rieske head domains or binding of ligands in the two CIIIs of the CIII2 dimer. CryoEM with the indazole derivative Inz-5, which inhibits fungal CIII2 and is fungicidal when administered with fungistatic azole drugs, showed that inhibition by Inz-5 alters the equilibrium of the Rieske head domain positions.

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Unique, Diverged, and Conserved Mitochondrial Functions InfluencingCandida albicansRespiration

mBio ◽

10.1128/mbio.00300-19 ◽

2019 ◽

Vol 10 (3) ◽

Cited By ~ 9

Author(s):

Nuo Sun ◽

Rebecca S. Parrish ◽

Richard A. Calderone ◽

William A. Fonzi

Keyword(s):

Candida Albicans ◽

Fungal Pathogen ◽

Complex I ◽

Electron Transport Chain ◽

Complex Iii ◽

Respiratory Metabolism ◽

Content Type ◽

Transport Chain ◽

Opportunistic Fungal Pathogen ◽

Lineage Specific Genes

ABSTRACTCandida albicansis an opportunistic fungal pathogen of major clinical concern. The virulence of this pathogen is intimately intertwined with its metabolism. Mitochondria, which have a central metabolic role, have undergone many lineage-specific adaptations in association with their eukaryotic host. A screen for lineage-specific genes identified seven such genes specific to the CTG clade of fungi, of whichC. albicansis a member. Each is required for respiratory growth and is integral to expression of complex I, III, or IV of the electron transport chain. Two genes,NUO3andNUO4, encode supernumerary subunits of complex I, whereasNUE1andNUE2have nonstructural roles in expression of complex I. Similarly, the other three genes have nonstructural roles in expression of complex III (QCE1) or complex IV (COE1andCOE2). In addition to these novel additions, an alternative functional assignment was found for the mitochondrial protein encoded byMNE1.MNE1was required for complex I expression inC. albicans, whereas the distantly relatedSaccharomyces cerevisiaeortholog participates in expression of complex III. Phenotypic analysis of deletion mutants showed that fermentative metabolism is unable to support optimal growth rates or yields ofC. albicans. However, yeast-hypha morphogenesis, an important virulence attribute, did not require respiratory metabolism under hypoxic conditions. The inability to respire also resulted in hypersensitivity to the antifungal fluconazole and in attenuated virulence in aGalleria mellonellainfection model. The results show that lineage-specific adaptations have occurred inC. albicansmitochondria and highlight the significance of respiratory metabolism in the pathobiology ofC. albicans.IMPORTANCECandida albicansis an opportunistic fungal pathogen of major clinical concern. The virulence of this pathogen is intimately intertwined with its metabolic behavior, and mitochondria have a central role in that metabolism. Mitochondria have undergone many evolutionary changes, which include lineage-specific adaptations in association with their eukaryotic host. Seven lineage-specific genes required for electron transport chain function were identified in the CTG clade of fungi, of whichC. albicansis a member. Additionally, examination of several highly diverged orthologs encoding mitochondrial proteins demonstrated functional reassignment for one of these. Deficits imparted by deletion of these genes revealed the critical role of respiration in virulence attributes of the fungus and highlight important evolutionary adaptations inC. albicansmetabolism.

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