Unique, Diverged, and Conserved Mitochondrial Functions Influencing Candida albicans Respiration

Abstract

Candida albicans is 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 which C. albicans is 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, NUO3 and NUO4, encode supernumerary subunits of complex I, whereas NUE1 and NUE2 have nonstructural roles in expression of complex I. Similarly, the other three genes have nonstructural roles in expression of complex III (QCE1) or complex IV (COE1 and COE2). In addition to these novel additions, an alternative functional assignment was found for the mitochondrial protein encoded by MNE1. MNE1 was required for complex I expression in C. albicans, whereas the distantly related Saccharomyces cerevisiae ortholog participates in expression of complex III. Phenotypic analysis of deletion mutants showed that fermentative metabolism is unable to support optimal growth rates or yields of C. 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 a Galleria mellonella infection model. The results show that lineage-specific adaptations have occurred in C. albicans mitochondria and highlight the significance of respiratory metabolism in the pathobiology of C. albicans. IMPORTANCE Candida albicans is 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 which C. albicans is 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 in C. albicans metabolism.

Mitochondria-Mediated Azole Drug Resistance and Fungal Pathogenicity: Opportunities for Therapeutic Development

“…Recently, a study identified seven genes ( Nuo3 , Nuo4 , Nue1 , Nue2 , Qce1 , Coe1 , and Coe2 ) that are unique to the CTG fungal clade, which is so named because they generally translate CTG as serine rather than leucine. The CTG fungal clade contains multiple important human pathogens, including C. albicans , and showed that they are required for full mitochondrial respiratory metabolism and fungal virulence [ 13 ], implying that these clade-specific mitochondrial factors might represent novel antifungal therapeutic targets. The mitochondrial respiratory chain is composed of four large multi-subunit enzymes, complexes I to IV.…”

“…Loss of these proteins can lead to deficiencies in respiration and virulence [ 21 , 72 ]. Similarly, deletion of Nue1 , Nue2 , Nuo3 , or Nuo4 can impair complex I function, causing deficiencies in respiration and virulence [ 13 ], making them attractive antifungal drug targets. Additionally, dysfunction of complex I can lead to ROS accumulation in mitochondria, which in turn promotes fungal cell death [ 76 ].…”

“…Azole drug resistance and the fungal virulence are intimately intertwined with their metabolism, and mitochondria play a central role in that metabolism [ 12 , 13 ]. Mitochondria house and integrate multiple metabolic functions relating to lipids, iron metabolism, energy production, and cell wall biosynthesis [ 14 , 15 , 16 , 17 , 18 , 19 ], which are associated with fungal virulence and resistance to azoles.…”

An evolutionarily diverged mitochondrial protein controls biofilm growth and virulence inCandida albicans

“…It is well known that the integrity and function of mitochondria are essential to the virulence of C. albicans. Mutations affecting any one of a number of mitochondrial functions, including mitochondrial ribosome synthesis, mitochondrial transcription or genome maintenance, protein import, or functioning of the electron transport chain (ETC), result in C. albicans virulence defect (12,26,27,33,34).…”

“…The fact that orf19.2500 mutant could not grow on alternative carbon sources indicated a respiratory defect likely due to a faulty electron transport chain (12). To test this hypothesis, we carried out Seahorse assays to test the respiratory prowess of the isolated mitochondria of the mutant strain, in the presence of Complex I (CI) substrates (pyruvate + malate) ( Fig 3B).…”