Mitochondrial P450 redox partners

The redox partners of mitochondrial P450s are adrenodoxin reductase (AdR), an NADPH-dependent FAD flavoprotein and adrenodoxin (Adx), a [2Fe-2S] ferredoxin-type iron sulfur protein. These are named for the two redox partners of mammalian adrenal mitochondrial P450s, and this designation has been liberally bestowed on proteins from animals that don't have adrenals. AdR is associated to the inner membrane of mitochondria and Adx is a soluble protein of the mitochondrial matrix.

The bovine orthologs of Adx and AdR are capable of supporting the activity of an insect mitochondrial P450, house fly CYP12A1 (Guzov et al., 1998). The reduction of CYP12A1 is rapid and efficient with bovine adrenodoxin reductase / adrenodoxin while under the same conditions house fly microsomal P450 reductase is only marginally effective.

There is one adrenodoxin ortholog in insect genomes. The Drosophila adrenodoxin ortholog (CG1319) is a 152 amino acid protein, 61% identical to the bovine protein.

Insect genomes also carry a single adrenodoxin reductase ortholog. The Drosophila P-element induced mutant dare1 for defective in the avoidance of repellents was found to encode Drosophila adrenodoxin reductase (Freeman et al., 1999). Strong dare mutants undergo developmental arrest, and this phenotype is largely rescued by feeding 20-hydroxyecdysone. Decreasing by half the wild type expression of dare blocks the olfactory response. The gene is expressed at low levels in all tissues of the adult fly, including the brain and the antennae. Highest expression is found in the prothoracic gland portion of the ring gland of third instar larvae, as well as in the nurse cells of adult ovaries. These tissues are known to require mitochondrial P450s (CYP302A1, CYP315A1) for ecdysteroid production. The 55KDa protein encoded by dare is 42% identical to the human enzyme.

Shi et al. (2022) functionally expressed Helicoverpa armigera Adx and AdR in Sf9 cells and showed that these redox partners supported the activity of five mito clan P450s (CYP333B3, CYP301B1, CYP339A1, CYP302A1 and CYP315A1). These authors also compared the sequences of these redox partners in nine insect species with the sequences of bovine and human Adx and AdR, and highlighted conserved motifs in both redox partners.