Mitochondrial targeting of intact CYP2B1 and CYP2E1 and N‐terminal truncated CYP1A1 proteins in Saccharomyces cerevisiae − role of protein kinase A in the mitochondrial targeting of CYP2E1

Previously we showed that intact rat cytochrome P450 2E1, cytochrome P450 2B1 and truncated cytochrome P450 1A1 are targeted to mitochondria in rat tissues and COS cells. However, some reports suggest that truncated cytochrome P450 2E1 is targeted to mitochondria. In this study, we used a heterologous yeast system to ascertain the conservation of targeting mechanisms and the nature of mitochondria‐targeted proteins. Mitochondrial integrity and purity were established using electron microscopy, and treatment with digitonin and protease. Full‐length cytochrome P450 2E1 and cytochrome P450 2B1 were targeted both to microsomes and mitochondria, whereas truncated cytochrome P450 1A1 (+ 5 and + 33/cytochrome P450 1A1) were targeted to mitochondria. Inability to target intact cytochrome P450 1A1 was probably due to lack of cytosolic endoprotease activity in yeast cells. Mitochondrial targeting of cytochrome P450 2E1 was severely impaired in protein kinase A‐deficient cells. Similarly, a phosphorylation site mutant cytochrome P450 2E1 (Ser129A) was poorly targeted to the mitochondria, thus confirming the importance of protein kinase A‐mediated protein phosphorylation in mitochondrial targeting. Mitochondria‐targeted proteins were localized in the matrix compartment peripherally associated with the inner membrane and their ethoxyresorufin O‐dealkylation, erythromycin N‐demethylase, benzoxyresorufin O‐dealkylation and nitrosodimethylamine N‐demethylase activities were fully supported by yeast mitochondrial ferredoxin and ferredoxin reductase.