ABSTRACT
In mammals, cytosolic phospholipases A2 (cPLA2s) play important physiological roles by releasing arachidonic acid, a precursor for bioactive lipid mediators, from the biological membranes. In contrast, fungal cPLA2-like proteins are much less characterized and their roles have remained elusive. AoPlaA is a cPLA2-like protein in the filamentous fungus Aspergillus oryzae which, unlike mammalian cPLA2, localizes to mitochondria. In this study, we investigated the biochemical and physiological functions of AoPlaA. Recombinant AoPlaA produced in E. coli displayed Ca2+-independent lipolytic activity. Mass spectrometry analysis demonstrated that AoPlaA displayed PLA2 activity to phosphatidylethanolamine (PE), but not to other phospholipids, and generated 1-acylated lysoPE. Catalytic site mutants of AoPlaA displayed almost no or largely reduced activity to PE. Consistent with PE-specific activity of AoPlaA, AoplaA-overexpressing strain showed decreased PE content in the mitochondrial fraction. In contrast, AoplaA-disruption strain displayed increased content of cardiolipin. AoplaA-overexpressing strain, but not its counterparts overexpressing the catalytic site mutants, exhibited retarded growth at low temperature, possibly because of the impairment of the mitochondrial function caused by excess degradation of PE. These results suggest that AoPlaA is a novel PE-specific PLA2 that plays a regulatory role in the maintenance of mitochondrial phospholipid composition.
