Mitochondrial β-oxidation in Aspergillus nidulans

Abstract

β-Oxidation (β-ox) occurs exclusively in the peroxisomes of Saccharomyces cerevisiae and other yeasts, leading to the supposition that fungi lack mitochondrial β-ox. Here we present unequivocal evidence that the filamentous fungus Aspergillus nidulans houses both peroxisomal and mitochondrial β-ox. While growth of a peroxisomal β-ox disruption mutant (ΔfoxA) was eliminated on a very long-chain fatty acid (C 22:1), growth was only partially impeded on a long-chain fatty acid (C18:1) and was not affected at all on short chain (C 4-C6) fatty acids. In contrast, growth of a putative enoyl-CoA hydratase mutant (ΔechA) was abolished on short-chain and severely restricted on long- and very long-chain fatty acids. Furthermore fatty acids inhibited growth of the ΔechA mutant but not the ΔfoxA mutant in the presence of an alternate carbon source (lactose). Disruption of echA led to a 28-fold reduction in 2-butenoyl-CoA hydratase activity in a preparation of organelles. EchA was also required for growth on isoleucine and valine. The subcellular localization of the FoxA and EchA proteins was confirmed through the use of red and green fluorescent protein fusions.