Yarrowia Lipolytica AAL Genes Are Involved in Peroxisomal Fatty Acid Activation

In yeast, β-oxidation of fatty acids (FAs) essentially takes place in peroxisomes, and FA activation must precede FA oxidation. In Saccharomyces cerevisiae, a single fatty-acyl–CoA-synthetase, ScFaa2p, mediates peroxisomal FA activation. We have previously shown that this reaction also exists in the oleaginous yeast Yarrowia lipolytica; however, the protein involved in this process remains unknown. Here, we found that proteins, named Aal proteins (Acyl/Aryl-CoA-ligases), resembling the 4-coumarate–CoA-ligase-like enzymes found in plants are involved in peroxisomal FA activation in Y. lipolytica; Y. lipolytica has 10 AAL genes, eight of which are upregulated by oleate. All the Aal proteins contain a PTS1-type peroxisomal targeting sequence (A/SKL), suggesting a peroxisomal localization. The function of the Aal proteins was analyzed using the faa1Δant1Δ mutant strain, which demonstrates neither cytoplasmic FA activation (direct result of FAA1 deletion) nor peroxisomal FA activation (indirect result of ANT1 deletion, a gene coding an ATP transporter). This strain is thus highly sensitive to external FA levels and unable to store external FAs in lipid bodies (LBs). Whereas the overexpression of (cytoplasmic) AAL1ΔPTS1 was able to partially complement the growth defect observed in the faa1Δant1Δ mutant on short-, medium- and long-chain FA media, the presence of Aal2p to Aal10p only allowed growth on the short-chain FA medium. Additionally, partial LB formation was observed in the oleate medium for strains overexpressing Aal1ΔPTS1p, Aal4ΔPTS1p, Aal7ΔPTS1p, and Aal8ΔPTS1p. Finally, an analysis of the FA content of cells grown in the oleate medium suggested that Aal4p and Aal6p present substrate specificity for C16:1 and/or C18:0.