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Carolin Willner, Jennifer Sapia, Bianca M. Esch, Pia Erdbrügger, Sergej Limar, Sebastian Eising, Carolin Körner, Stefano Vanni, Florian Fröhlich (Osnabrück University; Department of Biology/Chemistry; Bioanalytical Chemistry section; 49076 Osnabrück, Germany; )
Fatty acids have to be activated with a molecule of Coenzyme A (CoA) to be utilized as the building blocks for membrane lipids. A special class of fatty acids are the very long chain fatty acids (VLCFAs) harboring 22 to 26 carbon atoms. The sole VLCFA-CoA synthetase in S. cerevisiae is the protein Fat1. However, the localization of free VLCFAs and that of Fat1 remain unclear. With the combination of molecular dynamic simulations and biochemical methods, we show that free VLCFAs partition into the neutral core of lipid droplets (LDs). We identify that Fat1 is targeted to LDs via an N-terminal amphipathic helix but can also localize to the endoplasmic reticulum in the absence of LDs. Structural predictions of Fat1 suggest a hydrophobic cavity that spans the protein from its active site to the membrane-targeting amphipathic helix. Together our results suggest that VLCFAs can reach the Fat1 active site directly from the core of LDs. Our model offers a molecular explanation for how the very hydrophobic VLCFAs can reach a cytosolic active site of a protein. Our data support a model in which organelle targeting motifs co-evolved with the biophysical properties of metabolites.