Fatty acid compartmentalization

Before long‐chain fatty acids can be oxidized or used to synthesize complex lipids, they must be activated by one of the acyl‐CoA synthetase (ACSL) family members. Our data in liver, heart, and skeletal muscle has suggested that each activating ACSL isoform can direct fatty acids towards or away from specific downstream pathways. Because we hypothesized that directionality must occur via specific protein interactions, we used the protein interaction discovery technique, BioID, to determine interacting protein partners and function. We targeted ACSL isoform‐1 either to the ER or to the outer mitochondrial membrane (OMM) of Hepa1–6 cells as a fusion protein with the modified E.coli biotin ligase, BirA*. In the presence of added biotin, BirA irreversibly biotinylates proteins that are in close proximity to the ACSL1 bait. Mass spectrometry identified 98 proteins that interacted only with the ER‐targeted ACSL1, 55 proteins that interacted only with the OMM‐targeted ACSL1, and 43 proteins that interacted with both targeted ACSL1 constructs. We selected a subset of lipid droplet and vesicle proteins for confirmation by co‐immunoprecipitation and functional studies. At the OMM, ACSL1 interacted with lipid droplet tethering proteins in a glucose‐dependent manner. At the ER, ACSL1 interacted with proteins involved in ceramide synthesis and with ER and peroxisomal proteins involved in peroxisomal oxidation of niche fatty acids. Thus, we have captured a novel snapshot of key proteins that may influence ACSL1 function and determine downstream partitioning of acyl‐CoAs. Support or Funding Information DK56598, DK59935 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .