DDHD2 possesses both lipase and transacylase capacities that remodel triglyceride acyl chains

Hereditary spastic paraplegia subtype SPG54 is a genetic neurological disorder caused by mutations in the DDHD2 gene. Excessive lipid droplet accumulation is observed in the brains of SPG54 patients and DDHD2 knockout mice, consistent with DDHD2s reported neutral lipase activity. Here, we find recombinant human DDHD2 preferentially hydrolyzes diacylglycerol (DAG) over phospholipids, with a slight preference for DAG over triacylglycerol (TAG). DDHD2 also exhibits transacylase activity, which enables transfer of acyl chains from triacylglycerols to diacylglycerols and monoacylglycerols to remodel the acyl chains of triglycerides. A predicted hydrophobic amphipathic helix on DDHD2 is essential for lipid droplet binding in vitro and in cells, and its lack reduces the enzymatic activity and triglyceride acyl chain remodeling. Adipose triglyceride lipase (ATGL), but not hormone sensitive lipase (HSL), also has transacylation activity and can remodel triglyceride acyl chains, but to a lesser extent than DDHD2. Taken together, this provides evidence that DDHD2 is a neutral lipid lipase and transacylase whose broad specificity enables triglyceride acyl-chain remodeling. SIGNIFICANCE STATEMENTTriglycerides (TAGs), the primary form of long-term energy storage, have acyl chain compositions crucial for diverse cellular processes. Lipases typically hydrolyze TAGs into free fatty acids. Here, we reveal a novel function for the neutral lipid lipase DDHD2: a transacylase activity. Instead of releasing fatty acids, DDHD2 transfers them between neutral lipids, altering TAG acyl chain composition. This transacylation requires the unique oil environment of lipid droplets (LDs), which excludes water from DDHD2s lipolytic active site, favoring transacylation over hydrolysis. DDHD2s lipase and transacylase activities enable TAG acyl-chain remodeling, demonstrating the possibility that a single enzyme can catalyze TAG cycling. This finding has implications for understanding lipid metabolism, LD dynamics, and specific motor neuron diseases implicating DDHD2.