BPS2026 – The membrane biophysics of ABHD5-regulated lipolysis

ABHD5 is an ancient pseudoenzyme that has evolved to be a critical regulator of lipolysis. It senses the cell’s metabolic needs and regulates the storage and mobilization of lipids by activating or deactivating lipid hydrolases, including members of the Patatin-like phospholipase domain-containing protein (PNPLA) family. We hypothesize that lipid packing defects guide ABHD5 sorting between monolayers and bilayers. Lipid packing defects are voids on the surface of lipid droplets where the hydrophobic inner core, which consists of the phospholipid tails, is exposed to the aqueous environment. To investigate this mechanism, we are integrating experimental and computational approaches to uncover the molecular details of how ABHD5 sorts between intracellular membranes and selectively activates enzymes based on its conformation. Our results show that ABHD5 preferentially binds to LD monolayers enriched with triacylglycerol (TAG), but we also observed a variation in ABHD5 association with bilayers in the presence of different neutral lipid types. To further validate these results, we performed coarse-grain molecular dynamics simulations (CG-MD) to study the correlation between packing defects and different neutral lipids. Additionally, fluorescence lifetime measurements (FLIM) results show a change in lifetime of the fluorophore NR12S among these neutral lipids suggesting a change in membrane packing. Our future work will involve both experimental and simulation works to understand how ABHD5 senses these packing defects. In sum, these studies contribute to advancing our understanding of membrane dynamics and identifying potential therapeutic targets for lipid-related metabolic disorders.