Lipid composition-driven sorting of ABHD5 between monolayer and bilayer surfaces

Lipid droplets, or LDs, are essential organelles responsible for storing neutral lipids and controlling lipid homeostasis. Their structure consists of a hydrophobic core of triacylglycerols and sterol esters, surrounded by a phospholipid monolayer. This unique organization results in biophysical properties that direct specific protein recruitment.

Among the proteins associated with LDs, β-hydrolase domain-containing protein 5 (ABHD5), also known as CGI-58, plays a crucial role in lipolysis and overall lipid metabolism. However, the mechanisms regulating ABHD5's distribution between endoplasmic reticulum (ER) bilayers and LD monolayers are not well understood. Proper membrane association of ABHD5 is vital for activating PNPLA family lipases, making it crucial to decipher the factors influencing its membrane selectivity for a comprehensive understanding of LD function in health and disease.

In this study, researchers investigated ABHD5's binding and sorting behavior using model membrane systems consisting of giant unilamellar vesicles (GUVs) and droplet-embedded vesicles (DEVs). These systems incorporated defined phospholipid and neutral lipid compositions. By combining experimental assays with computational modeling, the researchers quantified how ABHD5 partitions between bilayer membranes resembling the ER and monolayer surfaces resembling LDs.

By systematically varying membrane composition and physical properties, they assessed how packing defects and neutral lipid content shape ABHD5 localization. Their findings reveal the biophysical features that favor ABHD5 association with LD-like monolayers, providing new mechanistic insights into how cells target regulatory proteins to distinct membrane environments to regulate lipid metabolism.