The central domain is required to target and anchor perilipin A to lipid droplets

Abstract

The perilipins are the most abundant proteins coating the surfaces of lipid droplets in adipocytes and are found at lower levels surrounding lipid droplets in steroidogenic cells. Perilipins drive triacylglycerol storage in adipocytes by regulating the rate of basal lipolysis and are also required to maximize hormonally stimulated lipolysis. To map the domains that target and anchor perilipin A to lipid droplets, we stably expressed fragments of perilipin A in 3T3-L1 fibroblasts. Immunofluorescence microscopy and immunoblotting of proteins from isolated lipid droplets revealed that neither the amino nor the carboxyl terminus is required to target perilipin A to lipid droplets; however, there are multiple, partially redundant targeting signals within a central domain including 25% of the primary amino acid sequence. A peptide composed of the central domain of perilipin A directed a fused green fluorescent protein to the surfaces of lipid droplets. Full-length perilipin A associates with lipid droplets via hydrophobic interactions, as shown by the persistence of perilipins on lipid droplets after centrifugation through an alkaline carbonate solution. Results of the mutagenesis studies indicate that the sequences responsible for anchoring perilipin A to lipid droplets are most likely domains of moderately hydrophobic amino acids located within the central 25% of the protein. Thus, we conclude that the central 25% of the perilipin A sequence contains all of the amino acids necessary to target and anchor the protein to lipid droplets.