Lipid droplet targeting domains of adipophilin

Adipophilin (ADPH), a prominent protein component of lipid storage droplets (LSDs), is postulated to be necessary for the formation and cellular function of these structures. The presence of significant sequence similarities within an approximately 100 amino acid region of the N-terminal portions of ADPH and related LSD binding proteins, perilipin and TIP47, has implicated this region, known as the "PAT" domain, in LSD targeting. Here we investigate the role of the PAT domain in targeting ADPH to LSDs by expressing this region, as well as selected N- and C-terminal truncations of mouse ADPH in COS7 cells as epitope-tagged fusion proteins. Our studies show that truncations lacking either the PAT domain or the C-terminal half of ADPH both correctly targeted LSDs and increased the LSD content of transfected cells. Neither the PAT domain nor the C-terminal half of ADPH appeared to target LSDs or affect the LSD number. Instead, targeting fragments encompassed a putative alpha-helical region between amino acids 189 and 205, implicating this region in both LSD targeting and regulation of LSD formation.