Plays a crucial role in the formation of lipid droplets (LDs) which are storage organelles at the center of lipid and energy homeostasis (By similarity). In association with LDAF1, defines the sites of LD formation in the ER (By similarity). Also required for growth and maturation of small nascent LDs into larger mature LDs (By similarity). Mediates the formation and/or stabilization of endoplasmic reticulum-lipid droplets (ER-LD) contacts, facilitating protein and lipid delivery from the ER into growing LDs (By similarity). Regulates the maturation of ZFYVE1-positive nascent LDs and the function of the RAB18-ZFYVE1 complex in mediating the formation of ER-LD contacts (By similarity). Binds anionic phospholipids including phosphatidic acid (By similarity). Plays an important role in the differentiation and development of adipocytes (By similarity). Undecamer (an oligomer having eleven subunits) (By similarity). Oligomerization is important for its function in lipid droplet formation (By similarity). Interacts with LDAF1 to form an oligomeric complex (By similarity). Interacts with RAB18 (By similarity). Interacts with ZFYVE1 in a RAB18-dependent manner (By similarity). Localizes at endoplasmic reticulum-lipid droplets (ER-LD) contact sites. Belongs to the seipin family.