Participates in the reverse transport of cholesterol from tissues to the liver for excretion by promoting cholesterol efflux from tissues and by acting as a cofactor for the lecithin cholesterol acyltransferase (LCAT). Homodimer (By similarity). Interacts with NAXE and YJEFN3 (PubMed:23719382). Highly expressed in the yolk syncytial layer during embryonic (starting at the gastrula stage) and early larval development, an extraembryonic structure implicated in embryonic and larval nutrition. Belongs to the apolipoprotein A1/A4/E family.