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). As part of the SPAP complex, activates spermatozoa motility (By similarity). Homodimer (By similarity). Interacts with APOA1BP and CLU. Component of a sperm activating protein complex (SPAP), consisting of APOA1, an immunoglobulin heavy chain, an immunoglobulin light chain and albumin. Interacts with NDRG1. Interacts with SCGB3A2 (By similarity). Interacts with NAXE and YJEFN3 (By similarity). Glycosylated. Palmitoylated. Phosphorylation sites are present in the extracellular medium. Belongs to the apolipoprotein A1/A4/E family.