The apelin receptor (APJ), originally designated as an orphan G protein-coupled receptor (GPCR), has the typical 7-transmembrane structure of class A GPCRs, and is comprised of 380 amino acid residues. The receptor has also been found in various other species, such as mouse, rat, cow, and rhesus monkey. APJ plays a role in the regulation of cardiovascular, immunomodulatory, and gastrointestinal function, in addition to fluid homeostasis. APJ has also been discovered to be an HIV co-receptor which, when blocked by apelin peptides, effectively inhibits infection.
