Sodium-dependent amino acids transporter that has a broad substrate specificity, with a preference for zwitterionic amino acids. It accepts as substrates all neutral amino acids, including glutamine, asparagine, and branched-chain and aromatic amino acids, and excludes methylated, anionic, and cationic amino acids. Through binding of the fusogenic protein syncytin-1/ERVW-1 may mediate trophoblasts syncytialization, the spontaneous fusion of their plasma membranes, an essential process in placental development.; (Microbial infection) Acts as a cell surface receptor for Feline endogenous virus RD114.; (Microbial infection) Acts as a cell surface receptor for Baboon M7 endogenous virus.; (Microbial infection) Acts as a cell surface receptor for type D simian retroviruses.