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 (PubMed:8702519, PubMed:29872227). 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 (PubMed:10708449, PubMed:23492904). (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. Homotrimer (Probable) (PubMed:29872227). Interacts with ERVH48-1/suppressyn; may negatively regulate syncytialization (PubMed:23492904). Identified by mass spectrometry in melanosome fractions from stage I to stage IV. A number of isoforms are produced by alternative initiation. Isoforms start at multiple alternative CUG and GUG codons. Placenta, lung, skeletal muscle, kidney, pancreas, and intestine. Belongs to the dicarboxylate/amino acid:cation symporter (DAACS) (TC 2.A.23) family. SLC1A5 subfamily.