Human LAT1, a Subunit of System L Amino Acid Transporter: Molecular Cloning and Transport Function

We report here on the cloning and functional characterization of human LAT1, a subunit of the amino acid transport system L. The hLAT1 cDNA, obtained from a human placental cDNA library, codes for a protein of 507 amino acids. When functionally expressed in mammalian cells together with the heavy chain of the rat 4F2 antigen (r4F2hc), hLAT1 induces the transport of neutral amino acids. When expressed independently, neither hLAT1 nor r4F2hc was capable of amino acid transport to any significant extent. Thus, the hLAT1-r4F2hc heterodimeric complex is responsible for the observed amino acid transport. The transport process induced by the heterodimer is Na+ independent and is not influenced by pH. It recognizes exclusively neutral amino acids with high affinity. LAT1-specific mRNA is expressed in most human tissues with the notable exception of the intestine.