Primary structure, functional characteristics and tissue expression pattern of human ATA2, a subtype of aminoacid transport system A

We report here on the primary structure and functional characteristics of t he protein responsible for the system A amino acid transport activity that is known to be expressed in most human tissues. This transporter, designate d ATA? for amino acid transporter A2, was cloned from the human hepatoma ce ll line HepG2. Human ATA2 (hATA2) consists of 506 amino acids and exhibits a high degree of homology to rat ATA2. hATA2-specific mRNA is ubiquitously expressed in human tissues. When expressed in mammalian cells, hATA2 mediat es Na+-dependent transport of alpha-(methylamino)isobutyric acid, a specifi c model substrate for system A. The transporter is specific for neutral ami no acids. It is pH-sensitive and Li+-intolerant. The Na+-amino acid stoichi ometry is 1:1. (C) 2000 Elsevier Science B.V. All rights reserved.