The involvement of sodium in the function of the human amino acid transporter ASCT2

Alanine, serine, cysteine transporter 2 (ASCT2) is a membrane amino acid transporter with relevance to human physiology and pathology, such as cancer. Notwithstanding, the study on the ASCT2 transport cycle still has unknown aspects, such as the role of Na+ in this process. We investigate this issue using recombinant hASCT2 reconstituted in proteoliposomes. Changes in the composition of purification buffers show the crucial role of Na+ in ASCT2 functionality. The transport activity is abolished when Na+ is absent or substituted by Li+ or K+ in purification buffers. By employing a Na+ fluorometric probe, we measured an inwardly directed flux of Na+ and, by combining fluorometric and radiometric assays, determined a 2Na(+) : 1Gln stoichiometry. Kinetics of Na+ transport suggest that pH-sensitive residues are involved in Na+ binding/transport. Our results clarify the role of Na+ on human ASCT2 transporter activity.

Automated summary

The study showed the crucial role of Na+ in the functionality of human ASCT2 transporter, as transport activity is abolished when Na+ is absent or substituted by Li+ or K+ in purification buffers. Experimentally determined 2Na+ : 1Gln stoichiometry, and kinetics suggest the involvement of pH-sensitive residues in Na+ binding/transport process.