Do Amino Acid Antiporters Have Asymmetric Substrate Specificity?

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Amino acid antiporters facilitate 1:1 exchange of amino acids.
• Systematic investigation of asymmetric transport in different transporter conformations is lacking.

Purpose of the Study:

• To investigate substrate specificity differences in inward and outward facing conformations of amino acid antiporters.
• To identify non-canonical transport modes.

Main Methods:

• Utilized liquid chromatography-mass spectrometry (LC-MS).
• Employed ¹²C- and ¹³C-labeled amino acid mixtures.
• Analyzed transport across *Xenopus laevis* oocyte plasma membranes expressing various antiporters.

Main Results:

• Observed distinct substrate specificities among transporter paralogs.
• Demonstrated largely symmetric transport for most antiporters, equalizing amino acid pools.
• Identified asymmetric transport in y⁺LAT1 and y⁺LAT2 (Na⁺-dependent neutral amino acid import).
• Found glycine as a selective influx substrate for ASCT1 and ASCT2.
• Identified proline as a selective influx substrate for ASCT1.

Conclusions:

• Amino acid antiporters are generally symmetric but can exhibit non-canonical transport.
• Specific antiporters like y⁺LAT1/2, ASCT1, and ASCT2 display unique substrate specificities and transport mechanisms.