Voltage-dependent processes in the electroneutral amino acid exchanger ASCT2
Catherine B Zander1, Thomas Albers, Christof Grewer
1Department of Chemistry, Binghamton University, Binghamton, NY 13902, USA.
The Journal of General Physiology
|May 15, 2013
Summary
The alanine serine cysteine transporter 2 (ASCT2) facilitates amino acid exchange, coupled with sodium ions. This transport is voltage-dependent, occurring on a millisecond timescale, with a stoichiometry of at least 2:1 sodium to amino acid.
Area of Science:
- Biochemistry
- Molecular Biology
- Membrane Transport
Background:
- The alanine serine cysteine transporter 2 (ASCT2) mediates neutral amino acid exchange.
- Previous studies suggested ASCT2 transport is electroneutral, coupled to one Na(+) ion.
- Limited information exists on the electrical properties of ASCT2-mediated amino acid transport.
Purpose of the Study:
- To elucidate the detailed mechanism of amino acid exchange by ASCT2.
- To investigate the electrical properties and voltage dependence of ASCT2 transport.
- To determine the stoichiometry of Na(+) and amino acid cotransport.
Main Methods:
- Experimental approaches including electrophysiology and substrate concentration jumps.
- Computational methods utilizing molecular dynamics simulations.
- Analysis of Na(+) dependence of ASCT2-associated currents.
Main Results:
- ASCT2 Na(+)/amino acid stoichiometry is at least 2:1, with Na(+) binding to the apo form.
- The transport domain carries a net positive charge (+0.81) when loaded with substrate and two Na(+) ions.
- Voltage steps induced millisecond-timescale transient currents, and alanine concentration jumps caused inward currents, indicating net positive charge translocation.
Conclusions:
- ASCT2-mediated amino acid exchange is voltage-dependent and operates on a millisecond timescale.
- A sequential binding model involving Na(+) ions and amino acid substrate is proposed.
- ASCT2 transport mechanisms and Na(+) interactions are conserved within the solute carrier 1 family.
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