Abstract
The neutral amino acid transporter alanine-serine-cysteine transporter 2 (ASCT2) belongs to the solute carrier 1 (SLC1) family of solute transporters and transports small, neutral amino acids across the membrane, including the physiologically important and ubiquitous amino acid glutamine. Our understanding of the involvement of ASCT2 in the physiological processes involving glutamine is hampered by a lack of understanding of its pharmacology and the absence of high-affinity inhibitors. In this study, we combined an in silico docking approach with experimental investigation of binding parameters to develop new ASCT2 inhibitors and substrates, a series of serine esters, and to determine structural parameters that govern their functional effects. The series of compounds was synthesized using standard methods and exhibited a range of properties, from inhibitors to partial substrates and full substrates. Our results suggest that amino acid derivatives with small side-chain volume and low side-chain hydrophobicity interact strongly with the closed-loop form of the binding site, in which re-entrant loop 2, the presumed extracellular gate for the substrate binding site, is closed off. However, these derivatives bind weakly to the open-loop form (external gate open to the extracellular side), acting as transported substrates. In contrast, inhibitors bind preferentially to the open-loop form. An aromatic residue in the side chain is required for high-affinity interaction. One of the compounds, the l-serine ester serine biphenyl-4-carboxylate reversibly inhibits ASCT2 function with an apparent affinity of 30 μM.
Footnotes
This work was supported by the National Institutes of Health National Institute of Neurological Disorders and Stroke [Grant 2R01-NS049335-06A1] (to C.G.); and the Binational Science Foundation [Grant 2007051] (to C.G.).
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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ABBREVIATIONS:
- ASCT
- alanine-serine-cysteine transporter
- EAAT
- excitatory amino acid transporter
- HEK
- human embryonic kidney
- DMSO
- dimethyl sulfoxide
- NaMes
- sodium methanesulfonate
- GltPh
- glutamate transporter homolog from Pyrococcus horikoshii
- PDB
- Protein Data Bank
- RL
- re-entrant loop
- TBOA
- dl-threo-β-benzyloxyaspartic acid
- LAT
- system l-amino acid transporter.
- Received September 8, 2011.
- Accepted November 23, 2011.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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