Bröer S, Palacín M. The role of amino acid transporters in inherited and acquired diseases

Research School of Biology, Australian National University, Canberra, ACT 0200, Australia.
Biochemical Journal (Impact Factor: 4.4). 06/2011; 436(2):193-211. DOI: 10.1042/BJ20101912
Source: PubMed


Amino acids are essential building blocks of all mammalian cells. In addition to their role in protein synthesis, amino acids play an important role as energy fuels, precursors for a variety of metabolites and as signalling molecules. Disorders associated with the malfunction of amino acid transporters reflect the variety of roles that they fulfil in human physiology. Mutations of brain amino acid transporters affect neuronal excitability. Mutations of renal and intestinal amino acid transporters affect whole-body homoeostasis, resulting in malabsorption and renal problems. Amino acid transporters that are integral parts of metabolic pathways reduce the function of these pathways. Finally, amino acid uptake is essential for cell growth, thereby explaining their role in tumour progression. The present review summarizes the involvement of amino acid transporters in these roles as illustrated by diseases resulting from transporter malfunction.

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Available from: Stefan Bröer, Sep 29, 2015
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    • "Amino acid flux through biological membranes and distribution to tissues are both finely controlled by numerous transporters belonging to different solute carrier (SLC) families. Many of these amino acid transporters are characterized functionally [1] [2] [3] [4] [5] but much is still unknown concerning their structure/function relationships, protein– protein interactions and trafficking. Among these transporters, SLC1A5, known as ASCT2, is one of the most attractive to study due to its involvement in cell signaling and relevance to human pathology. "
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    ABSTRACT: The human amino acid transporter SLC1A5 (ASCT2) contains two N-glycosylation sites (N163 and N212) located in the large extracellular loop. In the homology structural model of ASCT2 these Asn residues are extracellularly exposed. Mutants of the two Asn exhibited altered electrophoretic mobility. N163Q and N212Q displayed multiple bands with apparent molecular masses from 80 kDa to 50 kDa. N163/212Q displayed a single band of 50 kDa corresponding to the unglycosylated protein. The presence in membrane of WT and mutants was evaluated by protein biotinylation assay followed by immunoblotting. The double mutation significantly impaired the presence of the protein in membrane, without impairment in protein synthesis. [(3)H]glutamine transport was measured in cells transiently transfected with the WT or mutants. N163/212Q exhibited a strongly reduced transport activity correlating with reduced surface expression. The same proteins extracted from cells and reconstituted in liposomes showed comparable transport activities demonstrating that the intrinsic transport function of the mutants was not affected. The rate of endocytosis of ASCT2 was assayed by a reversible biotinylation strategy. N212Q and N163/212Q showed strongly increased rates of endocytosis respect to WT. ASCT2 stability was determined using cycloheximide. N163Q or N163/212Q showed a slightly or significantly lower stability with respect to WT. To assess trafficking to the membrane, a brefeldin-based assay, which caused retention of proteins in ER, was performed. One hour after brefeldin removal WT protein was localized to the plasma membrane while the double mutant was localized in the cytosol. The results demonstrate that N-glycosylation is critical for trafficking. Copyright © 2015. Published by Elsevier B.V.
    Full-text · Article · Apr 2015 · Biochimica et Biophysica Acta
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    • "Among the most interesting transporters in human physiology and pathology there is the Na + -dependent glutamine/neutral amino acid transporter ASCT2 (SLC1A5) previously known in humans as ATB0. This transport system has been identified in human cell systems even though the kinetic properties and substrate specificity are not fully understood [2] [3] [12] while the rodent isoform, besides being studied in cell systems [13] [14] [15] [16], has been also functionally and kinetically characterized in proteoliposomes [9] [17] [18]. Basic functional and kinetic parameters of the kidney rat protein determined in both experimental models correlated well. "
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    ABSTRACT: The human glutamine/neutral amino acid transporter ASCT2 (hASCT2) was over-expressed in P. pastoris and purified by Ni(2+)-chelating and gel filtration chromatography. The purified protein was reconstituted in liposomes by detergent removal with a batch-wise procedure. Time dependent [(3)H]glutamine/glutamine antiport was measured in proteoliposomes which was active only in the presence of external Na(+). Internal Na(+) slightly stimulated the antiport. Optimal activity was found at pH 7.0. A substantial inhibition of the transport was observed by Cys, Thr, Ser, Ala, Asn and Met (≥ 70%) and by mercurials and methanethiosulfonates (≥ 80%). Heterologous antiport of [(3)H]glutamine with other neutral amino acids was also studied. The transporter showed asymmetric specificity for amino acids: Ala, Cys, Val, Met were only inwardly transported, while Gln, Ser, Asn, and Thr were transported bi-directionally. From kinetic analysis of [(3)H]glutamine/glutamine antiport Km values of 0.097 and 1.8 mM were measured on the external and internal sides of proteoliposomes, respectively. The Km for Na(+) on the external side was 32 mM. The homology structural model of the hASCT2 protein was built using as template the GltPh of P. horikoshii. Cys395 was the only Cys residue externally exposed, thus being the potential target of SH reagents inhibition and, hence, potentially involved in the transport mechanism.
    Full-text · Article · Jun 2013 · Biochimica et Biophysica Acta
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    • "In the cells of different organs, AAs may then serve as building blocks for the synthesis of structural and functional proteins, may be used for cellular metabolism or function as signalling molecules (Verrey et al. 2009; Wu, 2009). Therefore, AA transfer across plasma membranes via various cooperating AA transporters plays a crucial role for body AA homeostasis , and the defect of transporters leads to several diseases (Verrey et al. 2009; Broer & Palacin, 2011). The best characterized basolateral AA transporters of the small intestine and proximal kidney tubule (re)absorbing epithelia are the abundant Lat2–4F2hc (Slc7a8) and y + Lat1–4F2hc (Slc7a7) that function as obligatory exchangers (antiporters). "
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    ABSTRACT: The uniporter TAT1 (Slc16a10) mediates the facilitated diffusion of aromatic amino acids across basolateral membranes of kidney, small intestine and liver epithelial cells and across the plasma membrane of non-epithelial cells like skeletal myocytes. Its role for body amino acid homeostasis was now investigated using newly generated TAT1 (Slc16a10) defective mice (tat1-/-). These mice grow and reproduce normally, show no gross phenotype and no obvious neurological defect. Histological analysis did not reveal abnormalities and there is no compensatory change in any tested amino acid transporter mRNA. TAT1 null mice display however increased plasma, muscle and kidney aromatic amino acid concentration under both normal and high protein diet, although this concentration remains normal in liver. A major aromatic aminoaciduria and a smaller urinary loss of all substrates additionally transported by L-type amino acid antiporter Lat2-4F2hc (Slc7a8) were revealed under high protein diet. This suggests an epithelial transport defect as also shown by the accumulation of intravenously injected 123I-2-I-L-Phe in kidney and of 3H-L-Phe in ex vivo everted gut sac enterocytes. Taken together, these data indicate that the uniporter TAT1 is required to equilibrate the concentration of aromatic amino acids across specific membranes. For instance, it enables hepatocytes to function as sink that controls the extracellular aromatic amino acid concentration. Additionally, it facilitates the release of aromatic amino acids across the basolateral membrane of small intestine and proximal kidney tubule epithelial cells, thereby allowing the efflux of other neutral amino acids presumably via Lat2-4F2hc.
    Full-text · Article · Oct 2012 · The Journal of Physiology
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