Epithelial neutral amino acid transporters

Glutathione (GSH) is an endogenous tripeptide antioxidant that consists of glutamate-cysteine-glycine. GSH content is limited by the availability of glutamate and cysteine. Furthermore, glutamine is involved in the regulation of GSH synthesis via the glutamate–glutamine cycle. P2X7 receptor (P2X7R) is one of the cation-permeable ATP ligand-gated ion channels, which is involved in neuronal excitability, neuroinflammation and astroglial functions. In addition, P2X7R activation decreases glutamate uptake and glutamine synthase (GS) expression/activity. In the present study, we found that P2X7R deletion decreased the basal GSH level without altering GSH synthetic enzyme expressions in the mouse hippocampus. P2X7R deletion also increased expressions of GS and ASCT2 (a glutamine:cysteine exchanger), but diminished the efficacy of N-acetylcysteine (NAC, a GSH precursor) in the GSH level. SIN-1 (500 μM, a generator nitric oxide, superoxide and peroxynitrite), which facilitates the cystine–cysteine shuttle mediated by xCT (a glutamate/cystein:cystine/NAC antiporter), did not affect basal GSH concentration in WT and P2X7R knockout (KO) mice. However, SIN-1 effectively reduced the efficacy of NAC in GSH synthesis in WT mice, but not in P2X7R KO mice. Therefore, our findings indicate that P2X7R may be involved in the maintenance of basal GSH levels by regulating the glutamate–glutamine cycle and neutral amino acid transports under physiological conditions, which may be the defense mechanism against oxidative stress during P2X7R activation.

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Glycine enhances microglial intracellular calcium signaling. A role for sodium-coupled neutral amino acid transporters

Pflügers Archiv - European Journal of Physiology ◽

10.1007/s00424-011-0939-0 ◽

2011 ◽

Vol 461 (4) ◽

pp. 481-491 ◽

Cited By ~ 4

Author(s):

Jimmy Van den Eynden ◽

Kristof Notelaers ◽

Bert Brône ◽

Daniel Janssen ◽

Katherine Nelissen ◽

...

Keyword(s):

Amino Acid ◽

Calcium Signaling ◽

Intracellular Calcium ◽

Neutral Amino Acid ◽

Amino Acid Transporters ◽

Intracellular Calcium Signaling

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Discovery and synthesis of hydroxy-L-proline based blockers of the neutral amino acid transporters SLC1A4 (ASCT1) and SLC1A5 (ASCT2).

10.1101/2021.12.14.470456 ◽

2021 ◽

Author(s):

Michael P Kavanaugh ◽

Brent R. Lyda ◽

Gregory P. Leary ◽

Derek Silvius ◽

Nicholas R. Natale ◽

...

Keyword(s):

Amino Acid ◽

Homology Model ◽

Neutral Amino Acid ◽

Amino Acid Transporters ◽

Biological Targets ◽

Conformationally Restricted ◽

New Class ◽

Wide Range ◽

Ligand Binding Sites ◽

Proline Derivatives

The conformationally restricted heterocycle hydroxy-ʟ-proline is a versatile scaffold for the synthesis of diverse multi-functionalized pyrrolidines for probing the ligand binding sites of biological targets. With the goal to develop new inhibitors of the widely expressed amino acid transporters SLC1A4 and SLC1A5 (also known as ASCT1 and ASCT2), we synthesized and functionally screened a series of hydroxy-ʟ-proline derivatives or 'prolinols' using electrophysiological and radio-labeled uptake assays on amino acid transporters from the SLC1, SLC7, and SLC38 solute carrier families. We identified a number of synthetic prolinols that act as selective high-affinity inhibitors of the SLC1 functional subfamily comprising the neutral amino acid transporters SLC1A4 and SLC1A5. The active and inactive prolinols were computationally docked into a threaded homology model and analyzed with respect to predicted molecular orientation and observed pharmacological activity. The series of hydroxy-L-proline derivatives identified here represents a new class of potential agents to pharmacologically modulate SLC1A4 and SLC1A5, amino acid exchangers that play important roles in a wide range of physiological and pathophysiological processes.

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Structural Features of the Glutamate Transporter Family

Microbiology and Molecular Biology Reviews ◽

10.1128/mmbr.63.2.293-307.1999 ◽

1999 ◽

Vol 63 (2) ◽

pp. 293-307 ◽

Cited By ~ 98

Author(s):

Dirk Jan Slotboom ◽

Wil N. Konings ◽

Juke S. Lolkema

Keyword(s):

Amino Acid ◽

Glutamate Transporter ◽

Glutamate Transporters ◽

Amino Acid Sequences ◽

Neutral Amino Acid ◽

Amino Acid Transporters ◽

Conserved Sequence ◽

Transporter Family ◽

The Family ◽

Membrane Spanning

SUMMARY Neuronal and glial glutamate transporters remove the excitatory neurotransmitter glutamate from the synaptic cleft and thus prevent neurotoxicity. The proteins belong to a large and widespread family of secondary transporters, including bacterial glutamate, serine, and C4-dicarboxylate transporters; mammalian neutral-amino-acid transporters; and an increasing number of bacterial, archaeal, and eukaryotic proteins that have not yet been functionally characterized. Sixty members of the glutamate transporter family were found in the databases on the basis of sequence homology. The amino acid sequences of the carriers have diverged enormously. Homology between the members of the family is most apparent in a stretch of approximately 150 residues in the C-terminal part of the proteins. This region contains four reasonably well-conserved sequence motifs, all of which have been suggested to be part of the translocation pore or substrate binding site. Phylogenetic analysis of the C-terminal stretch revealed the presence of five subfamilies with characterized members: (i) the eukaryotic glutamate transporters, (ii) the bacterial glutamate transporters, (iii) the eukaryotic neutral-amino-acid transporters, (iv) the bacterial C4-dicarboxylate transporters, and (v) the bacterial serine transporters. A number of other subfamilies that do not contain characterized members have been defined. In contrast to their amino acid sequences, the hydropathy profiles of the members of the family are extremely well conserved. Analysis of the hydropathy profiles has suggested that the glutamate transporters have a global structure that is unique among secondary transporters. Experimentally, the unique structure of the transporters was recently confirmed by membrane topology studies. Although there is still controversy about part of the topology, the most likely model predicts the presence of eight membrane-spanning α-helices and a loop-pore structure which is unique among secondary transporters but may resemble loop-pores found in ion channels. A second distinctive structural feature is the presence of a highly amphipathic membrane-spanning helix that provides a hydrophilic path through the membrane. Recent data from analysis of site-directed mutants and studies on the mechanism and pharmacology of the transporters are discussed in relation to the structural model.

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ACE2 and gut amino acid transport

Clinical Science ◽

10.1042/cs20200477 ◽

2020 ◽

Vol 134 (21) ◽

pp. 2823-2833 ◽

Cited By ~ 2

Author(s):

Simone M.R. Camargo ◽

Raphael N. Vuille-dit-Bille ◽

Chantal F. Meier ◽

François Verrey

Keyword(s):

Amino Acids ◽

Small Intestine ◽

Amino Acid ◽

Amino Acid Transporter ◽

Neutral Amino Acid ◽

Amino Acid Transporters ◽

Type I ◽

Small Intestinal Mucosa ◽

Neutral Amino Acid Transporter ◽

Acid Transporter

Abstract ACE2 is a type I membrane protein with extracellular carboxypeptidase activity displaying a broad tissue distribution with highest expression levels at the brush border membrane (BBM) of small intestine enterocytes and a lower expression in stomach and colon. In small intestinal mucosa, ACE2 mRNA expression appears to increase with age and to display higher levels in patients taking ACE-inhibitors (ACE-I). There, ACE2 protein heterodimerizes with the neutral amino acid transporter Broad neutral Amino acid Transporter 1 (B0AT1) (SLC6A19) or the imino acid transporter Sodium-dependent Imino Transporter 1 (SIT1) (SLC6A20), associations that are required for the surface expression of these transport proteins. These heterodimers can form quaternary structures able to function as binding sites for SARS-CoV-2 spike glycoproteins. The heterodimerization of the carboxypeptidase ACE2 with B0AT1 is suggested to favor the direct supply of substrate amino acids to the transporter, but whether this association impacts the ability of ACE2 to mediate viral infection is not known. B0AT1 mutations cause Hartnup disorder, a condition characterized by neutral aminoaciduria and, in some cases, pellagra-like symptoms, such as photosensitive rash, diarrhea, and cerebellar ataxia. Correspondingly, the lack of ACE2 and the concurrent absence of B0AT1 expression in small intestine causes a decrease in l-tryptophan absorption, niacin deficiency, decreased intestinal antimicrobial peptide production, and increased susceptibility to inflammatory bowel disease (IBD) in mice. Thus, the abundant expression of ACE2 in small intestine and its association with amino acid transporters appears to play a crucial role for the digestion of peptides and the absorption of amino acids and, thereby, for the maintenance of structural and functional gut integrity.

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Na+-dependent neutral amino acid transporters A, ASC, and N of the blood-brain barrier: mechanisms for neutral amino acid removal

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00187.2004 ◽

2004 ◽

Vol 287 (4) ◽

pp. E622-E629 ◽

Cited By ~ 32

Author(s):

Robyn L. O'Kane ◽

Juan R. Viña ◽

Ian Simpson ◽

Richard A. Hawkins

Keyword(s):

Amino Acid ◽

Blood Brain Barrier ◽

Functional Organization ◽

Extracellular Fluid ◽

Neutral Amino Acid ◽

Brain Barrier ◽

Amino Acid Transporters ◽

System A ◽

Blood Brain ◽

Voltage Dependent

Four Na+-dependent transporters of neutral amino acids (NAA) are known to exist in the abluminal membranes (brain side) of the blood-brain barrier (BBB). This article describes the kinetic characteristics of systems A, ASC, and N that, together with the recently described Na+-dependent system for large NAA (Na+-LNAA), provide a basis for understanding the functional organization of the BBB. The data demonstrate that system A is voltage dependent (3 positive charges accompany each molecule of substrate). Systems ASC and N are not voltage dependent. Each NAA is a putative substrate for at least one system, and several NAA are transported by as many as three. System A transports Pro, Ala, His, Asn, Ser, and Gln; system ASC transports Ser, Gly, Met, Val, Leu, Ile, Cys, and Thr; system N transports Gln, His, Ser, and Asn; Na+-LNAA transports Leu, Ile, Val, Trp, Tyr, Phe, Met, Ala, His, Thr, and Gly. Together, these four systems have the capability to actively transfer every naturally occurring NAA from the extracellular fluid (ECF) to endothelial cells and thence to the circulation. The existence of facilitative transport for NAA (L1) on both membranes provides the brain access to essential NAA. The presence of Na+-dependent carriers on the abluminal membrane provides a mechanism by which NAA concentrations in the ECF of brain are maintained at ∼10% of those of the plasma.

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The effects of maternal nutrient restriction and day of early pregnancy on the location and abundance of neutral amino acid transporters in beef heifer utero-placental tissues

Journal of Animal Science ◽

10.1093/jas/skaa197 ◽

2020 ◽

Vol 98 (7) ◽

Cited By ~ 1

Author(s):

Matthew S Crouse ◽

Kyle J McLean ◽

Nathaniel P Greseth ◽

Alison K Ward ◽

Lawrence P Reynolds ◽

...

Keyword(s):

Amino Acid ◽

Cross Sections ◽

Maternal Nutrition ◽

Placental Tissue ◽

Neutral Amino Acid ◽

Tissue Type ◽

Fetal Membrane ◽

Amino Acid Transporters ◽

Randomized Design ◽

Beef Heifer

Abstract We hypothesized that maternal nutrition and day of gestation would influence the abundance of the neutral amino acid transporters SLC1A1, SLC1A5, SLC7A5, SLC38A2, and SLC38A7 in heifer utero-placental tissues. Angus-cross heifers (n = 43) were estrus synchronized and bred via AI. At breeding, heifers were assigned to one of two dietary intake groups (CON = 100% of requirements to achieve 0.45 kg/d gain or restricted heifers (RES) = 60% of CON intake) and ovariohysterectomized on day 16, 34, or 50 of gestation (n = 6 to 9/d). Thus, the experimental design was a completely randomized design with a 2 × 3 factorial arrangement of treatments. Uterine cross sections were taken from the horn ipsilateral to the CL, fixed in 10% NBF, sectioned at 5 µm, and stained for transporters. For each image, the areas of fetal membrane (FM; chorioallantois), endometrium (ENDO), superficial glands (SG), deep glands (DG), and myometrium (MYO) were analyzed separately for relative intensity of fluorescence as an indicator of transporter abundance. Analysis of FM was only conducted on days 34 and 50. In ENDO, SLC7A5 was greater (P < 0.01) in CON compared with RES heifers. In SG, SLC1A1 was greater (P = 0.02) in day 16 RES compared with day 16 CON and days 34 and 50 RES. In DG, SLC1A1 was greater (P = 0.02) on day 16 compared with 50 of gestation. In MYO, SLC1A1 was greater (P = 0.02) in day 50 CON compared with day 16 CON and day 50 RES. Additionally, in MYO SLC38A2 was greater (P = 0.02) in day 16 RES compared with day 16 CON and day 34 RES. In FM, SLC7A5 tended (P = 0.08) to be greater in CON vs RES. Analysis of all uterine tissues on day 16 determined that expression of SLC1A1, SLC1A5, SL38A2, and SL38A7 differed across uterine tissue type (P < 0.01); however, only SLC7A5 tended (P = 0.10) to differ and be greater in CON compared with RES heifers. Analysis of all utero-placental tissues on days 34 and 50 determined that SLC1A1, SLC7A5, SLC38A2, and SLC38A7 were greater (P ≤ 0.03) in CON compared with RES heifers. Furthermore, abundance of all transporters investigated on days 34 and 50 differed across utero-placental tissue types (P < 0.01). These data support our hypothesis that maternal nutrition and day of gestation influence the abundance of neutral amino acid transporters in utero-placental tissues from days 16 to 50 of gestation. Additionally, these data combined with previously published works help further elucidate nutrient supply and demands of the maternal and fetal system during early gestation in beef heifers.

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