1
|
Anderson CMH, Edwards N, Watson AK, Althaus M, Thwaites DT. Reshaping the Binding Pocket of the Neurotransmitter:Solute Symporter (NSS) Family Transporter SLC6A14 (ATB 0,+) Selectively Reduces Access for Cationic Amino Acids and Derivatives. Biomolecules 2022; 12:biom12101404. [PMID: 36291613 PMCID: PMC9599917 DOI: 10.3390/biom12101404] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Revised: 09/25/2022] [Accepted: 09/29/2022] [Indexed: 11/16/2022] Open
Abstract
SLC6A14 (ATB0,+) is unique among SLC proteins in its ability to transport 18 of the 20 proteinogenic (dipolar and cationic) amino acids and naturally occurring and synthetic analogues (including anti-viral prodrugs and nitric oxide synthase (NOS) inhibitors). SLC6A14 mediates amino acid uptake in multiple cell types where increased expression is associated with pathophysiological conditions including some cancers. Here, we investigated how a key position within the core LeuT-fold structure of SLC6A14 influences substrate specificity. Homology modelling and sequence analysis identified the transmembrane domain 3 residue V128 as equivalent to a position known to influence substrate specificity in distantly related SLC36 and SLC38 amino acid transporters. SLC6A14, with and without V128 mutations, was heterologously expressed and function determined by radiotracer solute uptake and electrophysiological measurement of transporter-associated current. Substituting the amino acid residue occupying the SLC6A14 128 position modified the binding pocket environment and selectively disrupted transport of cationic (but not dipolar) amino acids and related NOS inhibitors. By understanding the molecular basis of amino acid transporter substrate specificity we can improve knowledge of how this multi-functional transporter can be targeted and how the LeuT-fold facilitates such diversity in function among the SLC6 family and other SLC amino acid transporters.
Collapse
Affiliation(s)
- Catriona M. H. Anderson
- School of Natural & Environmental Sciences, Faculty of Science, Engineering & Agriculture, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
- Correspondence: (C.M.H.A.); (D.T.T.)
| | - Noel Edwards
- Biosciences Institute, Faculty of Medical Sciences, Framlington Place, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Andrew K. Watson
- Biosciences Institute, Faculty of Medical Sciences, Framlington Place, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Mike Althaus
- School of Natural & Environmental Sciences, Faculty of Science, Engineering & Agriculture, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
- Department of Natural Sciences & Institute for Functional Gene Analytics, Bonn-Rhein-Sieg University of Applied Sciences, 53359 Rheinbach, Germany
| | - David T. Thwaites
- Biosciences Institute, Faculty of Medical Sciences, Framlington Place, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
- Correspondence: (C.M.H.A.); (D.T.T.)
| |
Collapse
|
2
|
Park YJ, Oh TS, Jang MJ. Effect of adding amino acids on the production of Gamma-Aminobutyric Acid (GABA) by mycelium of Lentinula edodes. INTERNATIONAL JOURNAL OF FOOD ENGINEERING 2019. [DOI: 10.1515/ijfe-2018-0287] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractThis study was carried out to investigate the production of a health functional food component through the production of GABA by mycelium of Lentinula edodes (LE) cultured in a medium containing four different amino acids. To confirm the GABA content in the medium, the amount of GABA produced by adding 0.1 M of glutamic acid, alanine, glycine, or lysine to Potato Dextrose Agar (PDA) medium and Potato Dextrose Broth (PDB) medium was determined. The amount of mycelia in the PDB medium was 4.85 g/L in the amino acid-free medium, 5.12 g/L in the glutamic acid medium, 4.63 g/L in the alanine medium, 4.87 g/L in the glycine medium, and 4.18 g/L in the lysine medium. The amount of amino acid added to the medium did not interfere with the normal growth of LE because the amount of excess amino acid was not significantly different from that of the control. The GABA content was 10.35 mg/L in the control (amino acid-free), 30.29 mg/L in the glutamic acid supplemented medium, 11.70 mg/L in the alanine supplemented medium, 10.62 mg/L in the glycine supplemented medium and 3.96 mg/L in Lysine supplemented medium. These results show that the excess glutamic acid had the highest level of GABA in the mushroom culture medium. On the other hand, it was confirmed that the addition of excess alanine and glycine did not affect the GABA production compared to the control. These results suggest that continuous GABA production could not be achieved by using an ion exchange resin after the disruption of GABA production by biological methods, however, continuous GABA production using the mycelium of LE is possible in this study.
Collapse
Affiliation(s)
- Youn-Jin Park
- Green Manure and Legumes Resource Center, Plant resources, Kongju National UniversityYesan, Korea (Republic of)
- Plant Resources, Kongju National University, Gongju, Korea (the Republic of)
| | - Tae-Seok Oh
- Plant Resources, Kongju National University, Gongju, Korea (the Republic of)
| | - Myoung-Jun Jang
- Plant Resources, Kongju National University, Yesan, Korea (Republic of)
- Plant Resources, Kongju National University, Gongju, Korea (the Republic of)
| |
Collapse
|
3
|
Abstract
The small intestine mediates the absorption of amino acids after ingestion of protein and sustains the supply of amino acids to all tissues. The small intestine is an important contributor to plasma amino acid homeostasis, while amino acid transport in the large intestine is more relevant for bacterial metabolites and fluid secretion. A number of rare inherited disorders have contributed to the identification of amino acid transporters in epithelial cells of the small intestine, in particular cystinuria, lysinuric protein intolerance, Hartnup disorder, iminoglycinuria, and dicarboxylic aminoaciduria. These are most readily detected by analysis of urine amino acids, but typically also affect intestinal transport. The genes underlying these disorders have all been identified. The remaining transporters were identified through molecular cloning techniques to the extent that a comprehensive portrait of functional cooperation among transporters of intestinal epithelial cells is now available for both the basolateral and apical membranes. Mouse models of most intestinal transporters illustrate their contribution to amino acid homeostasis and systemic physiology. Intestinal amino acid transport activities can vary between species, but these can now be explained as differences of amino acid transporter distribution along the intestine. © 2019 American Physiological Society. Compr Physiol 9:343-373, 2019.
Collapse
Affiliation(s)
- Stefan Bröer
- Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia
| | - Stephen J Fairweather
- Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia
| |
Collapse
|
4
|
Gookin JL, Stauffer SH, Stone MR. Induction of arginase II by intestinal epithelium promotes the uptake of L-arginine from the lumen of Cryptosporidium parvum-infected porcine ileum. J Pediatr Gastroenterol Nutr 2008; 47:417-27. [PMID: 18852633 PMCID: PMC3685577 DOI: 10.1097/mpg.0b013e31816f6c02] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
OBJECTIVES To determine the specific transport system activities and expression of transporter genes responsible for uptake of L-arginine from the lumen of normal and Cryptosporidium parvum-infected neonatal porcine ileum and the influence of L-arginine catabolic pathways on L-arginine uptake. METHODS Intact sheets of ileal mucosa from control and C parvum-infected neonatal piglets were mounted in Ussing chambers and the uptake of 14C-L-arginine was determined under initial rate conditions and in the presence of transport system-selective inhibitors. Epithelial expression of L-arginine transporter genes was quantified by real-time reverse transcription polymerase chain reaction. L-Arginine catabolic enzyme expression was examined by immunoblotting epithelial lysates for arginase I and II. The role of intracellular catabolism in promoting the uptake of L-arginine was determined by pharmacological inhibition of nitric oxide synthase and arginase activities. RESULTS C parvum-infected ileum transported L-arginine at rates equivalent to uninfected epithelium despite profound villous atrophy. This was attributed to enhanced uptake of L-arginine by individual epithelial cells in the infection. There were no differences in L-arginine transport system activities (y(+) and B(0, +)) or level of transporter gene expression (CAT-1, CAT-2A, and ATB(0, +)) between uninfected and C parvum-infected epithelial cells. However, infected epithelia had induced expression of the L-arginine hydrolytic enzyme arginase II and lower concentrations of L-arginine. Furthermore, transport of L-arginine by the infected epithelium was significantly inhibited by pharmacological blockade of arginase. CONCLUSIONS Intracellular catabolism by arginase II, the induction of which has not been described previously for intestinal epithelium, facilitates uptake of L-arginine by infected epithelium using transport systems that do not differ from those of uninfected cells. Induction of arginase II may limit nitric oxide synthesis by competing with nitric oxide synthase for utilization of L-arginine or promote use of L-arginine for the synthesis of reparative polyamines.
Collapse
Affiliation(s)
- Jody L Gookin
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA.
| | | | | |
Collapse
|
5
|
Abstract
The beta-alanine carrier was characterized functionally in the 1960s to 1980s at the luminal surface of the ileal mucosal wall and is a Na(+)- and Cl(-)-dependent transporter of a number of essential and non-essential cationic and dipolar amino acids including lysine, arginine and leucine. beta-Alanine carrier-like function has not been demonstrated by any solute carrier transport system identified at the molecular level. A series of experiments were designed to determine whether solute carrier SLC6A14 is the molecular correlate of the intestinal beta-alanine carrier, perhaps the last of the classical intestinal amino acid transport systems to be identified at the molecular level. Following expression of the human SLC6A14 transporter in Xenopus laevis oocytes, the key functional characteristics of the beta-alanine carrier, identified previously in situ in ileum, were demonstrated for the first time. The transport system is both Na(+) and Cl(-) dependent, can transport non-alpha-amino acids such as beta-alanine with low affinity, and has a higher affinity for dipolar and cationic amino acids such as leucine and lysine. N-methylation of its substrates reduces the affinity for transport. These observations confirm the hypothesis that the SLC6A14 gene encodes the transport protein known as the beta-alanine carrier which, due to its broad substrate specificity, is likely to play an important role in absorption of essential nutrients and drugs in the distal regions of the human gastrointestinal tract.
Collapse
Affiliation(s)
- Catriona M H Anderson
- Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK
| | | | | |
Collapse
|
6
|
Bröer S. Amino acid transport across mammalian intestinal and renal epithelia. Physiol Rev 2008; 88:249-86. [PMID: 18195088 DOI: 10.1152/physrev.00018.2006] [Citation(s) in RCA: 632] [Impact Index Per Article: 39.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The transport of amino acids in kidney and intestine is critical for the supply of amino acids to all tissues and the homeostasis of plasma amino acid levels. This is illustrated by a number of inherited disorders affecting amino acid transport in epithelial cells, such as cystinuria, lysinuric protein intolerance, Hartnup disorder, iminoglycinuria, dicarboxylic aminoaciduria, and some other less well-described disturbances of amino acid transport. The identification of most epithelial amino acid transporters over the past 15 years allows the definition of these disorders at the molecular level and provides a clear picture of the functional cooperation between transporters in the apical and basolateral membranes of mammalian epithelial cells. Transport of amino acids across the apical membrane not only makes use of sodium-dependent symporters, but also uses the proton-motive force and the gradient of other amino acids to efficiently absorb amino acids from the lumen. In the basolateral membrane, antiporters cooperate with facilitators to release amino acids without depleting cells of valuable nutrients. With very few exceptions, individual amino acids are transported by more than one transporter, providing backup capacity for absorption in the case of mutational inactivation of a transport system.
Collapse
Affiliation(s)
- Stefan Bröer
- School of Biochemistry and Molecular Biology, Australian National University, Canberra, Australian Capital Territory, Australia.
| |
Collapse
|
7
|
Bröer A, Cavanaugh JA, Rasko JEJ, Bröer S. The molecular basis of neutral aminoacidurias. Pflugers Arch 2005; 451:511-7. [PMID: 16052352 DOI: 10.1007/s00424-005-1481-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2005] [Accepted: 06/09/2005] [Indexed: 10/25/2022]
Abstract
Recent success in the molecular cloning and identification of apical neutral amino acid transporters has shed a new light on inherited neutral amino acidurias, such as Hartnup disorder and Iminoglycinuria. Hartnup disorder is caused by mutations in the neutral amino acid transporter B(0) AT1 (SLC6A19). The transporter is found in kidney and intestine, where it is involved in the resorption of all neutral amino acids. The molecular defect underlying Iminoglycinuria has not yet been identified. However, two transporters, the proton amino acid transporter PAT1 (SLC36A1) and the IMINO transporter (SLC6A20) appear to play key roles in the resorption of glycine and proline. A model is presented, involving all three transporters that can explain the phenotypic variability of iminoglycinuria.
Collapse
Affiliation(s)
- Angelika Bröer
- School of Biochemistry and Molecular Biology, Australian National University, Canberra
| | | | | | | |
Collapse
|
8
|
Sloan JL, Grubb BR, Mager S. Expression of the amino acid transporter ATB 0+ in lung: possible role in luminal protein removal. Am J Physiol Lung Cell Mol Physiol 2003; 284:L39-49. [PMID: 12388375 DOI: 10.1152/ajplung.00164.2002] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Normal lung function requires transepithelial clearance of luminal proteins; however, little is known about the molecular mechanisms of protein transport. Protein degradation followed by transport of peptides and amino acids may play an important role in this process. We previously cloned and functionally characterized the neutral and cationic amino acid transporter ATB(0+) and showed expression in the lung by mRNA analysis. In this study, the tissue distribution, subcellular localization, and function of the transporter in native tissue were investigated. Western blots showed expression of the ATB(0+) protein in mouse lung, stomach, colon, testis, blastocysts, and human lung. Immunohistochemistry revealed that ATB(0+) is predominantly expressed on the apical membrane of ciliated epithelial cells throughout mouse airways from trachea to bronchioles and in alveolar type I cells. Electrical measurements from mouse trachea preparations showed Na(+)- and Cl(-)-dependent, amino acid-induced short-circuit current consistent with the properties of ATB(0+). We hypothesize that, by removing amino acids from the airway lumen, the transporter contributes to protein clearance and, by maintaining a low nutrient environment, plays a role in lung defense.
Collapse
Affiliation(s)
- Jennifer L Sloan
- Department of Cell and Molecular Physiology and the Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC 27599, USA
| | | | | |
Collapse
|
9
|
Tunnicliff G. Membrane glycine transport proteins. J Biomed Sci 2003; 10:30-6. [PMID: 12566983 DOI: 10.1007/bf02255994] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2002] [Accepted: 09/01/2002] [Indexed: 11/24/2022] Open
Abstract
Structurally, the simplest amino acid is glycine, and it has a number of important yet distinct functions in the body. This review focuses on the different transport systems and the associated carrier proteins for glycine that are responsible for its movement across biological membranes. Transport proteins in the class GLYT appear to be the most specific for glycine. However, the B0+ system also carries significant amounts of glycine. Other amino acid transport systems capable of carrying small amounts of glycine are ASC, asc and system L. In addition, an ATP-dependent transport process exists that takes up glycine into synaptic vesicles at nerve endings. This is known as the vesicular inhibitory amino acid transporter since, in addition to glycine, it can transport possibly two other inhibitory neurotransmitters.
Collapse
Affiliation(s)
- Godfrey Tunnicliff
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Evansville, Ind. 47712, USA.
| |
Collapse
|
10
|
Bogé G, Roche H, Balocco C. Amino acid transport by intestinal brush border vesicles of a marine fish, Boops salpa. Comp Biochem Physiol B Biochem Mol Biol 2002; 131:19-26. [PMID: 11742754 DOI: 10.1016/s1096-4959(01)00474-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The transport of glycine, alanine, methionine and alpha amino-isobutyric acid (AIB) was studied on brush border membrane vesicles of Boops salpa, a marine fish. This transport was Na(+)-, Cl(-)- and pH-dependent. In the presence of NaCl, the uptake decreased as the pH increased from 5.5 to 8.5. With Na2SO4, the transport of the four amino acids was strongly reduced and the pH optimum was 7-8. In the presence of NaCl, amino acid transport was described by high and low affinity kinetics. The K(t) of the high-affinity component was comparable for glycine, alanine and methionine (0.1 mM), and was significantly enhanced for AIB (0.6 mM). The J(max) of the low affinity component was significantly lower for methionine and AIB than for glycine and alanine. Lowering the sodium concentration from 80 to 20 mM significantly increased K(t) and J(max) of the high-affinity component of glycine transport. Moreover, the kinetics of AIB transport under 100 mM Na(+) were similar to glycine kinetics under 40 mM Na(+) and the two amino acids competed for the same carrier(s). These results suggest that chloride ions are essential in neutral amino acid transport in Boops, that multiple saturable components are involved in this process, and that sodium plays an important role in the differences between the transport kinetics of amino acids.
Collapse
Affiliation(s)
- Gérard Bogé
- Université de Toulon, LEPI and Département de Génie Biologique, BP 132, F-83957 Cedex, La Garde, France.
| | | | | |
Collapse
|
11
|
Ugawa S, Sunouchi Y, Ueda T, Takahashi E, Saishin Y, Shimada S. Characterization of a mouse colonic system B(0+) amino acid transporter related to amino acid absorption in colon. Am J Physiol Gastrointest Liver Physiol 2001; 281:G365-70. [PMID: 11447016 DOI: 10.1152/ajpgi.2001.281.2.g365] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Previous experiments have shown that an amino acid transport system B(0+) transporter in cultured colonic epithelial cells mediates amino acid absorption. Here we describe the cloning and functional characterization of a system B(0+) transporter selectively expressed in the colon. Using the combination of an expressed sequence tag database search and RT-PCR approaches, we cloned a mouse colonic amino acid transporter, designated mCATB(0+). Northern blot analysis revealed that mCATB(0+) was selectively expressed in the large intestine. In situ hybridization showed the mCATB(0+) mRNA to be localized in absorptive epithelial cells. When expressed in Xenopus oocytes, mCATB(0+) exhibited a Na(+)-dependent stereoselective uptake and a broad specificity for neutral and cationic amino acids, which is characteristic of amino acid transport system B(0+). In vivo [(3)H]glycine uptake assay demonstrated that a system B(0+)-like transporter protein was expressed on the apical surface of the colonic absorptive cells. Our data suggest that a mouse colonic amino acid transporter mCATB(0+) may absorb amino acids from the intestinal contents in the colon.
Collapse
Affiliation(s)
- S Ugawa
- Department of Anatomy II, Nagoya City University Medical School, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan
| | | | | | | | | | | |
Collapse
|
12
|
Avissar NE, Ziegler TR, Wang HT, Gu LH, Miller JH, Iannoli P, Leibach FH, Ganapathy V, Sax HC. Growth factors regulation of rabbit sodium-dependent neutral amino acid transporter ATB0 and oligopeptide transporter 1 mRNAs expression after enteretomy. JPEN J Parenter Enteral Nutr 2001; 25:65-72. [PMID: 11284472 DOI: 10.1177/014860710102500265] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND Sucessful intestinal adaptation after massive enterectomy is dependent on increased efficiency of nutrient transport. However, midgut resection (MGR) in rabbits induces an initial decrease in sodium-dependent brush border neutral amino acid transport, whereas parenteral epidermal growth factor (EGF) and growth hormone (GH) reverse this downregulation. We investigated intestinal amino acid transporter B0 (ATB0) and oligopeptide transporter 1 (PEPT 1) mRNA expression after resection and in response to EGF and/or GH. METHODS Rabbits underwent anesthesia alone (control) or proximal, midgut, and distal resections. Full-thickness intestine was harvested from all groups on postoperative day (POD) 7, and on POD 14 from control and MGR rabbits. A second group of MGR rabbits received EGF and/or GH for 7 days, beginning 7 days after resection. ATB0 and PEPT 1 mRNA levels were determined by Northern blot analysis. RESULTS In control animals, ileal ATB0 mRNA abundance was three times higher than jejunal mRNA, whereas PEPT 1 mRNA expression was similar. By 7 and 14 days after MGR, jejunal ATB0 mRNA abundance was decreased by 50% vs control jejunum. A 50% decrease in jejunal PEPT 1 message was delayed until 14 days after MGR. Treatment with EGF plus GH did not alter ATB0 mRNA expression but doubled PEPT 1 mRNA in the jejunum. CONCLUSION The site of resection, time postresection, and growth factors treatment differentially influence ATB0 and PEPT 1 mRNA expression. Enhanced sodium-dependent brush border neutral amino acid transport with GH plus EGF administration is independent of increased ATB0 mRNA expression in rabbit small intestine after enterectomy.
Collapse
Affiliation(s)
- N E Avissar
- Department of Surgery, University of Rochester Medical Center, New York 14642-8410, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Munck LK, Grondahl ML, Thorboll JE, Skadhauge E, Munck BG. Transport of neutral, cationic and anionic amino acids by systems B, b(o,+), X(AG), and ASC in swine small intestine. Comp Biochem Physiol A Mol Integr Physiol 2000; 126:527-37. [PMID: 10989343 DOI: 10.1016/s1095-6433(00)00227-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Amino acid influx across the brush border membrane of the intact pig ileal epithelium was studied. It was examine whether in addition to system B, systems ASC and b(o,+) were involved in transport of bipolar amino acids. The kinetics of interactions between lysine and leucine demonstrates that system b(o,+) is present and accessible also to L-glutamine. D-aspartate (K(1/2) 0.3 mM) and L-glutamate (K(i) 0.5 mM) share a high affinity transporter with a maximum rate of 1.3 micromol cm(-2) h(-1), while only L-glutamate with a K(1/2) of 14.4 mM uses a low affinity transporter with a maximum rate of 2. 7 micromol cm(-2) h(-1), system ASC, against which serine has a K(i) of 1.6 mM. In the presence of 100 mM lysine, L-glutamine (A), leucine (B), and methionine (C) fulfilled the criteria of the ABC test for transport by one and the same transporter. However, serine inhibits not only transport of L-glutamate but also of glutamine (K(i) 0.5 mM), and L-glutamate inhibits part of the transport of glutamine. The test does, therefore, only indicate that the three bipolar amino acids have similar affinities for transport by systems B and ASC. Further study of the function of system B must be carried out under full inhibition by lysine and glutamate.
Collapse
Affiliation(s)
- L K Munck
- Department of Internal Medicine, Koge Hospital, DK-4600, Koge, Denmark.
| | | | | | | | | |
Collapse
|
14
|
Abstract
BeWo choriocarcinoma cells were cultured onto solid microcarrier beads, packed into columns and superfused. Unidirectional influx of l -phenylalanine (l -phe) and l -leucine (l -leu) across the microvillous border of the cells was studied using a rapid paired-tracer dilution technique. Influx of l -phe and l -leu comprised both saturable and non-saturable components. K(m)values for l -phe and l -leu were 0.57+/-0.01 m m and 0.05+/-0.01 m m, respectively, with V(max)values of 120.4+/-0.5 nmol/mg/min and 41. 7+/-0.2 nmol/mg/min. Non-saturable uptake components were 29.0+/-0.1 nmol/mg/m m and 37.9+/-0.1 nmol/mg/min/m m respectively. l -leu uptake was found to be sodium-independent. The uptake of l -[(3)H]phe was strongly inhibited (90-100 per cent) by unlabelled l -phe, d -phe, l -leu or 2-aminoendobicyclo-[2,2, 1]-heptane-2-carboxylic acid (BCH) but not by l -arginine (l -arg) or methyl alpha-aminoisobutric acid (Me-AIB). Pre-incubation of Bewo cultures for 24 h in the presence of an additional 1.2 m ml -phe (simulating maternal phenylketonuria) significantly reduced both the K(m)and V(max)components of l -phe influx. l -arg (2 m m) had no effect on l -leu influx whereas 2 m ml -phe completely inhibited saturable l -leu influx. These data suggest that the microvillous border of differentiated BeWo cells transport large neutral amino acids predominantly via system L rather than by B(0) or y(+)L transporters.
Collapse
Affiliation(s)
- B M Eaton
- Department of Maternal and Fetal Medicine, Imperial College School of Medicine, Chelsea and Westminster Hospital, London, UK.
| | | |
Collapse
|
15
|
Ganapathy V, Ganapathy ME, Leibach FH. Chapter 10 Intestinal transport of peptides and amino acids. CURRENT TOPICS IN MEMBRANES 2000. [DOI: 10.1016/s1063-5823(00)50012-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
|
16
|
Sloan JL, Mager S. Cloning and functional expression of a human Na(+) and Cl(-)-dependent neutral and cationic amino acid transporter B(0+). J Biol Chem 1999; 274:23740-5. [PMID: 10446133 DOI: 10.1074/jbc.274.34.23740] [Citation(s) in RCA: 252] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A Na(+)-dependent neutral and cationic amino acid transport system (B(0+)) plays an important role in many cells and tissues; however, the molecular basis for this transport system is still unknown. To identify new transporters, the expressed sequence tag database was queried, and cDNA fragments with sequence similarity to the Na(+)/Cl(-)-dependent neurotransmitter transporter family were identified. Based on these sequences, rapid amplification of cDNA ends of human mammary gland cDNA was used to obtain a cDNA of 4.5 kilobases (kb). The open reading frame encodes a 642-amino acid protein named amino acid transporter B(0+). Human ATB(0+) (hATB(0+)) is a novel member of the Na(+)/Cl(-)-dependent neurotransmitter transporter family with the highest sequence similarity to the glycine and proline transporters. Northern blot analysis identified transcripts of approximately 4.5 kb and approximately 2 kb in the lung. Another tissue survey suggests expression in the trachea, salivary gland, mammary gland, stomach, and pituitary gland. Electrophysiology and radiolabeled amino acid uptake measurements were used to functionally characterize the transporter expressed in Xenopus oocytes. hATB(0+) was found to transport both neutral and cationic amino acids, with the highest affinity for hydrophobic amino acids and the lowest affinity for proline. Amino acid transport was Na(+) and Cl(-)-dependent and was attenuated in the presence of 2-aminobicyclo-[2.2.1]-heptane-2-carboxylic acid, a system B(0+) inhibitor. These characteristics are consistent with system B(0+) amino acid transport. Thus, hATB(0+) is the first cloned B(0+) amino acid transporter.
Collapse
Affiliation(s)
- J L Sloan
- Department of Cell and Molecular Physiology and the Curriculum in Neurobiology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | | |
Collapse
|
17
|
Devés R, Boyd CA. Transporters for cationic amino acids in animal cells: discovery, structure, and function. Physiol Rev 1998; 78:487-545. [PMID: 9562037 DOI: 10.1152/physrev.1998.78.2.487] [Citation(s) in RCA: 346] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The structure and function of the four cationic amino acid transporters identified in animal cells are discussed. The systems differ in specificity, cation dependence, and physiological role. One of them, system y+, is selective for cationic amino acids, whereas the others (B[0,+], b[0,+], and y+ L) also accept neutral amino acids. In recent years, cDNA clones related to these activities have been isolated. Thus two families of proteins have been identified: 1) CAT or cationic amino acid transporters and 2) BAT or broad-scope transport proteins. In the CAT family, three genes encode for four different isoforms [CAT-1, CAT-2A, CAT-2(B) and CAT-3]; these are approximately 70-kDa proteins with multiple transmembrane segments (12-14), and despite their structural similarity, they differ in tissue distribution, kinetics, and regulatory properties. System y+ is the expression of the activity of CAT transporters. The BAT family includes two isoforms (rBAT and 4F2hc); these are 59- to 78-kDa proteins with one to four membrane-spanning segments, and it has been proposed that these proteins act as transport regulators. The expression of rBAT and 4F2hc induces system b[0,+] and system y+ L activity in Xenopus laevis oocytes, respectively. The roles of these transporters in nutrition, endocrinology, nitric oxide biology, and immunology, as well as in the genetic diseases cystinuria and lysinuric protein intolerance, are reviewed. Experimental strategies, which can be used in the kinetic characterization of coexpressed transporters, are also discussed.
Collapse
Affiliation(s)
- R Devés
- Programa de Fisiología y Biofísica, Instituto de Ciencias Biomédicas, Universidad de Chile, Santiago
| | | |
Collapse
|
18
|
Yao SY, Muzyka WR, Elliott JF, Cheeseman CI, Young JD. Cloning and functional expression of a cDNA from rat jejunal epithelium encoding a protein (4F2hc) with system y+L amino acid transport activity. Biochem J 1998; 330 ( Pt 2):745-52. [PMID: 9480885 PMCID: PMC1219200 DOI: 10.1042/bj3300745] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Two different protein families, designated CAT (cationic amino acid transporter) and BAT (broad-specificity amino acid transporter) mediate the plasma membrane transport of cationic amino acids in animal cells. CAT transporters have 12-14 transmembrane domains and are selective for cationic amino acids. BAT proteins, in contrast, have one to four transmembrane domains and induce the transport of both cationic and zwitterionic amino acids when expressed in Xenopus oocytes. Mutations in the human BAT gene cause type I cystinuria, a disease affecting the ability of intestinal and renal brush border membranes to transport cationic amino acids and cystine. We have used functional expression cloning in oocytes to isolate a BAT-related cDNA from rat jejunal epithelium. The cDNA encodes the rat 4F2 heavy chain (4F2hc) cell-surface antigen, a 527-residue (60 kDa) protein that is 26% identical in amino acid sequence with rat renal BAT (also known as NBAT/D2). Expression of rat jejunal 4F2hc in oocytes induced the lysine-inhibitable Na+-dependent influx of leucine and the leucine-inhibitable Na+-independent influx of lysine. Lysine efflux was stimulated by extracellular (Na+ plus leucine). These characteristics identify the expressed amino acid transport activity as system y+L, a transporter that has been implicated in basal membrane transport of cationic amino acids in intestine, kidney and placenta.
Collapse
Affiliation(s)
- S Y Yao
- Membrane Transport Research Group, Department of Physiology, Medical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | | | | | | | | |
Collapse
|
19
|
Munck LK. Comparative aspects of chloride-dependent amino acid transport across the brush-border membrane of mammalian small intestine. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART A, PHYSIOLOGY 1997; 118:229-31. [PMID: 9366049 DOI: 10.1016/s0300-9629(97)00072-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Chloride-dependent amino acid transport has been described in several tissues. This article briefly reviews the evidence of cotransport of chloride and amino acids across the brush-border membrane of rabbit distal ileum. On the basis of amino acid carriers described in the rabbit and the surveys of chloride-dependence reported, a comparison of amino acid carriers in the mammalian small intestine is performed. Additional characteristics of the carriers in the different species are included in the discussion when necessary. From this comparison the rabbit distal ileum and the pig small intestine emerge as the best models of amino acid transport in the human small intestine.
Collapse
Affiliation(s)
- L K Munck
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark
| |
Collapse
|
20
|
Munck LK, Grøndahl ML, Skadhauge E. beta-Amino acid transport in pig small intestine in vitro by a high-affinity, chloride-dependent carrier. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1238:49-56. [PMID: 7654750 DOI: 10.1016/0005-2736(95)00107-e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
This study describes unidirectional influx of amino acids and D-glucose across the small intestinal brush-border membrane of fully weaned eight week old pigs. Influx is minimal in the duodenum and maximal in the distal and/or mid small intestine. Influx of beta-alanine, taurine and N-methyl-aminoisobutyric acid is chloride-dependent. The activation stoichiometry for taurine influx is 1.0 +/- 0.2 chloride/2.4 +/- 0.3 sodium/1 taurine. Influx of D-glucose, lysine, glycine and glutamate is chloride-independent. An ABC test demonstrates a common beta-amino acid carrier: (a) the apparent affinity constant K1/2Taurine is 44 +/- 13 microM (means +/- S.D.) and the inhibitory constant (KiTaurine) against beta-alanine influx is 41 +/- 5 microM (means +/- S.E.). (b) K1/2beta-alanine is 97 +/- 23 microM and Kibeta-alanine against taurine influx is 160 +/- 22 microM. (c) KiHypotaurine against taurine and beta-alanine influx is 43 +/- 4 (n = 7) and 22 +/- 5 microM (n = 7), respectively. In conclusion, a high affinity, low capacity, sodium- and chloride-dependent carrier of beta-amino acids is present in pig small intestine.
Collapse
Affiliation(s)
- L K Munck
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark
| | | | | |
Collapse
|
21
|
Munck LK. Chloride-dependent amino acid transport in the small intestine: occurrence and significance. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1241:195-213. [PMID: 7640296 DOI: 10.1016/0304-4157(95)00005-c] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The unidirectional influx of amino acids, D-glucose and ions across the brush-border membrane of the small intestine of different species has been measured in vitro with emphasis on characterization of topographic and species differences and on chloride dependence. The regional differences in transport along the small intestine are outlined and shown to be caused by variation in transport capacity, while the apparent affinity constants are unchanged. Rabbit small intestine is unique by exhibiting maximal rates of transport in the distal ileum and a very steep decline in the oral direction from where tissues are normally harvested for preparation of brush-border membrane vesicles. Transport in the guinea pig and rat is much more constant throughout the small intestine. Since the capacity of nutrient carriers is regulated by their substrates it is possible that bacterial breakdown of peptides and proteins in rabbit distal ileum increases the concentration of amino acids leading to an upregulation of the carriers. Chloride dependence is a characteristics of the carrier rather than the transported amino acid, and is used to improve the classification of amino acid carriers in rabbit small intestine. In this species the imino acid carrier, the beta-amino acid carrier, and the beta-alanine carrier, which should be renamed the B0,+ carrier, are chloride-dependent. The steady-state mucosal uptake of classical substrates for these carriers in biopsies from the human duodenum is also chloride-dependent. The carrier of beta-amino acids emerges as ubiquitous and chloride-dependent, and evidence of cotransport with both sodium and chloride is reviewed. A sodium:chloride:2-methyl-aminoisobutyric acid coupling stoichiometry of approx. 2:1:1 is suggested by ion activation studies. Direct measurements of coupled ion fluxes in rabbit distal ileum confirm that sodium, chloride and 2-methyl-aminoisobutyric acid are cotransported on the imino acid carrier with an identical influx stoichiometry. Control experiments and reference to the literature on the electrophysiology of the small intestine exclude alterations of the membrane potential as a feasible explanation of the chloride dependence. Thus, it is concluded that chloride is cotransported with both sodium and 2-methyl-aminoisobutyric acid across the brush-border membrane of rabbit distal ileum.
Collapse
Affiliation(s)
- L K Munck
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark
| |
Collapse
|