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Bröer S, Bröer A, Hansen JT, Bubb WA, Balcar VJ, Nasrallah FA, Garner B, Rae C. Alanine metabolism, transport, and cycling in the brain. J Neurochem 2007; 102:1758-1770. [PMID: 17504263 DOI: 10.1111/j.1471-4159.2007.04654.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Brain glutamate/glutamine cycling is incomplete without return of ammonia to glial cells. Previous studies suggest that alanine is an important carrier for ammonia transfer. In this study, we investigated alanine transport and metabolism in Guinea pig brain cortical tissue slices and prisms, in primary cultures of neurons and astrocytes, and in synaptosomes. Alanine uptake into astrocytes was largely mediated by system L isoform LAT2, whereas alanine uptake into neurons was mediated by Na(+)-dependent transporters with properties similar to system B(0) isoform B(0)AT2. To investigate the role of alanine transport in metabolism, its uptake was inhibited in cortical tissue slices under depolarizing conditions using the system L transport inhibitors 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid and cycloleucine (1-aminocyclopentanecarboxylic acid; cLeu). The results indicated that alanine cycling occurs subsequent to glutamate/glutamine cycling and that a significant proportion of cycling occurs via amino acid transport system L. Our results show that system L isoform LAT2 is critical for alanine uptake into astrocytes. However, alanine does not provide any significant carbon for energy or neurotransmitter metabolism under the conditions studied.
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Affiliation(s)
- Stefan Bröer
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
| | - Angelika Bröer
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
| | - Jonas T Hansen
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
| | - William A Bubb
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
| | - Vladimir J Balcar
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
| | - Fatima A Nasrallah
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
| | - Brett Garner
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
| | - Caroline Rae
- School of Biochemistry and Molecular Biology, Australian National University, Acton, Canberra ACT, AustraliaSchool of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, AustraliaDepartment of Anatomy and Histology, The University of Sydney, Sydney, New South Wales, AustraliaPrince of Wales Medical Research Institute, Randwick, New South Wales, AustraliaSchool of Chemistry, The University of New South Wales, Sydney, New South Wales, Australia
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Everberg H, Clough J, Henderson P, Jergil B, Tjerneld F, Ramírez IBR. Isolation of Escherichia coli inner membranes by metal affinity two-phase partitioning. J Chromatogr A 2006; 1118:244-52. [PMID: 16647072 DOI: 10.1016/j.chroma.2006.03.123] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2006] [Revised: 03/29/2006] [Accepted: 03/31/2006] [Indexed: 10/24/2022]
Abstract
As reduction of sample complexity is a central issue in membrane proteomic research, the need for new pre-fractionation methods is significant. Here we present a method for fast and efficient enrichment of Escherichia coli inner membranes expressing a His-tagged integral membrane L-fucose-proton symporter (FucP). An enriched inner membrane fraction was obtained from a crude membrane mixture using affinity two-phase partitioning in combination with nickel-nitrilotriacetic acid (Ni-NTA) immobilized on agarose beads. Due to interaction between the beads and FucP, inner membranes were selectively partitioned to the bottom phase of a polymer/polymer aqueous two-phase system consisting of poly(ethylene glycol) (PEG) and dextran. The partitioning of membranes was monitored by assaying the activity of an inner membrane marker protein and measuring the total protein content in both phases. The enrichment of inner membrane proteins in the dextran phase was also investigated by proteomic methodology, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), trypsin digestion and liquid chromatography in combination with tandem mass spectrometry (LC-MS/MS). Using a high level of significance (99.95%) in the subsequent database search, 36 proteins assigned to the inner membrane were identified in the bottom phase, compared to 29 when using the standard sucrose gradient centrifugation method for inner membrane isolation. Furthermore, metal affinity two-phase partitioning was up to 10 times faster than sucrose gradient centrifugation. The separation conditions in these model experiments provide a basis for the selective isolation of E. coli membranes expressing His-tagged proteins and can therefore facilitate research on such membrane proteomes.
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Affiliation(s)
- Henrik Everberg
- Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, S-22100 Lund, Sweden
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Bröer A, Tietze N, Kowalczuk S, Chubb S, Munzinger M, Bak L, Bröer S. The orphan transporter v7-3 (slc6a15) is a Na+-dependent neutral amino acid transporter (B0AT2). Biochem J 2006; 393:421-30. [PMID: 16185194 PMCID: PMC1383701 DOI: 10.1042/bj20051273] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2005] [Revised: 08/23/2005] [Accepted: 09/26/2005] [Indexed: 01/11/2023]
Abstract
Transporters of the SLC6 (solute carrier 6) family play an important role in the removal of neurotransmitters in brain tissue and in amino acid transport in epithelial cells. In the present study, we demonstrate that mouse v7-3 (slc6a15) encodes a transporter for neutral amino acids. The transporter is functionally and sequence related to B(0)AT1 (slc6a19) and was hence named B(0)AT2. Leucine, isoleucine, valine, proline and methionine were recognized by the transporter, with values of K(0.5) (half-saturation constant) ranging from 40 to 200 microM. Alanine, glutamine and phenylalanine were low-affinity substrates of the transporter, with K(0.5) values in the millimolar range. Transport of neutral amino acids via B(0)AT2 was Na+-dependent, Cl--independent and electrogenic. Superfusion of mouse B(0)AT2-expressing oocytes with amino acid substrates generated robust inward currents. Na+-activation kinetics of proline transport and uptake under voltage clamp suggested a 1:1 Na+/amino acid co-transport stoichiometry. Susbtrate and co-substrate influenced each other's K(0.5) values, suggesting that they share the same binding site. A mouse B(0)AT2-like transport activity was detected in synaptosomes and cultured neurons. A potential role of B(0)AT2 in transporting neurotransmitter precursors and neuromodulators is proposed.
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Key Words
- amino acid transport
- b0at2
- neurotransmitter transporter family
- proline
- solute carrier 6 (slc6) transporter family
- transport mechanism
- (me)aib, (n-methyl)aminoisobutyric acid
- bch, 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid
- mb0at2, mouse b0at2
- est, expressed sequence tag
- gaba, γ-aminobutyric acid
- hbss, hanks balanced salt solution
- mct1, monocarboxylate transporter 1
- nmdg, n-methyl-d-glucamine
- pat1, proton amino acid transporter 1
- prot, proline transporter
- rt, reverse transcription
- slc6, solute carrier 6
- snat1, system n/a transporter 1
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Affiliation(s)
- Angelika Bröer
- School of Biochemistry & Molecular Biology, Australian National University, Canberra, ACT 0200, Australia
| | - Nadine Tietze
- School of Biochemistry & Molecular Biology, Australian National University, Canberra, ACT 0200, Australia
| | - Sonja Kowalczuk
- School of Biochemistry & Molecular Biology, Australian National University, Canberra, ACT 0200, Australia
| | - Sarah Chubb
- School of Biochemistry & Molecular Biology, Australian National University, Canberra, ACT 0200, Australia
| | - Michael Munzinger
- School of Biochemistry & Molecular Biology, Australian National University, Canberra, ACT 0200, Australia
| | - Lasse K. Bak
- School of Biochemistry & Molecular Biology, Australian National University, Canberra, ACT 0200, Australia
| | - Stefan Bröer
- School of Biochemistry & Molecular Biology, Australian National University, Canberra, ACT 0200, Australia
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Everberg H, Sivars U, Emanuelsson C, Persson C, Englund AK, Haneskog L, Lipniunas P, Jörntén-Karlsson M, Tjerneld F. Protein pre-fractionation in detergent–polymer aqueous two-phase systems for facilitated proteomic studies of membrane proteins. J Chromatogr A 2004; 1029:113-24. [PMID: 15032356 DOI: 10.1016/j.chroma.2003.12.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Pre-fractionation of a complex mixture of proteins increases the resolution in analytical separations of proteins from cells, tissues or organisms. Here we demonstrate a novel method for pre-fractionation of membrane proteins by a detergent-based aqueous two-phase system. Membrane proteins are strongly under-represented in proteomic studies based on two-dimensional electrophoresis (2-DE). As a model system, we have isolated mitochondria from the yeast Saccharomyces cerevisiae. Mitochondrial proteins were fractionated in an aqueous two-phase system consisting of the polymer poly(ethylene glycol) and either of two commonly used non-ionic detergents, Triton X-114 or dodecyl maltoside (DDM). Soluble proteins partitioned mainly to the polymer phase while membrane proteins were enriched in the detergent phase, as identified from one-dimensional electrophoresis (1-DE) and/or 2-DE followed by mass spectrometric analysis. Pre-fractionation was further enhanced by addition of an anionic detergent, sodium dodecyl sulfate, or a chaotropic salt, NaClO4, and by raising the pH in the system. The two-phase system pre-fractionation was furthermore combined with an alternative two-dimensional high-resolution separation method, namely ion-exchange chromatography and 1-DE. By this approach a larger number of membrane proteins could be identified compared to separation with conventional 2-DE. Thus, pre-fractionation of complex protein mixtures using the aqueous two-phase systems developed here will help to disclose larger proportions of membrane proteins in different proteomes.
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Affiliation(s)
- Henrik Everberg
- Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-22100 Lund, Sweden
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Bradley AJ, Murad KL, Regan KL, Scott MD. Biophysical consequences of linker chemistry and polymer size on stealth erythrocytes: size does matter. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1561:147-58. [PMID: 11997115 DOI: 10.1016/s0005-2736(02)00339-5] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Immunocamouflaged red blood cells (RBC) are produced by cell surface derivatization with methoxypolyethylene glycol (mPEG). These immunologically attenuated cells may reduce the risk of allosensitization in chronically transfused patients. To characterize the effects of differing linker chemistries and polymer lengths, RBC were modified with cyanuric chloride activated mPEG (C-mPEG 5 kDa), benzotriazole carbonate methoxyPEG (BTC-mPEG; 5 or 20 kDa) or N-hydroxysuccinimidyl ester of mPEG propionic acid (SPA-mPEG; 2, 5 or 20 kDa). Biophysical methods including particle electrophoresis and aqueous two-phase polymer partitioning were employed to compare the PEG derivatives. While C-mPEG was faster reacting, both BTC-mPEG and SPA-mPEG gave comparable findings after 1 h. Both PEG surface density and molecular mass had a large effect on RBC surface properties. Proportional changes in electrophoretic mobility and preferential phase partitioning were achieved by increasing either the quantity of surface PEG or the PEG molecular mass. In addition, two-phase partitioning may provide a means for efficiently removing unmodified or lightly modified (hence potentially immunogenic) RBC in the clinical setting. Furthermore, mPEG modification significantly inhibits cell-cell interaction as evidenced by loss of Rouleaux formation and, consequently, sedimentation rate. Importantly, BTC-mPEG 20 kDa RBC showed normal in vivo survival in mice at immunoprotective concentrations (up to 2 mM).
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Affiliation(s)
- Amanda J Bradley
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, NY, USA
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