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Involvement of sialic acid in the regulation of γ--aminobutyric acid uptake activity of γ-aminobutyric acid transporter 1.
- Source :
-
Glycobiology [Glycobiology] 2011 Mar; Vol. 21 (3), pp. 329-39. Date of Electronic Publication: 2010 Nov 02. - Publication Year :
- 2011
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Abstract
- The γ-aminobutyric acid (GABA) transporters (GATs) have long been recognized for their key role in the uptake of neurotransmitters. The GAT1 belongs to the family of Na(+)- and Cl(-)-coupled transport proteins, which possess 12 putative transmembrane (TM) domains and three N-glycosylation sites on the extracellular loop between TM domains 3 and 4. Previously, we demonstrated that terminal trimming of N-glycans is important for the GABA uptake activity of GAT1. In this work, we examined the effect of deficiency, removal or oxidation of surface sialic acid residues on GABA uptake activity to investigate their role in the GABA uptake of GAT1. We found that the reduced concentration of sialic acid on N-glycans was paralleled by a decreased GABA uptake activity of GAT1 in Chinese hamster ovary (CHO) Lec3 cells (mutant defective in sialic acid biosynthesis) in comparison to CHO cells. Likewise, either enzymatic removal or chemical oxidation of terminal sialic acids using sialidase or sodium periodate, respectively, resulted in a strong reduction in GAT1 activity. Kinetic analysis revealed that deficiency, removal or oxidation of terminal sialic acids did not affect the K(m) GABA values. However, deficiency and removal of terminal sialic acids of GAT1 reduced the V(max) GABA values with a reduced apparent affinity for extracellular Na(+). Oxidation of cell surface sialic acids also strongly reduced V(max) without affecting both affinities of GAT1 for GABA and Na(+), respectively. These results demonstrated for the first time that the terminal sialic acid of N-linked oligosaccharides of GAT1 plays a crucial role in the GABA transport process.
- Subjects :
- Animals
CHO Cells
Cricetinae
Cricetulus
GABA Plasma Membrane Transport Proteins biosynthesis
GABA Plasma Membrane Transport Proteins chemistry
GABA Uptake Inhibitors pharmacology
Green Fluorescent Proteins biosynthesis
Green Fluorescent Proteins chemistry
HEK293 Cells
Humans
Kinetics
N-Acetylneuraminic Acid chemistry
Neuraminidase pharmacology
Oxidation-Reduction
Periodic Acid pharmacology
Protein Binding
Protein Transport
Recombinant Fusion Proteins biosynthesis
Recombinant Fusion Proteins chemistry
GABA Plasma Membrane Transport Proteins metabolism
Green Fluorescent Proteins metabolism
N-Acetylneuraminic Acid metabolism
Recombinant Fusion Proteins metabolism
Sodium metabolism
gamma-Aminobutyric Acid metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 1460-2423
- Volume :
- 21
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Glycobiology
- Publication Type :
- Academic Journal
- Accession number :
- 21045010
- Full Text :
- https://doi.org/10.1093/glycob/cwq166