Water Transport Activity of the Plasma Membrane Aquaporin PM28A Is Regulated by Phosphorylation

1998 ◽  
Vol 10 (3) ◽  
pp. 451 ◽  
Author(s):  
Ingela Johansson ◽  
Maria Karlsson ◽  
Vipula K. Shukla ◽  
Maarten J. Chrispeels ◽  
Christer Larsson ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Water Transport ◽  
Transport Activity

Aquaporins in the plasma membrane of leaf callus protoplasts of Actinidia deliciosa var. deliciosa cv. Hayward

2000 ◽  
Vol 27 (1) ◽  
pp. 71
Author(s):  
Quan-Sheng Qiu ◽  
Ze-Zhou Wang ◽  
Nang Zhang ◽  
Qi-Gui Cai ◽  
Rong-Xi Jiang
Keyword(s):  
Plasma Membrane ◽  
Water Transport ◽  
Imaging System ◽  
Inhibitory Effect ◽  
Actinidia Deliciosa ◽  
Transport Activity ◽  
Water Permeability Coefficient ◽  
Osmotic Water ◽  
A Cell ◽  
Protoplast Volume

The water transport activity of Actinidia deliciosa protoplasts was determined using a cell imaging system. Results showed that the protoplast volume increased swiftly when placed in a hypoton-ic medium, and also increased with an increase in medium osmotic gradients. The osmotic water permeability coefficient (Pf) values were 0.118 × 10–3, 0.121 × 10–3, and 0.133 × 10–3 cm s–1 when the osmotic gradients were 75, 100, and 125 mosmol, respectively. The water transport activity of protoplas-ts could be inhibited by HgCl2 and stimulated by amphotericin B. Moreover, ZnCl2 and ZnSO4 had a significant inhibitory effect on the water transport activity of the protoplasts. Our results indicate that the Actinidia deliciosa protoplasts had properties typical of aquaporins, suggesting that aquaporins were present at the plasma membrane.

Mechanisms activating latent functions of PIP aquaporin water channels via the interaction between PIP1 and PIP2 proteins

2020 ◽  
Author(s):  
Mineo Shibasaka ◽  
Tomoaki Horie ◽  
Maki Katsuhara
Keyword(s):  
Plasma Membrane ◽  
Water Transport ◽  
Molecular Mechanisms ◽  
Water Channel ◽  
Amino Acid Replacement ◽  
Middle Part ◽  
Single Amino Acid ◽  
Xenopus Laevis Oocytes ◽  
Transport Activity ◽  
Membrane Type

Abstract Plant plasma-membrane type PIP aquaporins are classified into two groups, PIP1s and PIP2s. In this study, we focused on HvPIP1; 2, a PIP1 in barley (Hordeum vulgare), to dissect the molecular mechanisms that evoke HvPIP1-mediated water transport. No HvPIP1; 2 protein was localized to the plasma membrane when expressed alone in Xenopus laevis oocytes. In contrast, a chimeric HvPIP1; 2 protein (HvPIP1; 2_24NC), in which the N- and C-terminal regions were replaced with the corresponding regions from HvPIP2; 4, was found to localize to the plasma membrane of oocytes. However, HvPIP1; 2_24NC showed no water transport activity in swelling assays. These results suggested that the terminal regions of PIP2 proteins direct PIP proteins to the plasma-membrane, but the re-localization of PIP1 proteins was not sufficient to PIP1s functionality as water channel in a membrane. A single amino acid replacement of threonine by methionine in HvPIP2; 4 (HvPIP2; 4T229M) abolished water transport activity. Co-expression of HvPIP1; 2_24NC either with HvPIP2; 4_12NC or HvPIP2; 4TM_12NC, in which the N- and C-terminal regions were replaced with the corresponding regions of HvPIP1; 2, increased the water transport activity in oocytes. These data provided evidence that the HvPIP1; 2 molecule has own water transport activity and an interaction with the middle part of the HvPIP2; 4 protein (except for the N- and C- termini) is required for HvPIP1; 2 functionality as water channel. This molecular mechanism could be applied to other PIP1s and PIP2s in addition to the known mechanism that the terminal regions of some PIP2s lead some PIP1s to the plasma membrane.

scholarly journals Water Transport Activity of the Plasma Membrane Aquaporin PM28A Is Regulated by Phosphorylation

1998 ◽  
Vol 10 (3) ◽  
pp. 451-459 ◽  
Author(s):  
Ingela Johansson ◽  
Maria Karlsson ◽  
Vipula K. Shukla ◽  
Maarten J. Chrispeels ◽  
Christer Larsson ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Water Transport ◽  
Transport Activity

scholarly journals Expression of solute carrier 7A4 (SLC7A4) in the plasma membrane is not sufficient to mediate amino acid transport activity

2002 ◽  
Vol 364 (3) ◽  
pp. 767-775 ◽  
Author(s):  
Sabine WOLF ◽  
Annette JANZEN ◽  
Nicole VÉKONY ◽  
Ursula MARTINÉ ◽  
Dennis STRAND ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Amino Acid ◽  
Protein Expression ◽  
Amino Acid Transport ◽  
Fluorescent Protein ◽  
Xenopus Laevis Oocytes ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Transport Activity ◽  
Solute Carrier

Member 4 of human solute carrier family 7 (SLC7A4) exhibits significant sequence homology with the SLC7 subfamily of human cationic amino acid transporters (hCATs) [Sperandeo, Borsani, Incerti, Zollo, Rossi, Zuffardi, Castaldo, Taglialatela, Andria and Sebastio (1998) Genomics 49, 230–236]. It is therefore often referred to as hCAT-4 even though no convincing transport activity has been shown for this protein. We expressed SLC7A4 in Xenopus laevis oocytes, but could not detect any transport activity for cationic, neutral or anionic amino acids or for the polyamine putrescine. In addition, human glioblastoma cells stably overexpressing a fusion protein between SLC7A4 and the enhanced green fluorescent protein (EGFP) did not exhibit an increased transport activity for l-arginine. The lack of transport activity was not due to a lack of SLC7A4 protein expression in the plasma membrane, as in both cell types SLC7A4-EGFP exhibited a similar subcellular localization and level of protein expression as functional hCAT-EGFP proteins. The expression of SLC7A4 can be induced in NT2 teratocarcinoma cells by treatment with retinoic acid. However, also for this endogenously expressed SLC7A4, we could not detect any transport activity for l-arginine. Our data demonstrate that the expression of SLC7A4 in the plasma membrane is not sufficient to induce an amino acid transport activity in X. laevis oocytes or human cells. Therefore, SLC7A4 is either not an amino acid transporter or it needs additional (protein) factor(s) to be functional.

scholarly journals N-glycosylation critically regulates function of oxalate transporter SLC26A6

2016 ◽  
Vol 311 (6) ◽  
pp. C866-C873 ◽  
Author(s):  
R. Brent Thomson ◽  
Claire L. Thomson ◽  
Peter S. Aronson
Keyword(s):  
Plasma Membrane ◽  
Intestinal Secretion ◽  
Integral Membrane Proteins ◽  
Extracellular Loop ◽  
Transport Activity ◽  
Intact Cells ◽  
Functional Studies ◽  
And Function ◽  
Oxalate Transport

The brush border Cl−-oxalate exchanger SLC26A6 plays an essential role in mediating intestinal secretion of oxalate and is crucial for the maintenance of oxalate homeostasis and the prevention of hyperoxaluria and calcium oxalate nephrolithiasis. Previous in vitro studies have suggested that SLC26A6 is heavily N-glycosylated. N-linked glycosylation is known to critically affect folding, trafficking, and function in a wide variety of integral membrane proteins and could therefore potentially have a critical impact on SLC26A6 function and subsequent oxalate homeostasis. Through a series of enzymatic deglycosylation studies we confirmed that endogenously expressed mouse and human SLC26A6 are indeed glycosylated, that the oligosaccharides are principally attached via N-glycosidic linkage, and that there are tissue-specific differences in glycosylation. In vitro cell culture experiments were then used to elucidate the functional significance of the addition of the carbohydrate moieties. Biotinylation studies of SLC26A6 glycosylation mutants indicated that glycosylation is not essential for cell surface delivery of SLC26A6 but suggested that it may affect the efficacy with which it is trafficked and maintained in the plasma membrane. Functional studies of transfected SLC26A6 demonstrated that glycosylation at two sites in the putative second extracellular loop of SLC26A6 is critically important for chloride-dependent oxalate transport and that enzymatic deglycosylation of SLC26A6 expressed on the plasma membrane of intact cells strongly reduced oxalate transport activity. Taken together, these studies indicated that oxalate transport function of SLC26A6 is critically dependent on glycosylation and that exoglycosidase-mediated deglycosylation of SLC26A6 has the capacity to profoundly modulate SLC26A6 function.

Exercise training increases the number of glucose transporters in rat adipose cells

1989 ◽  
Vol 257 (4) ◽  
pp. E520-E530
Author(s):  
M. F. Hirshman ◽  
L. J. Wardzala ◽  
L. J. Goodyear ◽  
S. P. Fuller ◽  
E. D. Horton ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Glucose Transport ◽  
Glucose Transporters ◽  
Membrane Transporters ◽  
Control Group ◽  
Transport Activity ◽  
Insulin Stimulation ◽  
Adipose Cell ◽  
Adipose Cell Size ◽  
Adipose Cells

We studied the mechanism for the increase in glucose transport activity that occurs in adipose cells of exercise-trained rats. Glucose transport activity, glucose metabolism, and the subcellular distribution of glucose transporters were measured in adipose cells from rats raised in wheel cages for 6 wk (mean total exercise 350 km/rat), age-matched sedentary controls, and young sedentary controls matched for adipose cell size. Basal rates of glucose transport and metabolism were greater in cells from exercise-trained rats compared with young controls, and insulin-stimulated rates were greater in the exercise-trained rats compared with both age-matched and young controls. The numbers of plasma membrane glucose transporters were not different among groups in the basal state; however, with insulin stimulation, cells from exercise-trained animals had significantly more plasma membrane transporters than young controls or age-matched controls. Exercise-trained rats also had more low-density microsomal transporters than control rats in the basal state. When the total number of glucose transporters/cell was calculated, the exercise-trained rats had 42% more transporters than did either control group. These studies demonstrate that the increased glucose transport and metabolism observed in insulin-stimulated adipose cells from exercise-trained rats is due, primarily, to an increase in the number of plasma membrane glucose transporters translocated from an enlarged intracellular pool.

Topological assessment of oatp1a1: a 12-transmembrane domain integral membrane protein with three N-linked carbohydrate chains

2008 ◽  
Vol 294 (4) ◽  
pp. G1052-G1059 ◽  
Author(s):  
Pijun Wang ◽  
Soichiro Hata ◽  
Yansen Xiao ◽  
John W. Murray ◽  
Allan W. Wolkoff
Keyword(s):  
Plasma Membrane ◽  
Transmembrane Domain ◽  
Organic Anion ◽  
Rat Hepatocytes ◽  
Integral Membrane Protein ◽  
Glycosylation Site ◽  
Domain Model ◽  
Cell Surface Expression ◽  
Transport Activity ◽  
Glycosylation Sites

Organic anion transport protein 1a1 (oatp1a1), a prototypical member of the oatp family of highly homologous transport proteins, is expressed on the basolateral (sinusoidal) surface of rat hepatocytes. The organization of oatp1a1 within the plasma membrane has not been well defined, and computer-based models have predicted possible 12- as well as 10-transmembrane domain structures. Which of oatp1a1's four potential N-linked glycosylation sites are actually glycosylated and their influence on transport function have not been investigated in a mammalian system. In the present study, topology of oatp1a1 in the rat hepatocyte plasma membrane was examined by immunofluorescence analysis using an epitope-specific antibody designed to differentiate a 10- from a 12-transmembrane domain model. To map glycosylation sites, the asparagines at the each of the four N-linked glycosylation consensus sites were mutagenized to glutamines. Mutagenized oatp1a1 constructs were expressed in HeLa cells, and effects on protein expression and transport activity were assessed. These studies revealed that oatp1a1 is a 12-transmembrane-domain protein in which the second and fifth extracellular loops are glycosylated at asparagines 124, 135, and 492, whereas the potential glycosylation site at asparagine 62 is not utilized, consistent with its position in a transmembrane domain. Constructs in which more than one glycosylation site were eliminated had reduced transport activity but not necessarily reduced transporter expression. This was in accord with the finding that fully unglycosylated oatp1a1 was well expressed but located intracellularly with limited transport ability as a consequence of its reduced cell surface expression.

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