An update on renal peptide transporters

2003 ◽  
Vol 284 (5) ◽  
pp. F885-F892 ◽  
Author(s):  
Hannelore Daniel ◽  
Isabel Rubio-Aliaga
Keyword(s):  
Protein Structures ◽  
High Capacity ◽  
Surface Expression ◽  
Transport Processes ◽  
Peptide Transport ◽  
Renal Tubules ◽  
Molecular Physiology ◽  
Peptide Transporters ◽  
Proton Movement ◽  
Transmembrane Potential Difference

The brush-border membrane of renal epithelial cells contains PEPT1 and PEPT2 proteins that are rheogenic carriers for short-chain peptides. The carrier proteins display a distinct surface expression pattern along the proximal tubule, suggesting that initially di- and tripeptides, either filtered or released by surface-bound hydrolases from larger oligopeptides, are taken up by the low-affinity but high-capacity PEPT1 transporter and then by PEPT2, which possesses a higher affinity but lower transport capacity. Both carriers transport essentially all possible di- and tripeptides and numerous structurally related drugs. A unique feature of the mammalian peptide transporters is the capability of proton-dependent electrogenic cotransport of all substrates, regardless of their charge, that is achieved by variable coupling in proton movement along with the substrate down the transmembrane potential difference. This review focuses on the postcloning research efforts to understand the molecular physiology of peptide transport processes in renal tubules and summarizes available data on the underlying genes, protein structures, and transporter function as derived from studies in heterologous expression systems.

Retargeting of the mitochondrial protein p32/gC1Qr to a cytoplasmic compartment and the cell surface

2001 ◽  
Vol 114 (11) ◽  
pp. 2115-2123
Author(s):  
Hans C. van Leeuwen ◽  
Peter O’Hare
Keyword(s):  
Cell Surface ◽  
Protein Interactions ◽  
Mitochondrial Protein ◽  
Physiological Role ◽  
Surface Expression ◽  
Transport Processes ◽  
Cell Surface Expression ◽  
Bacterial Proteins ◽  
Er Chaperone ◽  
Cellular Compartments

p32/gC1qR is a small acidic protein that has been reported to have a broad range of distinct functions and to associate with a wide array of cellular, viral and bacterial proteins. It has been found in each of the main cellular compartments including mitochondria, nucleus and cytoplasm and is also thought to be located at the plasma membrane and secreted into the extracellular matrix. The true physiological role(s) of p32 remains controversial because it has been difficult to reconcile all of the findings on protein interactions and the seemingly disparate observations on compartmentalisation. However, it has been proposed that p32 is somehow involved in transport processes connecting diverse cellular compartments and the cell surface. Here we show that native p32 appears to be localised mainly in the mitochondria and is not detectable on the cell surface. However, addition of a short tag to the N-terminus of p32 appears to block its mitochondrial targeting, resulting in redirection into a cytoplasmic vesicular pattern, overlapping with the endoplasmic reticulum. The redirection of p32 results in an alteration in and co-localisation with ER markers including calreticulin, a lumenal ER chaperone. Furthermore, we show both by immunofluorescence and cross-linking studies that this also results in cell-surface expression of p32. These results indicate that, at least under certain circumstances, p32 can be retargeted and may help to provide an explanation for the diverse observations on its localization.

scholarly journals Modulation of Transporter Associated with Antigen Processing (TAP)-Mediated Peptide Import into the Endoplasmic Reticulum by Flavivirus Infection

2001 ◽  
Vol 75 (12) ◽  
pp. 5663-5671 ◽  
Author(s):  
Frank Momburg ◽  
Arno Müllbacher ◽  
Mario Lobigs
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Mhc Class I ◽  
Antigen Processing ◽  
Surface Expression ◽  
Class I ◽  
Peptide Transport ◽  
Cell Surface Expression ◽  
Flavivirus Infection ◽  
Mhc Class I Molecules

ABSTRACT In contrast to many other viruses that escape the cellular immune response by downregulating major histocompatibility complex (MHC) class I molecules, flavivirus infection can upregulate their cell surface expression. Previously we have presented evidence that during flavivirus infection, peptide supply to the endoplasmic reticulum is increased (A. Müllbacher and M. Lobigs, Immunity 3:207–214, 1995). Here we show that during the early phase of infection with different flaviviruses, the transport activity of the peptide transporter associated with antigen processing (TAP) is augmented by up to 50%. TAP expression is unaltered during infection, and viral but not host macromolecular synthesis is required for enhanced peptide transport. This study is the first demonstration of transient enhancement of TAP-dependent peptide import into the lumen of the endoplasmic reticulum as a consequence of a viral infection. We suggest that the increased supply of peptides for assembly with MHC class I molecules in flavivirus-infected cells accounts for the upregulation of MHC class I cell surface expression with the biological consequence of viral evasion of natural killer cell recognition.

Mechanism of leptin removal from the circulation by the kidney

1997 ◽  
Vol 155 (3) ◽  
pp. 577-585 ◽  
Author(s):  
F Cumin ◽  
HP Baum ◽  
N Levens
Keyword(s):  
Glomerular Filtration ◽  
Renal Plasma Flow ◽  
High Capacity ◽  
Renal Tubules ◽  
Primary Role ◽  
Sprague Dawley ◽  
Arterial Blood ◽  
Wide Range ◽  
Metabolic Degradation ◽  
Plasma Leptin

This study was performed to test the hypothesis that the kidneys play a primary role in the clearance of endogenous leptin from the circulation. Lean male Sprague-Dawley rats were anesthetized and subjected to various surgical manipulations of the kidneys. Sixty minutes after surgery arterial blood samples were taken at 1-h intervals for up to 8 h. Plasma leptin levels were determined by radioimmunoassay. Bilateral nephrectomy induced a rapid increase in plasma leptin concentrations above control values, indicating that the kidneys are important for the elimination of leptin from the circulation. Leptin was not metabolized across the renal circulation and was extracted intact by the kidney. Simultaneous measurement of renal plasma flow established renal leptin extraction at approximately 6.5 ng/min for both kidneys. Compared with the quantities extracted from the plasma, leptin was only present in the urine in small quantities, indicating extensive metabolic degradation in the renal tubules. High plasma leptin levels were not maintained after binephrectomy indicating that pathways other than the kidneys are also responsible for leptin clearance. Seven hours after bilateral ureteral ligation, a procedure which lowers glomerular filtration, plasma leptin levels were slightly elevated. The renal extraction of leptin did not change over a wide range of plasma leptin concentrations suggesting that renal leptin extraction is a high capacity, non-saturable process most probably glomerular filtration. Endogenous leptin is rapidly cleared from the circulation by glomerular filtration followed by metabolic degradation in the renal tubules.

Cellular and molecular mechanisms of renal peptide transport

1997 ◽  
Vol 273 (1) ◽  
pp. F1-F8 ◽  
Author(s):  
H. Daniel ◽  
M. Herget
Keyword(s):  
Amino Acid ◽  
Epithelial Cells ◽  
Molecular Mechanisms ◽  
Functional Expression ◽  
Model Systems ◽  
Peptide Transport ◽  
Molecular Architecture ◽  
Renal Handling ◽  
Peptide Transporters ◽  
Transporter Family

Renal epithelial cells express membrane transport proteins capable of cellular uptake of a large variety of di- and tripeptides. These transporters contribute to renal amino acid homeostasis and the efficiency of conservation of amino acid nitrogen. In addition, these transporters appear to play a role in the renal handling of xenobiotics that possess a peptide backbone. Peptide carriers specialized in transport of di- and tripeptides have been identified in bacteria, fungi, plants, and epithelial cells of mammalian intestine and kidney. They appear to represent an archaic transporter family conserved throughout evolution. As a unique feature, these peptide carriers utilize a transmembrane-electrochemical proton gradient as the driving force that enables them to transport peptides against a concentration gradient. Renal peptide transporters have been characterized in terms of mechanism of transport function and substrate specificity in a number of model systems. Within the last two years, kidney peptide transporters of a variety of species have been identified by cloning techniques. In this review we discuss the physiological importance of renal peptide carriers and the transport mechanisms at the cellular level. We also present the recent advancements in functional expression of the cloned proteins that provide first insights into their molecular architecture and mode of operation.

Molecular physiology of norepinephrine and serotonin transporters.

1994 ◽  
Vol 196 (1) ◽  
pp. 263-281 ◽  
Author(s):  
R D Blakely ◽  
L J De Felice ◽  
H C Hartzell
Keyword(s):  
Surface Expression ◽  
Electrophysiological Recording ◽  
Molecular Physiology ◽  
Serotonin Transporters ◽  
Hek 293 ◽  
293 Cells ◽  
Biophysical Analysis ◽  
Nutrients Availability ◽  
Heterologous Expression Systems ◽  
Definition Of

Cocaine- and antidepressant-sensitive norepinephrine and serotonin transporters (NETs and SERTs) are closely related members of the Na+/Cl- transporter gene family, whose other members include transporters for inhibitory amino acid transmitters, neuromodulators, osmolytes and nutrients. Availability of cloned NET and SERT cDNAs has permitted rapid progress in the definition of cellular sites of gene expression, the generation of transporter-specific antibodies suitable for biosynthetic and localization studies, the examination of structure-function relationships in heterologous expression systems and a biophysical analysis of transporter function. In situ hybridization and immunocytochemical studies indicate a primary expression of NET and SERT genes in brain by noradrenergic and serotonergic neurons, respectively. Both NET and SERT are synthesized as glycoproteins, with multiple glycosylation states apparent for SERT proteins in the brain and periphery. N-glycosylation of NET and SERT appears to be essential for transporter assembly and surface expression, but not for antagonist binding affinity. Homology cloning efforts have revealed novel NET and SERT homologs in nonmammalian species that are of potential value in the delineation of the precise sites for substrate and antagonist recognition, including a Drosophila melanogaster SERT with NET-like pharmacology. Electrophysiological recording of human NETs and SERTs stably expressed in HEK-293 cells reveals that both transporters move charge across the plasma membrane following the addition of substrates; these currents can be blocked by NET-and SERT-selective antagonists as well as by cocaine.

Transport and metabolism of L-glutamate during oxygenation, anoxia, and reoxygenation of rat cardiac myocytes

1996 ◽  
Vol 270 (5) ◽  
pp. H1825-H1832 ◽  
Author(s):  
L. M. Dinkelborg ◽  
R. K. Kinne ◽  
M. K. Grieshaber
Keyword(s):  
Amino Acid ◽  
Glutamate Uptake ◽  
High Capacity ◽  
Competitive Inhibitor ◽  
Transport Processes ◽  
Heart Cells ◽  
Adult Rat ◽  
High Affinity ◽  
Glutamate Concentration ◽  
Rat Heart Cells

The intracellular glutamate concentration of oxygenated, isolated adult rat heart cells incubated with 0.15 mM glutamate amounts to 2.89 +/- 0.6 mM. Under these conditions the velocity of glutamate transport was 24.3 +/- 1.6 pmol.min-1.mg protein-1 and occurs via a high-affinity carrier characterized by an apparent affinity (K(m)) value of 0.18 +/- 0.03 mM. At high glutamate concentrations ( > 1mM) this high-affinity transport system is superimposed by additional uptake processes of a low affinity but a high capacity for glutamate. The 1.6-fold increased uptake of glutamate observed during 30 min of anoxic incubation of cardiomyocytes does not prevent an intracellular decrease in this amino acid to a concentration of 0.49 mM. After 15 min reoxygenation of cardiomyocytes the intracellular glutamate content increases to the control values of oxygenated cells. Only 2.4% of the glutamate increase after reoxygenation is due to the transport o glutamate from the incubation medium. The competitive inhibitor of transaminases, aminooxyacetate, prevents both the observed intracellular decrease in glutamate during anoxia and the increase in intracellular glutamate after reoxygenation of cardiomyocytes. Half of the amino groups needed for the synthesis of glutamate originate from intracellular alanine, which increases during anoxia and is metabolized during reoxygenation of cardiomyocytes. The velocity of the glutamate uptake of cardiomyocytes incubated in a medium containing 10 mM L-glutamate amounted to 728 +/- 140 pmol.min-1.mg protein-1. During anoxic incubation of cardiomyocytes at this high extracellular glutamate concentration, the intracellular glutamate breakdown may be compensated by a simultaneous uptake of this amino acid via the transport processes characterized by a high capacity

scholarly journals The peptide transport system Opt is involved in both nutrition and environmental sensing during growth of Lactococcus lactis in milk

Microbiology ◽  
2011 ◽  
Vol 157 (6) ◽  
pp. 1612-1619 ◽  
Author(s):  
Mauld Lamarque ◽  
Dominique Aubel ◽  
Jean-Christophe Piard ◽  
Christophe Gilbert ◽  
Vincent Juillard ◽  
...  
Keyword(s):  
Lactococcus Lactis ◽  
Transport System ◽  
Binding Proteins ◽  
Peptide Binding ◽  
Peptide Transport ◽  
Dual Function ◽  
Peptide Transporters ◽  
Transport Mutants ◽  
Dependent Transport ◽  
Distinct Peptide

Lactococcus lactis is known to take up extracellular peptides via at least three distinct peptide transporters. The well-described oligopeptide transporter Opp alone is able to ensure the growth of L. lactis in milk, while the di- and tripeptide transporter DtpT is involved in a peptide-dependent signalling mechanism. The oligopeptide Opt transporter displays two peptide-binding proteins, OptA and OptS. We previously demonstrated that OptA-dependent transport is dedicated to nutritional peptides, as an optABCDF mutant (of a strain devoid of Opp) has an impaired capacity to grow in milk. Using isogenic peptide transport mutants, this study shows that biosynthesis of the Opt transporter is much less sensitive to downregulation that is dependent on extracellular peptides taken up by DtpT than is Opp biosynthesis; this peptide-dependent regulation relies on the transcriptional repressor CodY. We demonstrate the dual function of the Opt system; while OptA contributes to the bacterial nutrition during growth in milk, OptS is involved in the transport of signalling peptides derived from milk and controlling opp expression. So, these results shed new light on the peptide-dependent regulation relying on two peptide transporters with different specificities: DtpT and Opt (via OptS).

Characterization of tetraethylammonium uptake across the basolateral membrane of the Drosophila Malpighian (renal) tubule

2005 ◽  
Vol 289 (2) ◽  
pp. R495-R504 ◽  
Author(s):  
Mark R. Rheault ◽  
Donna M. Debicki ◽  
Michael J. O'Donnell
Keyword(s):  
Organic Cation ◽  
Basolateral Membrane ◽  
Transport Processes ◽  
Malpighian Tubules ◽  
Type I ◽  
Renal Tubules ◽  
Maximal Rate ◽  
High K ◽  
Total Transport ◽  
Low K

Basolateral transport of the prototypical type I organic cation tetraethylammonium (TEA) by the Malpighian tubules of Drosophila melanogaster was studied using measurements of basolateral membrane potential (Vbl) and uptake of [14C]-labeled TEA. TEA uptake was metabolically dependent and saturable (maximal rate of mediated TEA uptake by all potential transport processes, reflecting the total transport capacity of the membrane, 0.87 pmol·tubule−1·min−1; concentration of TEA at 0.5 of the maximal rate of TEA uptake value, 24 μM). TEA uptake in Malpighian tubules was inhibited by a number of type I (e.g., cimetidine, quinine, and TEA) and type II (e.g., verapamil) organic cations and was dependent on Vbl. TEA uptake was reduced in response to conditions that depolarized Vbl (high-K+ saline, Na+-free saline, NaCN) and increased in conditions that hyperpolarized Vbl (low-K+ saline). Addition of TEA to the saline bathing Malpighian tubules rapidly depolarized the Vbl, indicating that TEA uptake was electrogenic. Blockade of K+ channels with Ba2+ did not block effects of TEA on Vbl or TEA uptake indicating that TEA uptake does not occur through K+ channels. This is the first study to provide physiological evidence for an electrogenic carrier-mediated basolateral organic cation transport mechanism in insect Malpighian tubules. Our results also suggest that the mechanism of basolateral TEA uptake by Malpighian tubules is distinct from that found in vertebrate renal tubules.

scholarly journals Determinants of cation transport selectivity: Equilibrium binding and transport kinetics

2015 ◽  
Vol 146 (1) ◽  
pp. 3-13 ◽  
Author(s):  
Steve W. Lockless
Keyword(s):  
Binding Sites ◽  
Protein Structures ◽  
Cation Transport ◽  
Transport Processes ◽  
Ion Binding ◽  
Nonselective Cation Channels ◽  
Equilibrium Binding ◽  
Ion Binding Sites ◽  
Primary Focus ◽  
The Relationship

The crystal structures of channels and transporters reveal the chemical nature of ion-binding sites and, thereby, constrain mechanistic models for their transport processes. However, these structures, in and of themselves, do not reveal equilibrium selectivity or transport preferences, which can be discerned only from various functional assays. In this Review, I explore the relationship between cation transport protein structures, equilibrium binding measurements, and ion transport selectivity. The primary focus is on K+-selective channels and nonselective cation channels because they have been extensively studied both functionally and structurally, but the principles discussed are relevant to other transport proteins and molecules.

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