scholarly journals Mutation of leucine-92 selectively reduces the apparent affinity of inosine, guanosine, NBMPR [S6-(4-nitrobenzyl)-mercaptopurine riboside] and dilazep for the human equilibrative nucleoside transporter, hENT1

2004 ◽  
Vol 380 (1) ◽  
pp. 131-137 ◽  
Author(s):  
Christopher J. ENDRES ◽  
Dhruba J. SENGUPTA ◽  
Jashvant D. UNADKAT
Keyword(s):  
Amino Acid ◽  
Yeast Cells ◽  
Nucleoside Transporter ◽  
Wild Type ◽  
Equilibrative Nucleoside Transporter ◽  
Ic50 Values ◽  
Km Value ◽  
Adenosine Transport ◽  
The Media ◽  
First Time

We developed a yeast-based assay for selection of hENT1 (human equilibrative nucleoside transporter 1) mutants that have altered affinity for hENT1 inhibitors and substrates. In this assay, expression of hENT1 in a yeast strain deficient in adenine biosynthesis (ade2) permits yeast growth on a plate lacking adenine but containing adenosine, a hENT1 substrate. This growth was prevented when inhibitors of hENT1 {e.g. NBMPR [S6-(4-nitrobenzyl)-mercaptopurine riboside], dilazep or dipyridamole} were included in the media. To identify hENT1 mutants resistant to inhibition by these compounds, hENT1 was randomly mutagenized and introduced into this strain. Mutation(s) that allowed growth of yeast cells in the presence of these inhibitors were then identified and characterized. Mutants harbouring amino acid changes at Leu92 exhibited resistance to NBMPR and dilazep but not dipyridamole. The IC50 values of NBMPR and dilazep for [3H]adenosine transport by one of these mutants L92Q (Leu92→Gln) were approx. 200- and 4-fold greater when compared with the value for the wild-type hENT1, whereas that for dipyridamole remained unchanged. Additionally, when compared with the wild-type transporter, [3H]adenosine transport by L92Q transporter was significantly resistant to inhibition by inosine and guanosine but not by adenosine or pyrimidines. The Km value for inosine transport was approx. 4-fold greater for the L92Q mutant (260±16 µM) when compared with the wild-type transporter (65±7.8 µM). We have identified for the first time an amino acid residue (Leu92) of hENT1 that, when mutated, selectively alters the affinity of hENT1 to transport the nucleosides inosine and guanosine and its sensitivity to the inhibitors NBMPR and dilazep.

Mutation of Trp29 of human equilibrative nucleoside transporter 1 alters affinity for coronary vasodilator drugs and nucleoside selectivity

2008 ◽  
Vol 414 (2) ◽  
pp. 291-300 ◽  
Author(s):  
Robert J. Paproski ◽  
Frank Visser ◽  
Jing Zhang ◽  
Tracey Tackaberry ◽  
Vijaya Damaraju ◽  
...  
Keyword(s):  
Nucleoside Transport ◽  
Nucleoside Transporter ◽  
Transport Activity ◽  
Sequence Alignments ◽  
Equilibrative Nucleoside Transporter ◽  
Vasodilator Drugs ◽  
Selective Loss ◽  
Coronary Vasodilator ◽  
Ic50 Values ◽  
Adenosine Transport

hENT1 (human equilibrative nucleoside transporter 1) is inhibited by nanomolar concentrations of various structurally distinct coronary vasodilator drugs, including dipyridamole, dilazep, draflazine, soluflazine and NBMPR (nitrobenzylmercaptopurine ribonucleoside). When a library of randomly mutated hENT1 cDNAs was screened using a yeast-based functional complementation assay for resistance to dilazep, a clone containing the W29G mutation was identified. Multiple sequence alignments revealed that this residue was highly conserved. Mutations at Trp29 were generated and tested for adenosine transport activity and inhibitor sensitivity. Trp29 mutations significantly reduced the apparent Vmax and/or increased the apparent Km values for adenosine transport. Trp29 mutations increased the IC50 values for hENT1 inhibition by dipyridamole, dilazep, NBMPR, soluflazine and draflazine. NBMPR and soluflazine displayed remarkably similar trends, with large aromatic substitutions at residue 29 resulting in the lowest IC50 values, suggesting that both drugs could interact via ring-stacking interactions with Trp29. The W29T mutant displayed a selective loss of pyrimidine nucleoside transport activity, which contrasts with the previously identified L442I mutant that displayed a selective loss of purine nucleoside transport. W29T, L442I and the double mutant W29T/L442I were characterized kinetically for nucleoside transport activity. A helical wheel projection of TM (transmembrane segment) 1 suggests that Trp29 is positioned close to Met33, implicated previously in nucleoside and inhibitor recognition, and that both residues line the permeant translocation pathway. The data also suggest that Trp29 forms part of, or lies close to, the binding sites for dipyridamole, dilazep, NBMPR, soluflazine and draflazine.

scholarly journals Amino acids whose intracellular levels change most during aging alter chronological lifespan of fission yeast

2020 ◽  
Author(s):  
Charalampos Rallis ◽  
Michael Mülleder ◽  
Graeme Smith ◽  
Yan Zi Au ◽  
Markus Ralser ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Fission Yeast ◽  
Yeast Cells ◽  
Total Amino Acid ◽  
Wild Type ◽  
Chronological Lifespan ◽  
Biomarkers Of Aging ◽  
Concentration Changes ◽  
Amino Acid Levels

AbstractAmino acid deprivation or supplementation can affect cellular and organismal lifespan, but we know little about the role of concentration changes in free, intracellular amino acids during aging. Here, we determine free amino-acid levels during chronological aging of non-dividing fission yeast cells. We compare wild-type with long-lived mutant cells that lack the Pka1 protein of the protein kinase A signalling pathway. In wild-type cells, total amino-acid levels decrease during aging, but much less so in pka1 mutants. Two amino acids strongly change as a function of age: glutamine decreases, especially in wild-type cells, while aspartate increases, especially in pka1 mutants. Supplementation of glutamine is sufficient to extend the chronological lifespan of wild-type but not of pka1Δ cells. Supplementation of aspartate, on the other hand, shortens the lifespan of pka1Δ but not of wild-type cells. Our results raise the possibility that certain amino acids are biomarkers of aging, and their concentrations during aging can promote or limit cellular lifespan.

Inositol regulates phosphatidylglycerolphosphate synthase expression in Saccharomyces cerevisiae

1988 ◽  
Vol 8 (11) ◽  
pp. 4773-4779
Author(s):  
M L Greenberg ◽  
S Hubbell ◽  
C Lam
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Biosynthetic Enzymes ◽  
Phospholipid Synthesis ◽  
Wild Type ◽  
Mitochondrial Inner Membrane ◽  
Regulatory Circuit ◽  
The Media ◽  
Constitutive Synthesis ◽  
First Time ◽  
Phosphatidylcholine Synthesis

The enzyme phosphatidylglycerolphosphate synthase (PGPS; CDPdiacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase; EC 2.7.8.5) catalyzes the committed step in the synthesis of cardiolipin, a phospholipid found predominantly in the mitochondrial inner membrane. To determine whether PGPS is regulated by cross-pathway control, we analyzed PGPS expression under conditions in which the regulation of general phospholipid synthesis could be examined. The addition of inositol resulted in a three- to fivefold reduction in PGPS expression in wild-type cells in the presence or absence of exogenous choline. The reduction in enzyme activity in response to inositol was seen in minutes, suggesting that inactivation or degradation of the enzyme plays an important role in inositol-mediated repression of PGPS. In cho2 and opi3 mutants, which are blocked in phosphatidylcholine synthesis, inositol-mediated repression of PGPS did not occur unless choline was added to the media. Three previously identified genes that regulate general phospholipid synthesis, INO2, INO4, and OP11, did not affect PGPS expression. Thus, ino2 and ino4 mutants, which are unable to derepress biosynthetic enzymes involved in general phospholipid synthesis, expressed wild-type levels of PGPS activity under derepressing conditions. PGPS expression in the opi1 mutant, which exhibits constitutive synthesis of general phospholipid biosynthetic enzymes, was fully repressed in the presence of inositol and partially repressed even in the absence of inositol. These results demonstrate for the first time that an enzymatic step in cardiolipin synthesis is coordinately controlled with general phospholipid synthesis but that this control is not mediated by the same genetic regulatory circuit.

Identification of Cys140 in helix 4 as an exofacial cysteine residue within the substrate-translocation channel of rat equilibrative nitrobenzylthioinosine (NBMPR)-insensitive nucleoside transporter rENT2

2001 ◽  
Vol 353 (2) ◽  
pp. 387-393 ◽  
Author(s):  
Sylvia Y. M. YAO ◽  
Manickavasagam SUNDARAM ◽  
Eugene G. CHOMEY ◽  
Carol E. CASS ◽  
Stephen A. BALDWIN ◽  
...  
Keyword(s):  
Xenopus Oocytes ◽  
Cysteine Residue ◽  
Integral Membrane Proteins ◽  
Structural Domain ◽  
Nucleoside Transporter ◽  
Vasoactive Drugs ◽  
Wild Type ◽  
Functional Protein ◽  
Equilibrative Nucleoside Transporter ◽  
Transmembrane Segments

The human and rat equilibrative nucleoside transporter proteins hENT1, rENT1, hENT2 and rENT2 belong to a family of integral membrane proteins with 11 potential transmembrane segments (TMs), and are distinguished functionally by differences in transport of nucleobases and sensitivity to inhibition by nitrobenzylthioinosine (NBMPR) and vasoactive drugs. In the present study, we have produced recombinant hENT1, rENT1, hENT2 and rENT2 in Xenopus oocytes and investigated uridine transport following exposure to the impermeant thiol-reactive reagent p-chloromercuriphenyl sulphonate (PCMBS). PCMBS caused reversible inhibition of uridine influx by rENT2, but had no effect on hENT1, hENT2 or rENT1. This difference correlated with the presence in rENT2 of a unique Cys residue (Cys140) in the outer half of TM4 that was absent from the other ENTs. Mutation of Cys140 to Ser produced a functional protein (rENT2/C140S) that was insensitive to inhibition by PCMBS, identifying Cys140 as the exofacial Cys residue in rENT2 responsible for PCMBS inhibition. Uridine protected wild-type rENT2 against PCMBS inhibition, suggesting that Cys140 in TM4 lies within or is closely adjacent to the substrate-translocation channel of the transporter. TM4has been shown previously to be within a structural domain (TMs 3Ő6) responsible for interactions with NBMPR, vasoactive drugs and nucleobases.

scholarly journals Heterologous Expression of Mutated Eburicol 14α-Demethylase (CYP51) Proteins of Mycosphaerella graminicola To Assess Effects on Azole Fungicide Sensitivity and Intrinsic Protein Function

2010 ◽  
Vol 76 (9) ◽  
pp. 2866-2872 ◽  
Author(s):  
H. J. Cools ◽  
J. E. Parker ◽  
D. E. Kelly ◽  
J. A. Lucas ◽  
B. A. Fraaije ◽  
...  
Keyword(s):  
Amino Acid ◽  
Protein Function ◽  
Pathogenic Fungus ◽  
Mycosphaerella Graminicola ◽  
European Population ◽  
Wild Type ◽  
Gene Encoding ◽  
Intrinsic Protein ◽  
Western European ◽  
First Time

ABSTRACT The recent decrease in the sensitivity of the Western European population of the wheat pathogen Mycosphaerella graminicola to azole fungicides has been associated with the emergence and subsequent spread of mutations in the CYP51 gene, encoding the azole target sterol 14α-demethylase. In this study, we have expressed wild-type and mutated M. graminicola CYP51 (MgCYP51) variants in a Saccharomyces cerevisiae mutant carrying a doxycycline-regulatable tetO7 -CYC promoter controlling native CYP51 expression. We have shown that the wild-type MgCYP51 protein complements the function of the orthologous protein in S. cerevisiae. Mutant MgCYP51 proteins containing amino acid alterations L50S, Y459D, and Y461H and the two-amino-acid deletion ΔY459/G460, commonly identified in modern M. graminicola populations, have no effect on the capacity of the M. graminicola protein to function in S. cerevisiae. We have also shown that the azole fungicide sensitivities of transformants expressing MgCYP51 variants with these alterations are substantially reduced. Furthermore, we have demonstrated that the I381V substitution, correlated with the recent decline in the effectiveness of azoles, destroys the capacity of MgCYP51 to complement the S. cerevisiae mutant when introduced alone. However, when I381V is combined with changes between residues Y459 and Y461, the function of the M. graminicola protein is partially restored. These findings demonstrate, for the first time for a plant pathogenic fungus, the impacts that naturally occurring CYP51 alterations have on both azole sensitivity and intrinsic protein function. In addition, we also provide functional evidence underlying the order in which CYP51 alterations in the Western European M. graminicola population emerged.

scholarly journals Amino acid residue 247 in canine sulphotransferase SULT1D1: a new determinant of substrate selectivity

2004 ◽  
Vol 378 (2) ◽  
pp. 687-692 ◽  
Author(s):  
Carrie TSOI ◽  
Mikael WIDERSTEN ◽  
Ralf MORGENSTERN ◽  
Stellan SWEDMARK
Keyword(s):  
Amino Acid ◽  
Critical Role ◽  
Fold Increase ◽  
Binding Pocket ◽  
Amino Acid Residues ◽  
Wild Type ◽  
Substrate Binding Pocket ◽  
Site Selectivity ◽  
Km Value ◽  
Exogenous Compounds

The SULT (sulphotransferase) family plays a critical role in the detoxification and activation of endogenous and exogenous compounds as well as in the regulation of steroid hormone actions and neurotransmitter functions. The structure–activity relationships of the human SULTs have been investigated with focus on the amino acid 146 in hSULT1A3 and its impact on dopamine/PNP (p-nitrophenol) specificity. In the present study, we have generated canine SULT1D1 (cSULT1D1) variants with mutations at amino acid residues in the substrate-binding pocket [A146E (Ala-146→Glu), A146D, A146Q, I86D or D247L]. These mutation sites were chosen with regard to their possible contribution to the marked dopamine/PNP preference of cSULT1D1. After characterization, we found that the overall sulphation efficiencies for the cSULT1D1 A146 and the I86 mutants were strongly decreased for both substrates compared with wild-type cSULT1D1 but the substrate preference was unchanged. In contrast, the D247L mutant was found to be more than 21-fold better at sulphating PNP (120-fold decrease in Km value) but 54-fold less efficient in sulphating dopamine (8-fold increase in Km value) and the preference was switched from dopamine to PNP, indicating the importance of this amino acid in the dopamine/PNP preference in cSULT1D1. Our results show that Asp-247 has a pronounced effect on the substrate specificity of cSULT1D1 and thus we have identified a previously unrecognized contributor to active-site selectivity.

scholarly journals Nitrogen-regulated Ubiquitination of the Gap1 Permease ofSaccharomyces cerevisiae

1998 ◽  
Vol 9 (6) ◽  
pp. 1253-1263 ◽  
Author(s):  
Jean-Yves Springael ◽  
Bruno André
Keyword(s):  
Amino Acid ◽  
Nitrogen Source ◽  
Yeast Cells ◽  
Sole Nitrogen Source ◽  
Wild Type ◽  
Ammonium Ions ◽  
Amino Acid Permease ◽  
Rapid Inactivation ◽  
Subsequent Degradation ◽  
General Amino Acid Permease

Addition of ammonium ions to yeast cells growing on proline as the sole nitrogen source induces rapid inactivation and degradation of the general amino acid permease Gap1 through a process requiring the Npi1/Rsp5 ubiquitin (Ub) ligase. In this study, we show that NH4+induces endocytosis of Gap1, which is then delivered into the vacuole where it is degraded. This down-regulation is accompanied by increased conversion of Gap1 to ubiquitinated forms. Ubiquitination and subsequent degradation of Gap1 are impaired in thenpi1 strain. In this mutant, the amount of Npi1/Rsp5 Ub ligase is reduced >10-fold compared with wild-type cells. The C-terminal tail of Gap1 contains sequences, including a di-leucine motif, which are required for NH4+-induced internalization and degradation of the permease. We show here that mutant Gap1 permeases affected in these sequences still bind Ub. Furthermore, we provide evidence that only a small fraction of Gap1 is modified by Ub after addition of NH4+to mutants defective in endocytosis.

scholarly journals Augustine Blood Group System and Equilibrative Nucleoside Transporter 1

2021 ◽  
pp. 1-5
Author(s):  
Geoff Daniels
Keyword(s):  
Blood Group ◽  
Plasma Membranes ◽  
Ectopic Calcification ◽  
Blood Group System ◽  
Nucleoside Transporter ◽  
Haemolytic Disease ◽  
Equilibrative Nucleoside Transporter ◽  
Group System ◽  
Adenosine Transport

Augustine (AUG) is a blood group system comprising four antigens: AUG1, AUG2 (At<sup>a</sup>), and AUG4 are of very high frequency; AUG3 is of very low frequency. These antigens are located on ENT1, an equilibrative nucleoside transporter encoded by <i>SLC19A1</i>. AUG antibodies are of clinical relevance in blood transfusion and pregnancy: anti-AUG2 have caused haemolytic transfusion reactions; the only anti-AUG3 was associated with severe haemolytic disease of the fetus and newborn. ENT1 is present in almost all human tissues. It facilitates the transfer of purine and pyrimidine nucleosides and is responsible for the majority of adenosine transport across plasma membranes. Adenosine transport appears to be an important factor in the regulation of bone metabolism. The AUG<sub>null</sub> phenotype (AUG:–1,–2,–3,–4) has been found in three siblings, who are homozygous for an inactivating splice-site mutation in <i>SLC29A1</i>. Although ENT1 is very likely to be absent from all cells in these three individuals, they were apparently healthy with normal lifestyles. However, they suffered frequent attacks of pseudogout, a form of arthritis, in various joints with multiple calcifications around their hand joints. Ectopic calcification in the hips, pubic symphysis, and lumbar discs was present in the propositus. The three AUG<sub>null</sub> individuals had misshapen red cells with deregulated protein phosphorylation, but no anaemia or shortening of red cell lifespan. Defective in vitro erythropoiesis in the absence of ENT1 was confirmed by shRNA-mediated knockdown of ENT1 during in vitro erythropoiesis of CD34<sup>+</sup> progenitor cells from individuals with normal ENT1. Nucleoside transporters, such as ENT1, are vital in the uptake of synthetic nucleoside analogue drugs, used in cancer and viral chemotherapy. It is feasible that the efficacy of these drugs would be compromised in patients with the extremely rare AUG<sub>null</sub> phenotype.

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