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Analysis of the Topology and Active-Site Residues of WbbF, a Putative O-Polysaccharide Synthase from Salmonella enterica Serovar Borreze. J Bacteriol 2020; 202:JB.00625-19. [PMID: 31792013 DOI: 10.1128/jb.00625-19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 11/22/2019] [Indexed: 02/06/2023] Open
Abstract
Bacterial lipopolysaccharides are major components and contributors to the integrity of Gram-negative outer membranes. The more conserved lipid A-core part of this complex glycolipid is synthesized separately from the hypervariable O-antigenic polysaccharide (OPS) part, and they are joined in the periplasm prior to translocation to the outer membrane. Three different biosynthesis strategies are recognized for OPS biosynthesis, and one, the synthase-dependent pathway, is currently confined to a single example: the O:54 antigen from Salmonella enterica serovar Borreze. Synthases are complex enzymes that have the capacity to both polymerize and export bacterial polysaccharides. Although synthases like cellulose synthase are widespread, they typically polymerize a glycan without employing a lipid-linked intermediate, unlike the O:54 synthase (WbbF), which produces an undecaprenol diphosphate-linked product. This raises questions about the overall similarity between WbbF and conventional synthases. In this study, we examine the topology of WbbF, revealing four membrane-spanning helices, compared to the eight in cellulose synthase. Molecular modeling of the glycosyltransferase domain of WbbF indicates a similar architecture, and site-directed mutagenesis confirmed that residues important for catalysis and processivity in cellulose synthase are conserved in WbbF and required for its activity. These findings indicate that the glycosyltransferase mechanism of WbbF and classic synthases are likely conserved despite the use of a lipid acceptor for chain extension by WbbF.IMPORTANCE Glycosyltransferases play a critical role in the synthesis of a wide variety of bacterial polysaccharides. These include O-antigenic polysaccharides, which form the distal component of lipopolysaccharides and provide a protective barrier important for survival and host-pathogen interactions. Synthases are a subset of glycosyltransferases capable of coupled synthesis and export of glycans. Currently, the O:54 antigen of Salmonella enterica serovar Borreze involves the only example of an O-polysaccharide synthase, and its generation of a lipid-linked product differentiates it from classical synthases. Here, we explore features conserved in the O:54 enzyme and classical synthases to shed light on the structure and function of the unusual O:54 enzyme.
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Lu H, Cherepanova NA, Gilmore R, Contessa JN, Lehrman MA. Targeting STT3A-oligosaccharyltransferase with NGI-1 causes herpes simplex virus 1 dysfunction. FASEB J 2019; 33:6801-6812. [PMID: 30811219 DOI: 10.1096/fj.201802044rr] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Herpes simplex virus 1 (HSV-1) is a contagious neurotropic herpesvirus responsible for oral lesions and herpesviral encephalitis. The HSV-1 envelope contains N-glycosylated proteins involved in infection and that are candidate drug targets. NGI-1 is a small-molecule inhibitor of oligosaccharyltransferase (OST) complexes STT3A-OST and STT3B-OST, which catalyze cotranslational and post-translational N-glycosylation, respectively. Because host OSTs attach HSV-1 glycans, NGI-1 might have anti-HSV-1 activity. We evaluated HSV-1 function using NGI-1 and human embryonic kidney 293 knockout lines for OST isoform-specific catalytic and accessory subunits. N-glycosylation of 2 representative envelope proteins (gC and gD) was primarily dependent upon STT3A-OST, but to a large extent replaceable by STT3B-OST. Knockouts impairing STT3A- or STT3B-OST activity, by themselves, did not appreciably affect HSV-1 function (plaque-forming units, normalized to viral particles measured by unglycosylated capsid protein VP5 content). However, with cells lacking STT3B-OST activity (missing the catalytic subunit STT3B or the oxidoreductase subunits magnesium transporter 1/tumor suppressor candidate 3) and thus solely dependent upon STT3A-OST for N-glycosylation, NGI-1 treatment resulted in HSV-1 having cell type-dependent dysfunction (affecting infectivity with Vero cells much more than with the 293 lines). Ablation of post-translational N-glycosylation can therefore make HSV-1 infectivity, and possibly masking of immunogenic peptide epitopes by glycans, highly sensitive to pharmacological inhibition of cotranslational N-glycosylation.-Lu, H., Cherepanova, N. A., Gilmore, R., Contessa, J. N., Lehrman, M. A. Targeting STT3A-oligosaccharyltransferase with NGI-1 causes herpes simplex virus 1 dysfunction.
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Affiliation(s)
- Hua Lu
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Natalia A Cherepanova
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts, USA
| | - Reid Gilmore
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts, USA
| | - Joseph N Contessa
- Department of Therapeutic Radiology and Pharmacology, Yale School of Medicine, New Haven, Connecticut, USA.,Department of Pharmacology, Yale School of Medicine, New Haven, Connecticut, USA
| | - Mark A Lehrman
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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Geiser DL, Winzerling JJ. Insect transferrins: multifunctional proteins. Biochim Biophys Acta Gen Subj 2011; 1820:437-51. [PMID: 21810453 DOI: 10.1016/j.bbagen.2011.07.011] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2011] [Revised: 07/13/2011] [Accepted: 07/17/2011] [Indexed: 01/07/2023]
Abstract
BACKGROUND Many studies have been done evaluating transferrin in insects. Genomic analyses indicate that insects could have more than one transferrin. However, the most commonly studied insect transferrin, Tsf1, shows greatest homology to mammalian blood transferrin. SCOPE OF REVIEW Aspects of insect transferrin structure compared to mammalian transferrin and the roles transferrin serves in insects are discussed in this review. MAJOR CONCLUSIONS Insect transferrin can have one or two lobes, and can bind iron in one or both. The iron binding ligands identified for the lobes of mammalian blood transferrin are generally conserved in the lobes of insect transferrins that have an iron binding site. Available information supports that the form of dietary iron consumed influences the regulation of insect transferrin. Although message is expressed in several tissues in many insects, fat body is the likely source of hemolymph transferrin. Insect transferrin is a vitellogenic protein that is down-regulated by Juvenile Hormone. It serves a role in transporting iron to eggs in some insects, and transferrin found in eggs appears to be endowed from the female. In addition to the roles of transferrin in iron delivery, this protein also functions to reduce oxidative stress and to enhance survival of infection. GENERAL SIGNIFICANCE Future studies in Tsf1 as well as the other insect transferrins that bind iron are warranted because of the roles of transferrin in preventing oxidative stress, enhancing survival to infections and delivering iron to eggs for development. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.
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Affiliation(s)
- Dawn L Geiser
- Department of Nutritional Sciences, College of Agriculture and Life Sciences, The University of Arizona, Tucson, Arizona 85721, USA.
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Struwe WB, Hughes BL, Osborn DW, Boudreau ED, Shaw KMD, Warren CE. Modeling a congenital disorder of glycosylation type I in C. elegans: a genome-wide RNAi screen for N-glycosylation-dependent loci. Glycobiology 2009; 19:1554-62. [PMID: 19729382 PMCID: PMC2782245 DOI: 10.1093/glycob/cwp136] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Revised: 08/29/2009] [Accepted: 08/31/2009] [Indexed: 01/20/2023] Open
Abstract
Inefficient glycosylation caused by defective synthesis of lipid-linked oligosaccharide donor results in multi-systemic syndromes known as congenital disorders of glycosylation type I (CDG-I). Strong loss of function mutations are embryonic lethal, patients with partial losses of function are occasionally born but are very ill, presenting with defects in virtually every tissue. CDG-I clinical expression varies considerably and ranges from very mild to severe, and the underlying cause of the variable clinical features is not yet understood. We postulate that accompanying defects in an individual's genetic background enhance the severity of CDG-I clinical phenotypes. Since so many protein structures and functions are compromised in CDG-I illnesses, the gene products that are dependent on N-linked glycosylation which cause lethality or particular symptoms are difficult to resolve. The power of genetic silencing that is a characteristic of C. elegans has allowed us to systematically dissect the complex glycosylation phenotype observed in CDG-I patients into specific glycan-dependent gene products. To accomplish this, we inhibited glycosylation with a sub-phenotypic dose of tunicamycin, reduced single genes by RNA interference, and then sought loci where the combination caused a synthetic or dramatically enhanced phenotype. This screen has identified genes in C. elegans that require N-linked glycans to function properly as well as candidate gene homologues that may enhance the clinical severity of CDG-I disorders in humans.
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Affiliation(s)
- Weston B Struwe
- Department of Biochemistry and Molecular Biology, University of New Hampshire, Durham, NH 03824, USA.
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Rush JS, Gao N, Lehrman MA, Matveev S, Waechter CJ. Suppression of Rft1 expression does not impair the transbilayer movement of Man5GlcNAc2-P-P-dolichol in sealed microsomes from yeast. J Biol Chem 2009; 284:19835-42. [PMID: 19494107 DOI: 10.1074/jbc.m109.000893] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To further evaluate the role of Rft1 in the transbilayer movement of Man(5)GlcNAc(2)-P-P-dolichol (M5-DLO), a series of experiments was conducted with intact cells and sealed microsomal vesicles. First, an unexpectedly large accumulation (37-fold) of M5-DLO was observed in Rft1-depleted cells (YG1137) relative to Glc(3)Man(9)GlcNAc(2)-P-P-Dol in wild type (SS328) cells when glycolipid levels were compared by fluorophore-assisted carbohydrate electrophoresis analysis. When sealed microsomes from wild type cells and cells depleted of Rft1 were incubated with GDP-[(3)H]mannose or UDP-[(3)H]GlcNAc in the presence of unlabeled GDP-Man, no difference was observed in the rate of synthesis of [(3)H]Man(9)GlcNAc(2)-P-P-dolichol or Man(9)[(3)H]GlcNAc(2)-P-P-dolichol, respectively. In addition, no difference was seen in the level of M5-DLO flippase activity in sealed wild type and Rft1-depleted microsomal vesicles when the activity was assessed by the transport of GlcNAc(2)-P-P-Dol(15), a water-soluble analogue. The entry of the analogue into the lumenal compartment was confirmed by demonstrating that [(3)H]chitobiosyl units were transferred to endogenous peptide acceptors via the yeast oligosaccharyltransferase when sealed vesicles were incubated with [(3)H]GlcNAc(2)-P-P-Dol(15) in the presence of an exogenously supplied acceptor peptide. In addition, several enzymes involved in Dol-P and lipid intermediate biosynthesis were found to be up-regulated in Rft1-depleted cells. All of these results indicate that although Rft1 may play a critical role in vivo, depletion of this protein does not impair the transbilayer movement of M5-DLO in sealed microsomal fractions prepared from disrupted cells.
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Affiliation(s)
- Jeffrey S Rush
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, Kentucky 40536, USA
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Nakamura T, Ando A, Takagi H, Shima J. EOS1, whose deletion confers sensitivity to oxidative stress, is involved in N-glycosylation in Saccharomyces cerevisiae. Biochem Biophys Res Commun 2006; 353:293-8. [PMID: 17187761 DOI: 10.1016/j.bbrc.2006.12.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Accepted: 12/04/2006] [Indexed: 11/29/2022]
Abstract
The deletion strain of Saccharomyces cerevisiae YNL080c (designed as EOS1) was identified as a strain sensitive to high-sucrose stress in our previous report [A. Ando, F. Tanaka, Y. Murata, H. Takagi, J. Shima, Identification and classification of genes required for tolerance to high sucrose stress revealed by genome-wide screening of Saccharomyces cerevisiae, FEMS Yeast Res. 6 (2006) 249-267]. Delta eos1 showed higher sensitivity to oxidative stress than to high-sucrose stress. Immunofluorescence microscopic and cellular fractionation analyses suggested that Eos1 localizes in the endoplasmic reticulum membrane. We found that the deletion of EOS1 enhances tunicamycin tolerance and that in Delta eos1 the transcription level of KAR2, which is the ER stress-inducible gene, was much lower than that in the wild-type strain (BY4741) when exposed to tunicamycin. The inhibition of the N-glycosylation of carboxypeptidase Y and invertase activity caused by the addition of tunicamycin was depressed in Delta eos1, suggesting that EOS1 may be involved in N-glycosylation of the cellular proteins.
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Affiliation(s)
- Toshihide Nakamura
- National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan
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Harding HP, Zhang Y, Khersonsky S, Marciniak S, Scheuner D, Kaufman RJ, Javitt N, Chang YT, Ron D. Bioactive small molecules reveal antagonism between the integrated stress response and sterol-regulated gene expression. Cell Metab 2005; 2:361-71. [PMID: 16330322 PMCID: PMC1361344 DOI: 10.1016/j.cmet.2005.11.005] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Revised: 08/08/2005] [Accepted: 11/09/2005] [Indexed: 10/25/2022]
Abstract
Phosphorylation of translation initiation factor 2alpha (eIF2alpha) coordinates a translational and transcriptional program known as the integrated stress response (ISR), which adapts cells to endoplasmic reticulum (ER) stress. A screen for small molecule activators of the ISR identified two related compounds that also activated sterol-regulated genes by blocking cholesterol biosynthesis at the level of CYP51. Ketoconazole, a known CYP51 inhibitor, had similar effects, establishing that perturbed flux of precursors to cholesterol activates the ISR. Surprisingly, compound-mediated activation of sterol-regulated genes was enhanced in cells with an ISR-blocking mutation in the regulatory phosphorylation site of eIF2alpha. Furthermore, induction of the ISR by an artificial drug-activated eIF2alpha kinase reduced the level of active sterol regulatory element binding protein (SREBP) and sterol-regulated mRNAs. These findings suggest a mechanism by which interactions between sterol metabolism, the ISR, and the SREBP pathway affect lipid metabolism during ER stress.
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Affiliation(s)
- Heather P. Harding
- Skirball Institute of Biomolecular Medicine
- Department of Pharmacology
- *Correspondence: (H.P.H.); (D.R.)
| | | | - Sonya Khersonsky
- Department of Chemistry, New York University, New York, New York 10003
| | | | - Donalyn Scheuner
- Department of Biochemistry, University of Michigan School of Medicine, Ann Arbor, Michigan 48109
| | - Randal J. Kaufman
- Department of Biochemistry, University of Michigan School of Medicine, Ann Arbor, Michigan 48109
| | | | - Young-Tae Chang
- Department of Chemistry, New York University, New York, New York 10003
| | - David Ron
- Skirball Institute of Biomolecular Medicine
- Department of Medicine
- Department of Cell Biology New York University School of Medicine, New York, New York 10016
- *Correspondence: (H.P.H.); (D.R.)
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8
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Rush JS, Waechter CJ. Assay for the transbilayer movement of polyisoprenoid-linked saccharides based on the transport of water-soluble analogues. Methods 2005; 35:316-22. [PMID: 15804602 DOI: 10.1016/j.ymeth.2004.10.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/20/2004] [Indexed: 10/25/2022] Open
Abstract
Flippases are a class of membrane proteins that are proposed to facilitate the transbilayer movement of amphipathic polar lipids that are required for membrane biogenesis and the assembly of many diverse complex glycoconjugates in eukaryotic and prokaryotic cells. Despite their crucial roles in membrane biology, very little is known about their structures and the precise mechanism(s) by which they overcome the biophysical barriers of the hydrophobic core, and allow polar head groups to traverse membrane bilayers. This chapter presents methods based on the transport of water-soluble analogues that can be applied to investigate membrane proteins mediating the transverse diffusion of polyisoprenoid-linked glycolipid intermediates involved in the biosynthesis of N-linked glycoproteins, glycosylphosphatidylinositol anchors and bacterial polysaccharides.
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Affiliation(s)
- Jeffrey S Rush
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY 40536, USA
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9
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Bickel T, Lehle L, Schwarz M, Aebi M, Jakob CA. Biosynthesis of lipid-linked oligosaccharides in Saccharomyces cerevisiae: Alg13p and Alg14p form a complex required for the formation of GlcNAc(2)-PP-dolichol. J Biol Chem 2005; 280:34500-6. [PMID: 16100113 DOI: 10.1074/jbc.m506358200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
N-Glycosylation in the endoplasmic reticulum is an essential protein modification and highly conserved in evolution from yeast to man. Here we identify and characterize two essential yeast proteins having homology to bacterial glycosyltransferases, designated Alg13p and Alg14p, as being required for the formation of GlcNAc(2)-PP-dolichol (Dol), the second step in the biosynthesis of the unique lipid-linked core oligosaccharide. Down-regulation of each gene led to a defect in protein N-glycosylation and an accumulation of GlcNAc(1)-PP-Dol in vivo as revealed by metabolic labeling with [(3)H]glucosamine. Microsomal membranes from cells repressed for ALG13 or ALG14, as well as detergent-solubilized extracts thereof, were unable to catalyze the transfer of N-acetylglucosamine from UDP-GlcNAc to [(14)C]GlcNAc(1)-PP-Dol, but did not impair the formation of GlcNAc(1)-PP-Dol or GlcNAc-GPI. Immunoprecipitating Alg13p from solubilized extracts resulted in the formation of GlcNAc(2)-PP-Dol but required Alg14p for activity, because an Alg13p immunoprecipitate obtained from cells in which ALG14 was down-regulated lacked this activity. In Western blot analysis it was demonstrated that Alg13p, for which no well defined transmembrane segment has been predicted, localizes both to the membrane and cytosol; the latter form, however, is enzymatically inactive. In contrast, Alg14p is exclusively membrane-bound. Repression of the ALG14 gene causes a depletion of Alg13p from the membrane. By affinity chromatography on IgG-Sepharose using Alg14-ZZ as bait, we demonstrate that Alg13-myc co-fractionates with Alg14-ZZ. The data suggest that Alg13p associates with Alg14p to a complex forming the active transferase catalyzing the biosynthesis of GlcNAc(2)-PP-Dol.
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Affiliation(s)
- Tanja Bickel
- Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
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10
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Rick PD, Barr K, Sankaran K, Kajimura J, Rush JS, Waechter CJ. Evidence that the wzxE gene of Escherichia coli K-12 encodes a protein involved in the transbilayer movement of a trisaccharide-lipid intermediate in the assembly of enterobacterial common antigen. J Biol Chem 2003; 278:16534-42. [PMID: 12621029 DOI: 10.1074/jbc.m301750200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The assembly of many bacterial cell surface polysaccharides requires the transbilayer movement of polyisoprenoid-linked saccharide intermediates across the cytoplasmic membrane. It is generally believed that transverse diffusion of glycolipid intermediates is mediated by integral membrane proteins called translocases or "flippases." The bacterial genes proposed to encode these translocases have been collectively designated wzx genes. The wzxE gene of Escherichia coli K-12 has been implicated in the transbilayer movement of Fuc4NAc-ManNAcA-GlcNAc-P-P-undecaprenol (lipid III), the donor of the trisaccharide repeat unit in the biosynthesis of enterobacterial common antigen (ECA). Previous studies (Feldman, M. F., Marolda, C. L., Monteiro, M. A., Perry, M. B., Parodi, A. J., and Valvano, M. (1999) J. Biol. Chem. 274, 35129-35138) provided indirect evidence that the wzx(016) gene product of E. coli K-12 encoded a translocase capable of mediating the transbilayer movement of N-acetylglucosaminylpyrophosphorylundecaprenol (GlcNAc-P-P-Und), an early intermediate in the synthesis of ECA and many lipopolysaccharide O antigens. Therefore, genetic and biochemical studies were conducted to determine if the putative Wzx(O16) translocase was capable of mediating the transport of N-acetylglucosaminylpyrophosphorylnerol (GlcNAc-P-P-Ner), a water-soluble analogue of GlcNAc-P-P-Und. [(3)H]GlcNAc-P-P-Ner was transported into sealed, everted cytoplasmic membrane vesicles of E. coli K-12 as well as a deletion mutant lacking both the wzx(016) and wzxC genes. In contrast, [(3)H]GlcNAc-P-P-Ner was not transported into membrane vesicles prepared from a wzxE-null mutant, and metabolic radiolabeling experiments revealed the accumulation of lipid III in this mutant. The WzxE transport system exhibited substrate specificity by recognizing both a pyrophosphoryl-linked saccharide and an unsaturated alpha-isoprene unit in the carrier lipid. These results support the conclusion that the wzxE gene encodes a membrane protein involved in the transbilayer movement of lipid III in E. coli.
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Affiliation(s)
- Paul D Rick
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA.
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11
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Gao N, Lehrman MA. Coupling of the dolichol-P-P-oligosaccharide pathway to translation by perturbation-sensitive regulation of the initiating enzyme, GlcNAc-1-P transferase. J Biol Chem 2002; 277:39425-35. [PMID: 12176988 DOI: 10.1074/jbc.m205195200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In mammalian cells, inhibition of translation interferes with synthesis of the lipid-linked oligosaccharide (LLO) Glc3Man9GlcNAc2-P-P-dolichol as measured with radioactive sugar precursors. Conflicting hypotheses have been proposed, and the fundamental basis for this regulation has remained elusive. Here, fluorophore-assisted carbohydrate electrophoresis (FACE) was used to measure LLO concentrations directly in cells treated with translation blockers. Further, LLO biosynthetic enzymes were assayed in vitro with endogenous acceptor substrates using either cells gently permeabilized with streptolysin-O (SLO) or microsomes from homogenized cells. In Chinese hamster ovary (CHO)-K1 cells treated with translation blockers, FACE did not detect changes in concentrations of Glc3Man9GlcNAc2-P-P-dolichol or early LLO intermediates. These results do not support earlier proposals for feedback repression of LLO initiation by accumulated Glc3Man9GlcNAc2-P-P-dolichol, or inhibition of a GDP-mannose dependent transferase. With microsomes from cells treated with translation blockers, there was no interference with LLO initiation by GlcNAc-1-P transferase (GPT), mannose-P-dolichol synthase, glucose-P-dolichol synthase, or LLO synthesis in vitro, as reported previously. Surprisingly, inhibition of all of these was detected with the SLO in vitro system. Additional experiments with the SLO system showed that the three transferases shared a limited pool of dolichol-P that was trapped as Glc3Man9GlcNAc2-P-P-dolichol by translation arrest. Overexpression of GPT was unable to reverse the effects of translation arrest on LLO initiation, and experiments with FACE and the SLO system showed that overexpressed GPT was not functional in vivo, although it was highly active in microsomal assays. Thus, the combined use of the SLO in vitro system and FACE showed that LLO biosynthesis depends upon a limited primary pool of dolichol-P. Physical perturbation associated with microsome preparation appears to make available a secondary pool of dolichol-P, masking inhibition by translation arrest, as well as activating a nonfunctional fraction of GPT. The implications of these results for the organization of the LLO pathway are discussed.
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Affiliation(s)
- Ningguo Gao
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041, USA
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12
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Metzler DE, Metzler CM, Sauke DJ. Some Pathways of Carbohydrate Metabolism. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50023-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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13
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Dal Nogare AR, Dan N, Lehrman MA. Conserved sequences in enzymes of the UDP-GlcNAc/MurNAc family are essential in hamster UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase. Glycobiology 1998; 8:625-32. [PMID: 9592129 DOI: 10.1093/glycob/8.6.625] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The UDP-GlcNAc/MurNAc family of eukaryotic and prokaryotic enzymes use UDP-GlcNAc or UDP-MurNAc-pentapeptide as donors, dolichol-P or polyprenol-P as acceptors, and generate sugar-P-P-polyisoprenols. A series of six conserved sequences, designated A through F and ranging from 5 to 13 amino acid residues, has been identified in this family. To determine whether these conserved sequences are required for enzyme function, various mutations were examined in hamster UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT). Scramble mutations of sequences B-F, generated by scrambling the residues within each sequence, demonstrated that each is important in GPT. While E and F scrambles appeared to prevent stable expression of GPT, scrambling of B-D resulted in GPT mutants that could be stably expressed and bound tunicamycin, but lacked enzymatic activity. Further, the C and D scramble mutants had an unexpected sorting defect. Replacement of sequences B-F with prokaryotic counterparts from either the B.subtilis mraY or E.coli rfe genes also affected GPT by preventing expression of the mutant protein (B, F) or inhibiting its enzymatic activity (C-E). For the C-E replacements, no acquisition of acceptor activity for polyprenol-P, the fully unsaturated natural bacterial acceptor, was detected. These studies show that the conserved sequences of the UDP-GlcNAc/MurNAc family are important, and that the eukaryotic and prokaryotic counterparts are not freely interchangeable. Since several mutants were efficiently expressed and bound tunicamycin, yet lacked enzymatic activity, the data are consistent with these sequences having a direct role in product formation.
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Affiliation(s)
- A R Dal Nogare
- Departments of Internal Medicine and Pharmacology, University of Texas Southwestern Medical Center At Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75235-9041, USA
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Dan N, Lehrman MA. Oligomerization of hamster UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase, an enzyme with multiple transmembrane spans. J Biol Chem 1997; 272:14214-9. [PMID: 9162053 DOI: 10.1074/jbc.272.22.14214] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Hamster UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT), which initiates N-linked glycosylation by catalyzing the synthesis of GlcNAc-P-P-dolichol, has multiple transmembrane spans and a catalytic site that probably exists on the cytosolic face of the endoplasmic reticulum membrane (Dan, N., Middleton, R. M., and Lehrman, M. A. (1996) J. Biol. Chem. 271, 30717-30725). In this report, we demonstrate that GPT forms functional oligomers, probably dimers. Oligomers were detected by chemical cross-linking of GPT and by a dominant-negative effect caused by co-expression of enzymatically inactive (but properly folded) GPT mutants. The GPT mutants had no effect on two other dolichol-P-dependent endoplasmic reticulum enzymes. Mixing experiments indicated that mature GPT was competent for oligomerization. Oligomerization appeared to be favored in detergent extracts compared with intact microsomes. Detergent treatments were found to prevent, rather than promote, nonspecific aggregation of GPT. These results demonstrate that GPT subunits can physically interact and influence each other. The implications of oligomerization for enzyme function are discussed. From these results, we conclude that GPT is one of a very small number of multitransmembrane span enzymes that can form multimers.
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Affiliation(s)
- N Dan
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9041, USA
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Dan N, Middleton RB, Lehrman MA. Hamster UDP-N-acetylglucosamine:dolichol-P N-acetylglucosamine-1-P transferase has multiple transmembrane spans and a critical cytosolic loop. J Biol Chem 1996; 271:30717-24. [PMID: 8940049 DOI: 10.1074/jbc.271.48.30717] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT) is an endoplasmic reticulum (ER) enzyme responsible for synthesis of GlcNAc-P-P-dolichol, the committed step of dolichol-P-P-oligosaccharide synthesis. The sequence of hamster GPT predicted multiple transmembrane segments (Zhu, X., and Lehrman, M. A. (1990) J. Biol. Chem. 265, 14250-14255). GPT has also been predicted to act on the cytosolic face of the ER membrane, based on topological studies of its substrates and products. In this report we test these predictions by: (i) immunofluorescence microscopy with antibodies specific for native GPT sequences or epitope tags inserted into GPT, after selective permeabilization of the plasma membrane with digitonin; (ii) insertion of Factor Xa cleavage sites; (iii) in vitro translation of GPT; and (iv) site-directed mutagenesis. The loops between the 1st and 2nd and between the 9th and 10th predicted transmembrane spans of GPT were found to be cytosolic. In contrast, the loop between the 6th and 7th transmembrane spans, as well as the carboxyl terminus, were lumenal. Thus, hamster GPT must cross the ER membrane at least three times, consistent with previous computer-assisted predictions. There was no apparent N-glycosylation or signal sequence cleavage detected by in vitro translation. The cytosolic loop between the 9th and 10th transmembrane spans is the largest hydrophilic segment in GPT and, as judged by site-directed mutagenesis, has a number of conserved residues essential for activity. Hence, these results directly support the hypothesis that dolichol-P-P-oligosaccharide assembly is initiated in the cytosol and that a downstream intermediate must translocate to the lumenal face of the ER membrane.
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Affiliation(s)
- N Dan
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9041, USA.
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Hiss D, Gabriels G, Jacobs P, Folb P. Tunicamycin potentiates drug cytotoxicity and vincristine retention in multidrug resistant cell lines. Eur J Cancer 1996; 32A:2164-72. [PMID: 9014761 DOI: 10.1016/s0959-8049(96)00262-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Tunicamycin (TM), an inhibitor of glycoprotein processing, was investigated for its potential to reverse the multiple drug resistance (MDR) phenotype. When TM was added in vitro to drug-resistant NIH-3T3-MDR and KB-8-5-11 cells, they developed an increased sensitivity to doxorubicin, epirubicin, vincristine and colchicine. Similarly, the sensitivity of NIH-3T3-MDR cells to cisplatin was also enhanced by TM. In the presence of TM, drug-sensitive NIH-3T3-parental cells exhibited greater susceptibility to the toxic effects of doxorubicin, epirubicin, vincristine (marginally significant), and colchicine, but not to cisplatin. Tunicamycin-treated drug-sensitive KB-3-1 cells showed an increased response to vincristine, but not to the other anticancer drugs. Pretreatment with TM inhibited glycoprotein synthesis in all the cell lines. Neither prior exposure to, nor co-incubation with TM, influenced the uptake of vincristine (VCR) in the various cell lines. However, NIH-3T3-MDR cells accumulated less VCR than their drug-sensitive controls and also exhibited reduced efflux of the drug when treated with TM. There were no significant differences in the levels of intracellular VCR uptake between drug-sensitive KB-3-1 and KB-8-5-11 cells. Tunicamycin increased intracellular VCR retention in KB-8-5-11 and NIH-3T3-MDR cells, but not in NIH-3T3-parental cells. However, drug-sensitive KB-3-1 cells expressed reduced VCR retention in response to TM exposure, indicating that correlations between VCR toxicity and its retention in the presence of TM should be made with caution. The results suggest that the enhancement of intracellular VCR retention in MDR cells lines caused by TM is likely to be the result of inhibition of VCR efflux. Inhibition of glycoprotein synthesis during TM exposure may account for the changes in VCR efflux and retention observed in the MDR cell lines. The enhancement of cisplatin cytotoxicity in NIH-3T3-MDR cells after exposure to TM is an interesting observation, since it is generally believed that agents which modify the MDR phenotype do not show a sensitising effect to cisplatin. These findings may have applications in the reversal of drug resistance.
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Affiliation(s)
- D Hiss
- Department of Pharmacology, University of Cape Town, Medical School, South Africa
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Zeng Y, Elbein AD. UDP-N-acetylglucosamine:dolichyl-phosphate N-acetylglucosamine-1-phosphate transferase is amplified in tunicamycin-resistant soybean cells. EUROPEAN JOURNAL OF BIOCHEMISTRY 1995; 233:458-66. [PMID: 7588788 DOI: 10.1111/j.1432-1033.1995.458_2.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A tunicamycin-resistant soybean cell line was developed by gradually increasing the concentration of tunicamycin in the growth medium. At the final stage, the resistant cells could survive in media containing 60 micrograms/ml of tunicamycin, whereas normal cells show a greatly retarded growth rate at 0.5 microgram/ml of antibiotic. The tunicamycin-resistant cells had a greater than 40-fold increase in the activity of the enzyme UDP-GlcNAc:dolichyl-P GlcNAc1P transferase, a 2-3-fold increase in the activity of dolichyl-P-mannose synthase, but no increase in the activities of other enzymes of the lipid-linked saccharide pathway such as dolichyl-P-glucose synthase or mannosyl transferases. There was also no change in the activities of the glycoprotein-processing enzymes, glucosidase I or glucosidase II, as compared to wild-type cells. The increase in GlcNAc1P transferase was due to an increased production of enzyme, as seen by a dramatic increase in the amount of a 39-kDa protein, which is presumed to be this enzyme protein. The GlcNAc1P transferase from tunicamycin-resistant cells was equally sensitive to tunicamycin as was the wild-type enzyme, but was considerably more labile to temperatures above 30 degrees C. The activity in tunicamycin-resistant cells was greatly stimulated by exogenous dolichyl-P. The spectrum of oligosaccharides from labeled lipid-linked oligosaccharides was similar in wild-type and tunicamycin-resistant soybean cells, but the resistant cells had significantly greater amounts of the shorter and much lower amounts of the larger-sized oligosaccharides.
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Affiliation(s)
- Y Zeng
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205, USA
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Ware FE, Vassilakos A, Peterson PA, Jackson MR, Lehrman MA, Williams DB. The molecular chaperone calnexin binds Glc1Man9GlcNAc2 oligosaccharide as an initial step in recognizing unfolded glycoproteins. J Biol Chem 1995; 270:4697-704. [PMID: 7876241 DOI: 10.1074/jbc.270.9.4697] [Citation(s) in RCA: 337] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Calnexin is a molecular chaperone that resides in the membrane of the endoplasmic reticulum. Most proteins that calnexin binds are N-glycosylated, and treatment of cells with tunicamycin or inhibitors of initial glucose trimming steps interferes with calnexin binding. To test if calnexin is a lectin that binds early oligosaccharide processing intermediates, a recombinant soluble calnexin was created. Incubation of soluble calnexin with a mixture of Glc0-3Man9GlcNAc2 oligosaccharides resulted in specific binding of the Glc1Man9GlcNAc2 species. Furthermore, Glc1Man5-7GlcNAc2 oligosaccharides bound relatively poorly, suggesting that, in addition to a requirement for the single terminal glucose residue, at least one of the terminal mannose residues was important for binding. To assess the involvement of oligosaccharide-protein interactions in complexes of calnexin and newly synthesized glycoproteins, alpha 1-antitrypsin or the heavy chain of the class I histocompatibility molecule were purified as complexes with calnexin and digested with endoglycosidase H. All oligosaccharides on either glycoprotein were accessible to this probe and could be removed without disrupting the association with calnexin. Furthermore, the addition of 1 M alpha-methyl glucoside or alpha-methyl mannoside had no effect on complex stability. These findings suggest that once complexes between calnexin and glycoproteins are formed, oligosaccharide binding does not contribute significantly to the overall interaction. However, it is likely that the binding of Glc1Man9GlcNAc2 oligosaccharides is a crucial event during the initial recognition of newly synthesized glycoproteins by calnexin.
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Affiliation(s)
- F E Ware
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235-9041
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Chapter 5 Biosynthesis 2a. The Coenzymic Role of Phosphodolichols. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s0167-7306(08)60590-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Role of the carboxyl terminus in stable expression of hamster UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32281-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Rajput B, Muniappa N, Vijay I. Developmental and hormonal regulation of UDP-GlcNAc:dolichol phosphate GlcNAc-1-P transferase in mouse mammary gland. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)33972-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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Crick D, Scocca J, Rush J, Frank D, Krag S, Waechter C. Induction of dolichyl-saccharide intermediate biosynthesis corresponds to increased long chain cis-isoprenyltransferase activity during the mitogenic response in mouse B cells. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)34096-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Camp L, Chauhan P, Farrar J, Lehrman M. Defective mannosylation of glycosylphosphatidylinositol in Lec35 Chinese hamster ovary cells. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53309-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Slonina A, Scott T, Lehrman M. Gene inactivation in Lec35.1 (mannosylation-defective) Chinese hamster ovary cells. A cautionary note. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53310-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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