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Stelzl T, Geillinger-Kästle KE, Stolz J, Daniel H. Glycans in the intestinal peptide transporter PEPT1 contribute to function and protect from proteolysis. Am J Physiol Gastrointest Liver Physiol 2017; 312:G580-G591. [PMID: 28336547 DOI: 10.1152/ajpgi.00343.2016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 03/16/2017] [Accepted: 03/17/2017] [Indexed: 01/31/2023]
Abstract
Despite the fact that many membrane proteins carry extracellular glycans, little is known about whether the glycan chains also affect protein function. We recently demonstrated that the proton-coupled oligopeptide transporter 1 (PEPT1) in the intestine is glycosylated at six asparagine residues (N50, N406, N439, N510, N515, and N532). Mutagenesis-induced disruption of the individual N-glycosylation site N50, which is highly conserved among mammals, was detected to significantly enhance the PEPT1-mediated inward transport of peptides. Here, we show that for the murine protein the inhibition of glycosylation at sequon N50 by substituting N50 with glutamine, lysine, or cysteine or by replacing S52 with alanine equally altered PEPT1 transport kinetics in oocytes. Furthermore, we provide evidence that the uptake of [14C]glycyl-sarcosine in immortalized murine small intestinal (MODE-K) or colonic epithelial (PTK-6) cells stably expressing the PEPT1 transporter N50Q is also significantly increased relative to the wild-type protein. By using electrophysiological recordings and tracer flux studies, we further demonstrate that the rise in transport velocity observed for PEPT1 N50Q is bidirectional. In line with these findings, we show that attachment of biotin derivatives, comparable in weight with two to four monosaccharides, to the PEPT1 N50C transporter slows down the transport velocity. In addition, our experiments provide strong evidence that glycosylation of PEPT1 confers resistance against proteolytic cleavage by proteinase K, whereas a remarkable intrinsic stability against trypsin, even in the absence of N-linked glycans, was detected.NEW & NOTEWORTHY This study highlights the role of N50-linked glycans in modulating the bidirectional transport activity of the murine peptide transporter PEPT1. Electrophysiological and tracer flux measurements in Xenopus oocytes have shown that removal of the N50 glycans increases the maximal peptide transport rate in the inward and outward directions. This effect could be largely reversed by replacement of N50 glycans with structurally dissimilar biotin derivatives. In addition, N-glycans were detected to stabilize PEPT1 against proteolytic cleavage.
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Affiliation(s)
- Tamara Stelzl
- Nutritional Physiology, Technische Universität München, Freising, Germany
| | | | - Jürgen Stolz
- Nutritional Physiology, Technische Universität München, Freising, Germany
| | - Hannelore Daniel
- Nutritional Physiology, Technische Universität München, Freising, Germany
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Bunse S, Schmidt M, Prochnow N, Zoidl G, Dermietzel R. Intracellular cysteine 346 is essentially involved in regulating Panx1 channel activity. J Biol Chem 2010; 285:38444-52. [PMID: 20829356 DOI: 10.1074/jbc.m110.101014] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Pannexins constitute a family of proteins exhibiting predominantly hemichannel activity. Pannexin channels have been suggested to participate in a wide spectrum of biological functions such as propagation of calcium waves, release of IL-1β, and responses to ischemic conditions. At present, the molecular mechanisms regulating pannexin hemichannel activity are essentially unknown. Because cysteines have been shown to constitute key elements in regulating hemichannel properties of the connexin-type we performed site-directed mutagenesis of intracellular cysteine residues of Panx1. Cysteine to serine exchange (Cys → Ser) at the C-terminal position amino acid 346 led to a constitutively leaky hemichannel and subsequently to cell death. Increased channel activity was demonstrated by dye uptake and electrophysiological profiling in injected Xenopus laevis oocytes and transfected N2A cells. Mutations of the remaining intracellular cysteines did not result in major changes of Panx1 channel properties. From these data we conclude that the Cys-346 residue is important for proper functioning of the Panx1 channel.
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Affiliation(s)
- Stefanie Bunse
- Department of Neuroanatomy and Molecular Brain Research, Ruhr-University Bochum, 44780 Bochum, Germany
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Boassa D, Ambrosi C, Qiu F, Dahl G, Gaietta G, Sosinsky G. Pannexin1 channels contain a glycosylation site that targets the hexamer to the plasma membrane. J Biol Chem 2007; 282:31733-43. [PMID: 17715132 DOI: 10.1074/jbc.m702422200] [Citation(s) in RCA: 221] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Pannexins are newly discovered channel proteins expressed in many different tissues and abundantly in the vertebrate central nervous system. Based on membrane topology, folding and secondary structure prediction, pannexins are proposed to form gap junction-like structures. We show here that Pannexin1 forms a hexameric channel and reaches the cell surface but, unlike connexins, is N-glycosylated. Using site-directed mutagenesis we analyzed three putative N-linked glycosylation sites and examined the effects of each mutation on channel expression. We show for the first time that Pannexin1 is glycosylated at Asn-254 and that this residue is important for plasma membrane targeting. The glycosylation of Pannexin1 at its extracellular surface makes it unlikely that two oligomers could dock to form an intercellular channel. Ultrastructural analysis by electron microscopy confirmed that Pannexin1 junctional areas do not appear as canonical gap junctions. Rather, Pannexin1 channels are distributed throughout the plasma membrane. We propose that N-glycosylation of Pannexin1 could be a significant mechanism for regulating the trafficking of these membrane proteins to the cell surface in different tissues.
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Affiliation(s)
- Daniela Boassa
- National Center for Microscopy and Imaging Research, Center for Research in Biological Systems, Department of Neurosciences, University of California, San Diego, La Jolla, California 92093-0608, USA.
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Colpitts TL, Billing-Medel P, Friedman P, Granados EN, Hayden M, Hodges S, Menhart N, Roberts L, Russell J, Stroupe SD. Mammaglobin is found in breast tissue as a complex with BU101. Biochemistry 2001; 40:11048-59. [PMID: 11551201 DOI: 10.1021/bi010284f] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The mammaglobin gene has been shown to be preferentially expressed in breast tissue. Few genes match its specificity. Mammaglobin has generated much interest, and studies are ongoing to develop diagnostic tests for breast cancer based on the detection of mammaglobin. While searching the Incyte Genomics Lifeseq database for tissue-specific markers, we observed a second secretoglobin, BU101, also known as lipophilin B. We report here that mammaglobin, in breast tissue, is found as a complex with BU101. The complex was isolated from breast cancer tissue and was characterized as the biologically relevant form of mammaglobin.
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Affiliation(s)
- T L Colpitts
- Breast Cancer Venture, Abbott Diagnostics Division, Abbott Laboratories, Abbott Park, Illinois 60064, USA
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Colpitts TL, Billing P, Granados E, Hodges S, Menhart N, Russell J, Stroupe S. Mammaglobin complexes with BU101 in breast tissue. Ann N Y Acad Sci 2001; 923:312-5. [PMID: 11193768 DOI: 10.1111/j.1749-6632.2000.tb05540.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- T L Colpitts
- Breast Cancer Venture, Department 90M, AP20, 100 Abbott Park Road, Abbott Park, IL 60064-6015, USA.
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Musshoff U, Madeja M, Bloms P, Müsch-Nittel K, Speckmann EJ. Tunicamycin-induced inhibition of functional expression of glutamate receptors in Xenopus oocytes. Neurosci Lett 1992; 147:163-6. [PMID: 1283456 DOI: 10.1016/0304-3940(92)90585-u] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The effects of tunicamycin, a specific inhibitor of N-linked glycosylation, on functional expression of glutamate receptor subtypes were investigated in RNA-injected oocytes. In the presence of tunicamycin the expression of ligand-operated receptors sensitive to kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and quisqualate were completely blocked. The inhibitory effect was reversible after removal of tunicamycin from the culture medium.
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Buller AL, White MM. Altered patterns of N-linked glycosylation of the Torpedo acetylcholine receptor expressed in Xenopus oocytes. J Membr Biol 1990; 115:179-89. [PMID: 2355395 DOI: 10.1007/bf01869456] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The nicotinic acetylcholine receptor (AChR) from Torpedo electroplax is an oligomeric transmembrane glycoprotein made up of four highly homologous subunits in a stoichiometry of alpha 2 beta gamma delta. The role of N-linked glycosylation of the AChR has been studied in several cell lines and these studies have suggested that the addition of carbohydrate may be important for receptor expression. While Xenopus oocytes have proven to be an invaluable tool for studying the AChR, little is known about N-linked glycosylation of the oocyte-expressed receptor. The present report demonstrates that the oocyte-expressed AChR is glycosylated and contains the same number of oligosaccharide residues per subunit as the native receptor. However, unlike the native Torpedo receptor which contains both high mannose and complex oligosaccharides, the oocyte-expressed AChR contains only high mannose oligosaccharide modifications. However, as has been well documented, the Torpedo AChR expressed in oocytes is fully functional, demonstrating that the precise nature of the oligosaccharide modification is not critical for receptor function. The role of the oligosaccharide component of the AChR in receptor function was examined using tunicamycin (TM) to inhibit N-linked protein glycosylation. TM treatment resulted in a 70-80% inhibition of AChR expression in oocytes. Functional, unglycosylated receptors were not expressed; receptors expressed in TM-treated oocytes were functional wild-type, glycosylated AChR, formed only during the initial 12 hr of TM exposure. These data suggest that while glycosylation of the oocyte-expressed Torpedo AChR is required for assembly of subunits into a functional receptor, as has been demonstrated in other cells, oocyte modification of normal Torpedo glycosylation patterns does not affect receptor function or assembly.
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Affiliation(s)
- A L Buller
- Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia 19104
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The role of cytosolic and membrane factors in processing of the human beta-2 adrenergic receptor following translocation and glycosylation in a cell-free system. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39158-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
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9
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Roitsch T, Lehle L. Expression of yeast invertase in oocytes from Xenopus laevis. Secretion of active enzyme differing in glycosylation. EUROPEAN JOURNAL OF BIOCHEMISTRY 1989; 181:733-9. [PMID: 2659349 DOI: 10.1111/j.1432-1033.1989.tb14785.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
In an effort to understand factors that control glycosylation of proteins and processing of carbohydrate chains, invertase from Saccharomyces cerevisiae was expressed in a heterologous system. Microinjection of invertase-specific in vitro transcripts into oocytes from Xenopus laevis resulted in synthesis, glycosylation and secretion of enzymatically active invertase. It was found that although the number of carbohydrate chains acquired is the same as in yeast, the carbohydrate processing is different. This is consistent with the notion that the usage of a glycosylation site is determined by the protein part, whereas subsequent processing occurs in a host-dependent manner. Both, high-mannose and complex type glycans, most likely tri- and tetra-antennary structures, were synthesized in oocytes. The data obtained suggests that in this system the core chains of yeast invertase remain high-mannose type, whereas the more extensively processed polymannose chains are modified to complex oligosaccharides. In the presence of the glycosylation inhibitor, tunicamycin, and the glucosidase processing inhibitor, methyldeoxynojirimycin, secretion of invertase is significantly decreased, whereas in the presence of the mannosidase inhibitor, deoxymannojirimycin, no influence of secretion is seen. This may suggest that glycosylation of invertase is important for early secretion events. Expression of invertase lacking the leader sequence results in loss of glycosylation and secretion in oocytes. This indicates that yeast signals for secretion are functional in this higher eukaryote.
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Affiliation(s)
- T Roitsch
- Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, Federal Republic of Germany
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10
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Human low density lipoprotein receptor expressed in Xenopus oocytes. Conserved signals for O-linked glycosylation and receptor-mediated endocytosis. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68574-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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11
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Wojchowski DM, Parsons P, Nordin JH, Kunkel JG. Processing of pro-vitellogenin in insect fat body: a role for high-mannose oligosaccharide. Dev Biol 1986; 116:422-30. [PMID: 3732614 DOI: 10.1016/0012-1606(86)90143-0] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Several discrete events were resolved in the processing of vitellogenin in Blattella germanica. Using tunicamycin to inhibit the synthesis of high-mannose oligosaccharide, a high molecular weight pro-vitellogenin peptide (apo-proVG, Mr 215,000) was identified in fat body. Dosages of tunicamycin which inhibited glycosylation of vitellogenin by 98% inhibited its synthesis by as much as 59%, yet led to an intracellular accumulation of apo-proVG. Reversibility and dose dependency of these effects on vitellogenin synthesis, glycosylation, proteolytic processing, and secretion were demonstrated. In control insects, glycosylation of apo-proVG yielded a Mr 240,000 pro-vitellogenin peptide (proVG). FITC-Concanavalin A bound to purified proVG but not to apo-proVG, thus confirming an absence of high-mannose oligosaccharide in the apo-protein. Following its glycosylation, proVG was processed rapidly in fat body to Mr 160,000 (VG160) and Mr 102,000 (VG102) peptides which subsequently were secreted into hemolymph. After uptake into developing oocytes, the VG160 peptide was processed further prior to chorionation, yielding subunits of Mr 95,000 and 50,000. Uniqueness of the peptides of mature vitellin (Mr 102,000, 95,000, and 50,000) was indicated by comparison of the CNBr fragments of each purified subunit. Staining of CNBr fragments with FITC-Concanavalin A also indicated that high-mannose oligosaccharides are attached at one or more sites within each vitellin subunit. Resolution of the substructure of this insect vitellin and identification of events involved in the processing and secretion of its fat body apo-protein provide a basis for further study of the assembly and transport of vitellogenin, its packaging in eggs, and utilization during embryogenesis.
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Soreq H. The biosynthesis of biologically active proteins in mRNA-microinjected Xenopus oocytes. CRC CRITICAL REVIEWS IN BIOCHEMISTRY 1985; 18:199-238. [PMID: 2412759 DOI: 10.3109/10409238509085134] [Citation(s) in RCA: 94] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The basic properties of mRNA-injected Xenopus oocytes as a heterologous system for the production of biologically active proteins will be reviewed. The advantages and limitations involved in the use of this in ovo system will be discussed, as compared with in vitro cell-free translation systems and with in vivo microinjected mammalian cells in culture. The different assay systems that have been utilized for the identification of the biological properties of oocyte-produced proteins will be described. This section will review the determination of properties such as binding of natural ligands, like heme or alpha-bungarotoxin; immunological recognition by antibodies; subcellular compartmentalization and/or secretion; various enzymatic catalytic activities; and induction in ovo of biological activities that affect other living cells in culture, such as those of interferon and of the T-cell receptor. The limitations involved in interpretation of results obtained using mRNA-injected oocytes will be critically reviewed. Special attention will be given to the effect of oocyte proteases and of changes in the endogenous translation rate on quantitative measurements of oocyte-produced proteins. In addition, the validity of the various measurement techniques will be evaluated. The various uses of bioassays of proteins produced in mRNA-injected Xenopus oocytes throughout the last decade will be reviewed. Nuclear and cytoplasmic injections, mRNA and protein turnover measurements and abundance calculations, and the use of in ovo bioassays for molecular cloning experiments will be discussed in this section. Finally, potential future uses of the oocyte system in various fields of research, such as immunology, neurobiology, and cell biology will be suggested.
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Ronnett GV, Knutson VP, Kohanski RA, Simpson TL, Lane MD. Role of glycosylation in the processing of newly translated insulin proreceptor in 3T3-L1 adipocytes. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)43084-5] [Citation(s) in RCA: 109] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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14
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Viskochil DH, Perry ST, Lea OA, Stafford DW, Wilson EM, French FS. Isolation of two genomic sequences encoding the Mr = 14,000 subunit of rat prostatein. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32135-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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