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De Masi R, Orlando S. GANAB and N-Glycans Substrates Are Relevant in Human Physiology, Polycystic Pathology and Multiple Sclerosis: A Review. Int J Mol Sci 2022; 23:7373. [PMID: 35806376 PMCID: PMC9266668 DOI: 10.3390/ijms23137373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Revised: 06/22/2022] [Accepted: 06/28/2022] [Indexed: 11/29/2022] Open
Abstract
Glycans are one of the four fundamental macromolecular components of living matter, and they are highly regulated in the cell. Their functions are metabolic, structural and modulatory. In particular, ER resident N-glycans participate with the Glc3Man9GlcNAc2 highly conserved sequence, in protein folding process, where the physiological balance between glycosylation/deglycosylation on the innermost glucose residue takes place, according GANAB/UGGT concentration ratio. However, under abnormal conditions, the cell adapts to the glucose availability by adopting an aerobic or anaerobic regimen of glycolysis, or to external stimuli through internal or external recognition patterns, so it responds to pathogenic noxa with unfolded protein response (UPR). UPR can affect Multiple Sclerosis (MS) and several neurological and metabolic diseases via the BiP stress sensor, resulting in ATF6, PERK and IRE1 activation. Furthermore, the abnormal GANAB expression has been observed in MS, systemic lupus erythematous, male germinal epithelium and predisposed highly replicating cells of the kidney tubules and bile ducts. The latter is the case of Polycystic Liver Disease (PCLD) and Polycystic Kidney Disease (PCKD), where genetically induced GANAB loss affects polycystin-1 (PC1) and polycystin-2 (PC2), resulting in altered protein quality control and cyst formation phenomenon. Our topics resume the role of glycans in cell physiology, highlighting the N-glycans one, as a substrate of GANAB, which is an emerging key molecule in MS and other human pathologies.
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Affiliation(s)
- Roberto De Masi
- Complex Operative Unit of Neurology, “F. Ferrari” Hospital, Casarano, 73042 Lecce, Italy;
- Laboratory of Neuroproteomics, Multiple Sclerosis Centre, “F. Ferrari” Hospital, Casarano, 73042 Lecce, Italy
| | - Stefania Orlando
- Laboratory of Neuroproteomics, Multiple Sclerosis Centre, “F. Ferrari” Hospital, Casarano, 73042 Lecce, Italy
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Abstract
N-glycosylation is a highly conserved glycan modification, and more than 7000 proteins are N-glycosylated in humans. N-glycosylation has many biological functions such as protein folding, trafficking, and signal transduction. Thus, glycan modification to proteins is profoundly involved in numerous physiological and pathological processes. The N-glycan precursor is biosynthesized in the endoplasmic reticulum (ER) from dolichol phosphate by sequential enzymatic reactions to generate the dolichol-linked oligosaccharide composed of 14 sugar residues, Glc3Man9GlcNAc2. The oligosaccharide is then en bloc transferred to the consensus sequence N-X-S/T (X represents any amino acid except proline) of nascent proteins. Subsequently, the N-glycosylated nascent proteins enter the folding step, in which N-glycans contribute largely to attaining the correct protein fold by recruiting the lectin-like chaperones, calnexin, and calreticulin. Despite the N-glycan-dependent folding process, some glycoproteins do not fold correctly, and these misfolded glycoproteins are destined to degradation by proteasomes in the cytosol. Properly folded proteins are transported to the Golgi, and N-glycans undergo maturation by the sequential reactions of glycosidases and glycosyltransferases, generating complex-type N-glycans. N-Acetylglucosaminyltransferases (GnT-III, GnT-IV, and GnT-V) produce branched N-glycan structures, affording a higher complexity to N-glycans. In this chapter, we provide an overview of the biosynthetic pathway of N-glycans in the ER and Golgi.
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Quality control of glycoprotein folding and ERAD: the role of N-glycan handling, EDEM1 and OS-9. Histochem Cell Biol 2016; 147:269-284. [DOI: 10.1007/s00418-016-1513-9] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/20/2016] [Indexed: 02/03/2023]
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4
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Caputo AT, Alonzi DS, Marti L, Reca IB, Kiappes JL, Struwe WB, Cross A, Basu S, Lowe ED, Darlot B, Santino A, Roversi P, Zitzmann N. Structures of mammalian ER α-glucosidase II capture the binding modes of broad-spectrum iminosugar antivirals. Proc Natl Acad Sci U S A 2016; 113:E4630-8. [PMID: 27462106 PMCID: PMC4987793 DOI: 10.1073/pnas.1604463113] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The biosynthesis of enveloped viruses depends heavily on the host cell endoplasmic reticulum (ER) glycoprotein quality control (QC) machinery. This dependency exceeds the dependency of host glycoproteins, offering a window for the targeting of ERQC for the development of broad-spectrum antivirals. We determined small-angle X-ray scattering (SAXS) and crystal structures of the main ERQC enzyme, ER α-glucosidase II (α-GluII; from mouse), alone and in complex with key ligands of its catalytic cycle and antiviral iminosugars, including two that are in clinical trials for the treatment of dengue fever. The SAXS data capture the enzyme's quaternary structure and suggest a conformational rearrangement is needed for the simultaneous binding of a monoglucosylated glycan to both subunits. The X-ray structures with key catalytic cycle intermediates highlight that an insertion between the +1 and +2 subsites contributes to the enzyme's activity and substrate specificity, and reveal that the presence of d-mannose at the +1 subsite renders the acid catalyst less efficient during the cleavage of the monoglucosylated substrate. The complexes with iminosugar antivirals suggest that inhibitors targeting a conserved ring of aromatic residues between the α-GluII +1 and +2 subsites would have increased potency and selectivity, thus providing a template for further rational drug design.
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Affiliation(s)
- Alessandro T Caputo
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Dominic S Alonzi
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Lucia Marti
- Institute of Sciences of Food Production, Consiglio Nazionale delle Ricerche Unit of Lecce, 73100 Lecce, Italy
| | - Ida-Barbara Reca
- Institute of Sciences of Food Production, Consiglio Nazionale delle Ricerche Unit of Lecce, 73100 Lecce, Italy
| | - J L Kiappes
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Weston B Struwe
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Alice Cross
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Souradeep Basu
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Edward D Lowe
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Benoit Darlot
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom; Ecole Nationale Supérieure de Chimie de Montpellier, 34296 Montpellier Cedex 5, France
| | - Angelo Santino
- Institute of Sciences of Food Production, Consiglio Nazionale delle Ricerche Unit of Lecce, 73100 Lecce, Italy
| | - Pietro Roversi
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom;
| | - Nicole Zitzmann
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom;
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5
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Synthesis and α-Glucosidase II inhibitory activity of valienamine pseudodisaccharides relevant to N-glycan biosynthesis. Bioorg Med Chem Lett 2011; 21:5219-23. [DOI: 10.1016/j.bmcl.2011.07.046] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2011] [Revised: 07/11/2011] [Accepted: 07/12/2011] [Indexed: 11/18/2022]
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Miyagawa A, Totani K, Matsuo I, Ito Y. Promiscuous activity of ER glucosidase II discovered through donor specificity analysis of UGGT. Biochem Biophys Res Commun 2010; 403:322-8. [PMID: 21075077 DOI: 10.1016/j.bbrc.2010.11.027] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2010] [Accepted: 11/08/2010] [Indexed: 10/18/2022]
Abstract
In glycoprotein quality control system in the endoplasmic reticulum (ER), UGGT (UDP-glucose:glycoprotein glucosyltransferase) and glucosidase II (G-II) play key roles. UGGT serves as a glycoprotein folding sensor by virtue of its unique specificity to glucosylate glycoproteins at incompletely folded stage. By using various UDP-Glc analogues, we first analyzed donor specificity of UGGT, which was proven to be rather narrow. However, marginal activity was observed with UDP-galactose and UDP-glucuronic acid as well as with 3-, 4- and 6-deoxy glucose analogues to give corresponding transfer products. Intriguingly, G-II smoothly converted all of them back to Man(9)GlcNAc(2), providing an indication that G-II has a promiscuous activity as a broad specificity hexosidase.
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Affiliation(s)
- Atsushi Miyagawa
- RIKEN Advanced Science Institute, Wako, Saitama 351-0198, Japan.
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Takeda Y, Totani K, Matsuo I, Ito Y. The action of bromoconduritol on ER glucosidase II. Bioorg Med Chem Lett 2010; 20:5357-9. [DOI: 10.1016/j.bmcl.2009.05.125] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2009] [Revised: 05/29/2009] [Accepted: 05/30/2009] [Indexed: 11/26/2022]
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D'Alessio C, Caramelo JJ, Parodi AJ. UDP-GlC:glycoprotein glucosyltransferase-glucosidase II, the ying-yang of the ER quality control. Semin Cell Dev Biol 2010; 21:491-9. [PMID: 20045480 DOI: 10.1016/j.semcdb.2009.12.014] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2009] [Accepted: 12/17/2009] [Indexed: 12/22/2022]
Abstract
The N-glycan-dependent quality control of glycoprotein folding prevents endoplasmic to Golgi exit of folding intermediates, irreparably misfolded glycoproteins and incompletely assembled multimeric complexes. It also enhances folding efficiency by preventing aggregation and facilitating formation of proper disulfide bonds. The control mechanism essentially involves four components, resident lectin-chaperones that recognize monoglucosylated polymannose glycans, a lectin-associated oxidoreductase acting on monoglucosylated glycoproteins, a glucosyltransferase that creates monoglucosytlated epitopes in protein-linked glycans and a glucosidase that removes the glucose units added by the glucosyltransferase. This last enzyme is the only mechanism component sensing glycoprotein conformations as it creates monoglucosylated glycans exclusively in not properly folded species or in not completely assembled complexes. The glucosidase is a dimeric heterodimer composed of a catalytic subunit and an additional one that is partially responsible for the ER localization of the enzyme and for the enhancement of the deglucosylation rate as its mannose 6-phosphate receptor homologous domain presents the substrate to the catalytic site. This review deals with our present knowledge on the glucosyltransferase and the glucosidase.
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Affiliation(s)
- Cecilia D'Alessio
- Laboratory of Glycobiology, Fundación Instituto Leloir, Avda. Patricias Argentinas 435, C1405BWE, Buenos Aires, Argentina
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9
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Takeda Y, Totani K, Matsuo I, Ito Y. Chemical approaches toward understanding glycan-mediated protein quality control. Curr Opin Chem Biol 2009; 13:582-91. [DOI: 10.1016/j.cbpa.2009.09.011] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2009] [Revised: 09/01/2009] [Accepted: 09/05/2009] [Indexed: 10/20/2022]
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10
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Pearse BR, Hebert DN. Lectin chaperones help direct the maturation of glycoproteins in the endoplasmic reticulum. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1803:684-93. [PMID: 19891995 DOI: 10.1016/j.bbamcr.2009.10.008] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Revised: 10/09/2009] [Accepted: 10/20/2009] [Indexed: 02/06/2023]
Abstract
Eukaryotic secretory pathway cargo fold to their native structures within the confines of the endoplasmic reticulum (ER). To ensure a high degree of folding fidelity, a multitude of covalent and noncovalent constraints are imparted upon nascent proteins. These constraints come in the form of topological restrictions or membrane tethers, covalent modifications, and interactions with a series of molecular chaperones. N-linked glycosylation provides inherent benefits to proper folding and creates a platform for interactions with specific chaperones and Cys modifying enzymes. Recent insights into this timeline of protein maturation have revealed mechanisms for protein glycosylation and iterative targeting of incomplete folding intermediates, which provides nurturing interactions with molecular chaperones that assist in the efficient maturation of proteins in the eukaryotic secretory pathway.
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Affiliation(s)
- Bradley R Pearse
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA
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Quinn RP, Mahoney SJ, Wilkinson BM, Thornton DJ, Stirling CJ. A novel role for Gtb1p in glucose trimming of N-linked glycans. Glycobiology 2009; 19:1408-16. [PMID: 19542522 DOI: 10.1093/glycob/cwp087] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Glucosidase II (GluII) is a glycan-trimming enzyme active on nascent glycoproteins in the endoplasmic reticulum (ER). It trims the middle and innermost glucose residues (Glc2 and Glc1) from N-linked glycans. The monoglucosylated glycan produced by the first GluII trimming reaction is recognized by calnexin/calreticulin and serves as the signal for entry into this folding pathway. GluII is a heterodimer of alpha and beta subunits corresponding to yeast Gls2p and Gtb1p, respectively. While Gls2p contains the glucosyl hydrolase active site, the Gtb1p subunit has previously been shown to be essential for the Glc1 trimming event. Here we demonstrate that Gtb1p also determines the rate of Glc2 trimming. In order to further dissect these activities we mutagenized a number of conserved residues across the protein. Our data demonstrate that both the MRH and G2B domains of Gtb1p contribute to the Glc2 trimming event but that the MRH domain is essential for Glc1 trimming.
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Affiliation(s)
- Robert P Quinn
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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12
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Bosis E, Nachliel E, Cohen T, Takeda Y, Ito Y, Bar-Nun S, Gutman M. Endoplasmic reticulum glucosidase II is inhibited by its end products. Biochemistry 2008; 47:10970-80. [PMID: 18803404 DOI: 10.1021/bi801545d] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The calnexin/calreticulin cycle is a quality control system responsible for promoting the folding of newly synthesized glycoproteins entering the endoplasmic reticulum (ER). The association of calnexin and calreticulin with the glycoproteins is regulated by ER glucosidase II, which hydrolyzes Glc 2Man X GlcNAc 2 glycans to Glc 1Man X GlcNAc 2 and further to Glc 0Man X GlcNAc 2 ( X represents any number between 5 and 9). To gain new insights into the reaction mechanism of glucosidase II, we developed a kinetic model that describes the interactions between glucosidase II, calnexin/calreticulin, and the glycans. Our model accurately reconstructed the hydrolysis of glycans with nine mannose residues and glycans with seven mannose residues, as measured by Totani et al. [Totani, K., Ihara, Y., Matsuo, I., and Ito, Y. (2006) J. Biol. Chem. 281, 31502-31508]. Intriguingly, our model predicted that glucosidase II was inhibited by its nonglucosylated end products, where the inhibitory effect of Glc 0Man 7GlcNAc 2 was much stronger than that of Glc 0Man 9GlcNAc 2. These predictions were confirmed experimentally. Moreover, our model suggested that glycans with a different number of mannose residues can be equivalent substrates of glucosidase II, in contrast to what had been previously thought. We discuss the possibility that nonglucosylated glycans, existing in the ER, might regulate the entry of newly synthesized glycoproteins into the calnexin/calreticulin cycle. Our model also shows that glucosidase II does not interact with monoglucosylated glycans while they are bound to calnexin or calreticulin.
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Affiliation(s)
- Eran Bosis
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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13
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Geysens S, Pakula T, Uusitalo J, Dewerte I, Penttilä M, Contreras R. Cloning and characterization of the glucosidase II alpha subunit gene of Trichoderma reesei: a frameshift mutation results in the aberrant glycosylation profile of the hypercellulolytic strain Rut-C30. Appl Environ Microbiol 2005; 71:2910-24. [PMID: 15932985 PMCID: PMC1151825 DOI: 10.1128/aem.71.6.2910-2924.2005] [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: 01/01/2023] Open
Abstract
We describe isolation and characterization of the gene encoding the glucosidase II alpha subunit (GIIalpha) of the industrially important fungus Trichoderma reesei. This subunit is the catalytic part of the glucosidase II heterodimeric enzyme involved in the structural modification within the endoplasmic reticulum (ER) of N-linked oligosaccharides present on glycoproteins. The gene encoding GIIalpha (gls2alpha) in the hypercellulolytic strain Rut-C30 contains a frameshift mutation resulting in a truncated gene product. Based on the peculiar monoglucosylated N-glycan pattern on proteins produced by the strain, we concluded that the truncated protein can still hydrolyze the first alpha-1,3-linked glucose residue but not the innermost alpha-1,3-linked glucose residue from the Glc2Man9GlcNAc2 N-glycan ER structure. Transformation of the Rut-C30 strain with a repaired T. reesei gls2alpha gene changed the glycosylation profile significantly, decreasing the amount of monoglucosylated structures and increasing the amount of high-mannose N-glycans. Full conversion to high-mannose carbohydrates was not obtained, and this was probably due to competition between the endogenous mutant subunit and the introduced wild-type GIIalpha protein. Since glucosidase II is also involved in the ER quality control of nascent polypeptide chains, its transcriptional regulation was studied in a strain producing recombinant tissue plasminogen activator (tPA) and in cultures treated with the stress agents dithiothreitol (DTT) and brefeldin A (BFA), which are known to block protein transport and to induce the unfolded protein response. While the mRNA levels were clearly upregulated upon tPA production or BFA treatment, no such enhancement was observed after DTT addition.
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Affiliation(s)
- Steven Geysens
- Fundamental and Applied Molecular Biology, Department for Molecular Biomedical Research, Ghent University and VIB (Flemish Interuniversity Institute for Biotechnology), Ghent-Zwijnaarde, Belgium
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14
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Cumpstey I, Butters TD, Tennant-Eyles RJ, Fairbanks AJ, France RR, Wormald MR. Synthesis of fluorescence-labelled disaccharide substrates of glucosidase II. Carbohydr Res 2004; 338:1937-49. [PMID: 14499570 DOI: 10.1016/s0008-6215(03)00255-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The fluorescence-labelled disaccharides Glcalpha(1-->3)GlcalphaOR and Glcalpha(1-->3)ManalphaOR, both substrates for the glycoprotein-processing enzyme glucosidase II, were synthesised via the use of a n-pentenyl-derived linker at the anomeric position. This allowed incorporation of a pyrenebutyric acid label, via a sequence of oxidative hydroboration, mesylation, azide displacement, reduction with concomitant global deprotection, and peptide coupling. Selective activation of a fully armed thioglycoside in the presence of n-pentenyl glycosides was readily achieved by the use of methyl triflate as promoter.
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Affiliation(s)
- Ian Cumpstey
- Dyson Perrins Laboratory, Oxford University, South Parks Road, Oxford OX1 3QY, UK
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Roth J, Ziak M, Zuber C. The role of glucosidase II and endomannosidase in glucose trimming of asparagine-linked oligosaccharides. Biochimie 2003; 85:287-94. [PMID: 12770767 DOI: 10.1016/s0300-9084(03)00049-x] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
This review covers various aspects of glucose trimming reactions occurring on asparagine-linked oligosaccharides. Structural and functional features of two enzymes, glucosidase II and endo-alpha-mannosidase, prominently involved in this process are summarized and their striking differences in terms of substrate specificities are highlighted. Recent results of analyses by immunoelectron microscopy of their distribution pattern are presented which demonstrate that glucose trimming is not restricted to the endoplasmic reticulum (ER) but additionally is a function accommodated by the Golgi apparatus. The mutually exclusive subcellular distribution of glucosidase II and endomannosidase are discussed in terms of their significance for quality control of protein folding and N-glycosylation.
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Affiliation(s)
- Jürgen Roth
- Division of Cell and Molecular Pathology, Department of Pathology, University of Zurich, Switzerland.
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16
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Spiro RG. Glucose residues as key determinants in the biosynthesis and quality control of glycoproteins with N-linked oligosaccharides. J Biol Chem 2000; 275:35657-60. [PMID: 11007802 DOI: 10.1074/jbc.r000022200] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- R G Spiro
- Departments of Biological Chemistry and Medicine, Harvard Medical School and Joslin Diabetes Center, Boston, Massachusetts 02215, USA.
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17
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Petrescu AJ, Butters TD, Reinkensmeier G, Petrescu S, Platt FM, Dwek RA, Wormald MR. The solution NMR structure of glucosylated N-glycans involved in the early stages of glycoprotein biosynthesis and folding. EMBO J 1997; 16:4302-10. [PMID: 9250674 PMCID: PMC1170056 DOI: 10.1093/emboj/16.14.4302] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Glucosylated oligomannose N-linked oligosaccharides (Glc(x)Man9GlcNAc2 where x = 1-3) are not normally found on mature glycoproteins but are involved in the early stages of glycoprotein biosynthesis and folding as (i) recognition elements during protein N-glycosylation and chaperone recognition and (ii) substrates in the initial steps of N-glycan processing. By inhibiting the first steps of glycan processing in CHO cells using the alpha-glucosidase inhibitor N-butyl-deoxynojirimycin, we have produced sufficient Glc3Man7GlcNAc2 for structural analysis by nuclear magnetic resonance (NMR) spectroscopy. Our results show the glucosyl cap to have a single, well-defined conformation independent of the rest of the saccharide. Comparison with the conformation of Man9GlcNAc2, previously determined by NMR and molecular dynamics, shows the mannose residues to be largely unaffected by the presence of the glucosyl cap. Sequential enzymatic cleavage of the glucose residues does not affect the conformation of the remaining saccharide. Modelling of the Glc3Man9GlcNAc2, Glc2Man9GlcNAc2 and Glc1Man9GlcNAc2 conformations shows the glucose residues to be fully accessible for recognition. A more detailed analysis of the conformations allows potential recognition epitopes on the glycans to be identified and can form the basis for understanding the specificity of the glucosidases and chaperones (such as calnexin) that recognize these glycans, with implications for their mechanisms of action.
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Affiliation(s)
- A J Petrescu
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, UK
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Chapter 5 Biosynthesis 2b. From Glc3Man9GlcNAc2-protein to Man5GlcNAc2-protein: transfer ‘en bloc’ and processing. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s0167-7306(08)60591-8] [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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19
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Alonso JM, Santa-Cecilia A, Chinchetru MA, Calvo P. Characterization of the maltase activity of glucosidase II from rat liver. Kinetic model. BIOLOGICAL CHEMISTRY HOPPE-SEYLER 1993; 374:977-82. [PMID: 8297500 DOI: 10.1515/bchm3.1993.374.7-12.977] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Glucosidase II is a key enzyme in the processing of N-glycoproteins since it removes the two glucose residues from the protein-linked oligosaccharide Glc2Man9GlcNAc2-R. We have studied the kinetics of the purified enzyme, using maltose as substrate. Analysis of data fitting to single and double-hyperbolic equations and the Eadie-Hofstee profile indicate that the enzyme has two binding (active) sites for the hydrolysis of maltose. The Km and Vmax values for the high-affinity site were 0.43 mM and 691 mU/mg, respectively, whereas the values for the low-affinity site were 57.7 mM and 2888 mU/mg, respectively. The Vmax/Km ratios were 1607 and 50.1 ml/min per g for the high- and low-affinity sites, respectively. A new kinetic model for this enzyme is proposed from the equilibria corresponding to the partial competitive inhibition produced by maltose on p-nitrophenyl-glucosidase activity. The amino acid composition of the enzyme has been established.
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Affiliation(s)
- J M Alonso
- Departamento de Bioquímica y Biología Molecular, Universidad de León, Spain
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Alonso JM, Santa-Cecilia A, Calvo P. Effect of bromoconduritol on glucosidase II from rat liver. A new kinetic model for the binding and hydrolysis of the substrate. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 215:37-42. [PMID: 8344283 DOI: 10.1111/j.1432-1033.1993.tb18004.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Bromoconduritol inhibits the p-nitrophenyl-glucosidase and maltase activities of glucosidase II purified from rat liver, an enzyme that removes the two alpha-1,3-linked glucose residues of the protein-bound oligosaccharide Glc2Man9GlcNAc2 in the processing of N-glycoproteins. The inactivation process exhibits pseudo-first-order kinetics. Previously, we have demonstrated the occurrence of two binding (active) sites in the glucosidase II for the substrates p-nitrophenyl alpha-D-glucopyranoside (pNphGlc) and maltose (high- and low-affinity sites). The inhibition kinetic studies with bromoconduritol indicate that the high- and low-affinity sites for pNphGlc correspond to high- and low-affinity sites for maltose, respectively. Bromoconduritol has no effect on the binding of the substrates (pNphGlc and maltose) to the high-affinity site, although it does modify the low-affinity site and hinders the binding of the two indicated substrates to this site. These results, together with previous reports, have prompted us to propose a new kinetic model of binding and hydrolysis of the physiological substrate of the enzyme, in which the outermost glucose residue would bind and be released at the high-affinity site, whereas the innermost glucose residue would do so at the low-affinity site.
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Affiliation(s)
- J M Alonso
- Departamento de Bioquímica y Biología Molecular, Universidad de León, Spain
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