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Varki A. Biological roles of glycans. Glycobiology 2016; 27:3-49. [PMID: 27558841 PMCID: PMC5884436 DOI: 10.1093/glycob/cww086] [Citation(s) in RCA: 1403] [Impact Index Per Article: 175.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 08/15/2016] [Accepted: 08/16/2016] [Indexed: 02/07/2023] Open
Abstract
Simple and complex carbohydrates (glycans) have long been known to play major metabolic, structural and physical roles in biological systems. Targeted microbial binding to host glycans has also been studied for decades. But such biological roles can only explain some of the remarkable complexity and organismal diversity of glycans in nature. Reviewing the subject about two decades ago, one could find very few clear-cut instances of glycan-recognition-specific biological roles of glycans that were of intrinsic value to the organism expressing them. In striking contrast there is now a profusion of examples, such that this updated review cannot be comprehensive. Instead, a historical overview is presented, broad principles outlined and a few examples cited, representing diverse types of roles, mediated by various glycan classes, in different evolutionary lineages. What remains unchanged is the fact that while all theories regarding biological roles of glycans are supported by compelling evidence, exceptions to each can be found. In retrospect, this is not surprising. Complex and diverse glycans appear to be ubiquitous to all cells in nature, and essential to all life forms. Thus, >3 billion years of evolution consistently generated organisms that use these molecules for many key biological roles, even while sometimes coopting them for minor functions. In this respect, glycans are no different from other major macromolecular building blocks of life (nucleic acids, proteins and lipids), simply more rapidly evolving and complex. It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences.
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Affiliation(s)
- Ajit Varki
- Departments of Medicine and Cellular & Molecular Medicine, Glycobiology Research and Training Center, University of California at San Diego, La Jolla, CA 92093-0687, USA
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2
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Yan Q, Lennarz WJ. Studies on the function of oligosaccharyl transferase subunits. Stt3p is directly involved in the glycosylation process. J Biol Chem 2002; 277:47692-700. [PMID: 12359722 DOI: 10.1074/jbc.m208136200] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the yeast, Saccharomyces cerevisiae, oligosaccharyl transferase (OT) is composed of nine different transmembrane proteins. Using a glycosylatable peptide containing a photoprobe, we previously found that only one essential subunit, Ost1p, was specifically labeled by the photoprobe and recently have shown that it does not contain the recognition domain for the glycosylatable sequence Asn-Xaa-Thr/Ser. In this study we utilized additional glycosylatable peptides containing two photoreactive groups and found that these were linked to Stt3p and Ost3p. Stt3p is the most conserved subunit in the OT complex, and therefore 21 block mutants in the lumenal region were prepared. Of the 14 lethal mutant proteins only two, as well as one temperature-sensitive mutant protein, were incorporated into the OT complex. However, using microsomes prepared from these three strains, the labeling of Ost1p was markedly decreased upon photoactivation with the Asn-Bpa-Thr photoprobe. Based on the block mutants single amino acid mutations were prepared and analyzed. From all of these results, we conclude that the sequence from residues 516 to 520, WWDYG in Stt3p, plays a central role in glycosylatable peptide recognition and/or the catalytic glycosylation process.
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Affiliation(s)
- Qi Yan
- Department of Biochemistry and Cell Biology and the Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, New York 11794-5215, USA
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3
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Abstract
Oligosaccharyltransferase (OST) catalyzes the en bloc transfer of dolichylpyrophosphate oligosaccharides to an asparagine residue found in the sequon Asn-Xaa-Thr/Ser of newly synthesized proteins. Currently the method most commonly used to monitor this reaction, involving multiple solvent extractions and HPLC, is extremely time consuming and tedious. Herein, we present the use of a biotinylated peptide as the acceptor substrate and dolichylpyrophosphate [3H]chitobiose as the donor substrate for the OST-catalyzed reaction. This allows for separation (avidin-agarose beads) and quantitative analysis (scintillation counting) of only the biotinylated glycopeptide product of the OST-catalyzed reaction. This new assay yields highly reproducible results in a rapid manner.
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Affiliation(s)
- Anjali Srinivasan
- Department of Medicinal Chemistry, University of Michigan, Ann Arobr 48109-1055, USA
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4
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Gillece P, Luz JM, Lennarz WJ, de la Cruz FJ, Römisch K. Export of a cysteine-free misfolded secretory protein from the endoplasmic reticulum for degradation requires interaction with protein disulfide isomerase. J Cell Biol 1999; 147:1443-56. [PMID: 10613903 PMCID: PMC2174254 DOI: 10.1083/jcb.147.7.1443] [Citation(s) in RCA: 154] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/1998] [Accepted: 11/18/1999] [Indexed: 12/26/2022] Open
Abstract
Protein disulfide isomerase (PDI) interacts with secretory proteins, irrespective of their thiol content, late during translocation into the ER; thus, PDI may be part of the quality control machinery in the ER. We used yeast pdi1 mutants with deletions in the putative peptide binding region of the molecule to investigate its role in the recognition of misfolded secretory proteins in the ER and their export to the cytosol for degradation. Our pdi1 deletion mutants are deficient in the export of a misfolded cysteine-free secretory protein across the ER membrane to the cytosol for degradation, but ER-to-Golgi complex transport of properly folded secretory proteins is only marginally affected. We demonstrate by chemical cross-linking that PDI specifically interacts with the misfolded secretory protein and that mutant forms of PDI have a lower affinity for this protein. In the ER of the pdi1 mutants, a higher proportion of the misfolded secretory protein remains associated with BiP, and in export-deficient sec61 mutants, the misfolded secretory protein remain bounds to PDI. We conclude that the chaperone PDI is part of the quality control machinery in the ER that recognizes terminally misfolded secretory proteins and targets them to the export channel in the ER membrane.
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Affiliation(s)
- Pauline Gillece
- University of Cambridge, Cambridge Institute for Medical Research, Wellcome Center for the Study of Molecular Mechanisms in Disease, Cambridge CB2 2XY, United Kingdom
| | - José Manuel Luz
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215
| | - William J. Lennarz
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215
| | | | - Karin Römisch
- University of Cambridge, Cambridge Institute for Medical Research, Wellcome Center for the Study of Molecular Mechanisms in Disease, Cambridge CB2 2XY, United Kingdom
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5
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Yan Q, Prestwich GD, Lennarz WJ. The Ost1p subunit of yeast oligosaccharyl transferase recognizes the peptide glycosylation site sequence, -Asn-X-Ser/Thr-. J Biol Chem 1999; 274:5021-5. [PMID: 9988747 DOI: 10.1074/jbc.274.8.5021] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Other laboratories have established that oligosaccharyl transferase (OST) from Saccharomyces cerevisiae can be purified as a protein complex containing eight different subunits. To identify the OST subunit that recognizes the peptide sites that can be glycosylated, we developed photoaffinity probes containing a photoreactive benzophenone derivative, p-benzoylphenylalanine (Bpa), as part of an 125I-labeled peptide that could be expected to be glycosylated. We found that Asn-Bpa-Thr peptides served as substrates for OST and that photoactivation of these probes in the presence of microsomes abolished the OST activity. Photoactivation of 125I-labeled Asn-Bpa-Thr in the presence of microsomes resulted in specific covalent labeling of a protein doublet of molecular mass 62 and 64 kDa. By carrying out the photoactivation of the probe using microsomes containing epitope-tagged Ost1p, we demonstrated that the 125I-labeled protein was Ost1p. Radiolabeling of this protein was dependent on irradiation at 350 nm. No labeling was detected using a probe containing Ala instead of Thr as the third amino acid residue. We conclude that Ost1p is the subunit of the OST complex that recognizes the peptide sites in the nascent chains that are destined to be glycosylated.
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Affiliation(s)
- Q Yan
- Department of Biochemistry and Cell Biology and the Institute for Cell and Developmental Biology, SUNY at Stony Brook, Stony Brook, New York 11794, USA
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6
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Breuer W, Bause E. Oligosaccharyl Transferase is a Constitutive Component of an Oligomeric Protein Complex from Pig Liver Endoplasmic Reticulum. ACTA ACUST UNITED AC 1995. [DOI: 10.1111/j.1432-1033.1995.0689m.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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7
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Purification and characterization of avian oligosaccharyltransferase. Complete amino acid sequence of the 50-kDa subunit. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)36853-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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8
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LaMantia ML, Lennarz WJ. The essential function of yeast protein disulfide isomerase does not reside in its isomerase activity. Cell 1993; 74:899-908. [PMID: 8374956 DOI: 10.1016/0092-8674(93)90469-7] [Citation(s) in RCA: 169] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Protein disulfide isomerase (PDI) is believed to function in vivo by catalyzing the isomerization of disulfide bonds in proteins and thereby facilitating their folding. In S. cerevisiae PDI is encoded by an essential gene. Deletion of nearly one-third of the C-terminal residues of PDI altered PDI's cellular localization but not cell viability. Further deletions resulted in lethality, but these truncated proteins still exhibited PDI activity in vitro. Cells carrying a variant PDI in which both-CGHC-active sites were disrupted were viable. However, these cells exhibited a delay in the disulfide bond formation and transport of carboxypeptidase Y. In vitro enzyme assays revealed that disruption of both sites abolished catalytic activity. These results indicate that PDI catalyzes disulfide bond formation both in vivo and in vitro and that the integrity of the active sites is required for catalysis. However, this catalytic activity is not essential for yeast viability.
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Affiliation(s)
- M L LaMantia
- Department of Biochemistry and Cell Biology, State University of New York at Stony Brook 11794-5215
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9
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Bulleid NJ. Protein disulfide-isomerase: role in biosynthesis of secretory proteins. ADVANCES IN PROTEIN CHEMISTRY 1993; 44:125-50. [PMID: 8317296 DOI: 10.1016/s0065-3233(08)60566-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- N J Bulleid
- Department of Biochemistry and Molecular Biology, University of Manchester, England
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10
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Kelleher DJ, Kreibich G, Gilmore R. Oligosaccharyltransferase activity is associated with a protein complex composed of ribophorins I and II and a 48 kd protein. Cell 1992; 69:55-65. [PMID: 1555242 DOI: 10.1016/0092-8674(92)90118-v] [Citation(s) in RCA: 236] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Oligosaccharyltransferase catalyzes the N-linked glycosylation of asparagine residues on nascent polypeptides in the lumen of the rough endoplasmic reticulum (RER). A protein complex composed of 66, 63, and 48 kd subunits copurified with oligosaccharyltransferase from canine pancreas. The 66 and 63 kd subunits were shown by protein immunoblotting to be identical to ribophorin I and II, two previously identified RER glycoproteins that colocalize with membrane-bound ribosomes. The transmembrane segment of ribophorin I was found to be homologous to a recently proposed dolichol recognition consensus sequence. Based on a revision of the consensus sequence, we propose a model for the interaction of dolichol with the glycosyltransferases that catalyze the assembly and transfer of lipid-linked oligosaccharides.
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Affiliation(s)
- D J Kelleher
- Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester 01655
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11
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Noiva R, Lennarz W. Protein disulfide isomerase. A multifunctional protein resident in the lumen of the endoplasmic reticulum. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)50556-7] [Citation(s) in RCA: 152] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
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12
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Noiva R, Kimura H, Roos J, Lennarz W. Peptide binding by protein disulfide isomerase, a resident protein of the endoplasmic reticulum lumen. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)55041-9] [Citation(s) in RCA: 44] [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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13
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Marchase RB, Burkart MF, Rivera AA, Clarke BL, Shur BD, Overmeyer GT, Shaw DR. beta-Phosphorothioate analogs of nucleotide sugars are resistant to hydrolytic degradation and utilized efficiently by glycosyltransferases. Anal Biochem 1991; 197:40-6. [PMID: 1835319 DOI: 10.1016/0003-2697(91)90352-t] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The alpha- and beta-phosphorothioate analogs of UDP-Gal and UDP-Glc, in which a sulfur is exchanged for a non-bridging oxygen at one of the phosphate groups, have been synthesized and tested for their resistance to enzymatic degradation and for their usefulness in glycosyltransferase reactions. The alpha analogs were found to be no more resistant to hydrolysis than the native nucleotide sugars, but as previously reported (R. B. Marchase et al. (1987) Biochim. Biophys. Acta 916: 157) the beta S analogs were approximately 10 times more resistant. The beta S analog and native UDP-Glc were found to have comparable Km's when used in assays for glucosylphosphoryl dolichol synthase with rat liver and hen oviduct microsomes, although the apparent Vmax of the reaction was about twofold higher for the analog, presumably due to its resistance to degradation. Partially purified 4 beta-galactosyltransferase exhibited a Vmax with (beta S)UDP-Gal that was only slightly lower than that with UDP-Gal and a Km that was slightly increased. The effectiveness of the analog was especially apparent in assays for 4 beta-galactosyltransferase on intact sperm and in rat liver homogenates, in which hydrolysis of the normal substrate was very rapid and net incorporation was at least 4 times greater with the beta S analog in each system.
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Affiliation(s)
- R B Marchase
- Department of Cell Biology, University of Alabama, Birmingham 35294
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14
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Kimura H, Noiva R, Mizunaga T, Yamauchi K, Horiuchi R, Cheng SY, Lennarz WJ. Thyroid hormone binding protein contains glycosylation site binding protein activity. Biochem Biophys Res Commun 1990; 170:1319-24. [PMID: 2202300 DOI: 10.1016/0006-291x(90)90538-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Several lines of evidence provided by other workers indicate that within the same species thyroid hormone binding protein, the beta-subunit of prolyl hydroxylase, and protein disulfide isomerase are the same protein. We sought to determine if glycosylation site binding protein, a lumenal protein of the endoplasmic reticulum, also has the same primary structure. To accomplish this the level of glycosylation site binding protein (GSBP) activity, measured by photolabeling with a glycosylation site peptide probe, was carried out in preparations of 3T3 cells and in E. coli transformed with human thyroid hormone binding protein cDNA. The results strongly support the idea that GSBP is identical to these other lumenal proteins of the endoplasmic reticulum.
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Affiliation(s)
- H Kimura
- Department of Biochemistry and Cell Biology, SUNY at Stony Brook, NY 11794-5215
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15
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Geetha-Habib M, Park H, Lennarz W. In vivo N-glycosylation and fate of Asn-X-Ser/Thr tripeptides. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)77399-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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16
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Freeze HH, Koza-Taylor P, Jones JA, Loomis WF. Cell-free N-glycosylation in Dictyostelium discoideum: analysis of wild-type and mutants defective in lipid-linked oligosaccharide biosynthesis. J Cell Biochem 1990; 43:27-42. [PMID: 2347875 DOI: 10.1002/jcb.240430104] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
N-glycosylation was measured in wild-type cell lysates of Dictyostelium discoideum and in two mutant strains that synthesize a truncated lipid-linked oligosaccharide, Man6GlcNAc2 lacking terminal mannose and glucose residues. Endogenous lipid-linked oligosaccharide (LLO) was transferred to octanoyl-Asn-[125I]Tyr-ThrNH2 by membrane fractions. About 50% of the glycopeptide product remained associated with membranes. Taurocholate and saponin promoted and preserved glycosylation, but NP-40 and Triton X-100 did not. Using this artificial assay, the rate and extent of transfer of the truncated lipid-linked oligosaccharide in extracts of the two mutant strains, HL241 and HL243, was reduced 5-10-fold relative to that of wild-type. The low activity found in the mutant strains appears to result from either reduced affinity of the truncated LLO for the transferase or from its improper topological localization in the membrane. When protein N-glycosylation is measured in living cells it is nearly normal in HL241, but it is 3-4-fold decreased in HL243. Although the results of the in vitro and in vivo assays differ, they are not in conflict. Rather, they suggest that the static in vitro assay may be capable of revealing subtleties in the productive positioning of LLO and the oligosaccharyl transferase. The decrease in glycosylation seen in intact HL243 cells may be a consequence of the pleiotropic effects of the primary mutation rather than a direct result of the altered LLO structure. Genetic analysis showed that the mutation in HL241 is recessive, while the mutation in HL243 is dominant and prevents normal development. Thus, the two mutants share a lesion in lipid-linked oligosaccharide biosynthesis and in cell-free glycosylation, but differ in their in vivo glycosylation. Their primary defects are probably different.
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Affiliation(s)
- H H Freeze
- Department of Medicine, University of California, San Diego, La Jolla 92093
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17
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Lipid-linked Saccharides in Plants: Intermediates in the Synthesis of N-linked Glycoproteins. ACTA ACUST UNITED AC 1990. [DOI: 10.1016/b978-0-12-461012-5.50009-4] [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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18
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Clarke BL, Naylor C, Lennarz WJ. Comparative studies on mannosylphosphoryl dolichol and glucosylphosphoryl dolichol synthases. Chem Phys Lipids 1989; 51:239-47. [PMID: 2532983 DOI: 10.1016/0009-3084(89)90011-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Factors affecting the synthesis of mannosylphosphoryl dolichol and glucosylphosphoryl dolichol hen oviduct microsomes were compared in order to gain insight into the properties of their respective synthases. A stabilized form of mannosylphosphoryl dolichol synthase, but not glucosylphosphoryl dolichol synthase, was released from microsomes by freezing the membranes after exposure to the detergent CHAPSO. The activation energy for mannosylphosphoryl dolichol synthesis in membranes was 9.4 glucosylphosphoryl dolichol synthesis in membranes had a similar activation energy, 8.1 kcal/mol, but below 18 degrees C the value was 16.7 kcal/mol. Tryptic digestion of sealed microsomes preferentially inactivated mannosylphosphoryl dolichol synthase; however, both synthases were equally inactivated in detergent-permeabilized microsomes. Periodate-oxidized UDP-Glc was used to probe the topological orientation of glucosylphosphoryl dolichol synthase in rat liver microsomes. Sealed microsomes treated with oxidized UDP-Glc were inactive in synthesis of glucosylphosphoryl dolichol. However, when these treated microsomes were permeabilized, glucosylphosphoryl dolichol synthase activity was readily detected. From these studies we conclude that although mannosyl- and glucosylphosphoryl dolichol synthases catalyze chemically similar reactions in the endoplasmic reticulum, they differ in several respects. These differences were interpreted in terms of a topological model in which the active sites of the two enzymes reside on opposite faces of the endoplasmic reticulum, with that of the glucosyl lipid synthase facing the lumen and that of the mannosyl lipid synthase facing the cytosol.
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Affiliation(s)
- B L Clarke
- Department of Physiology and Biophysics, University of Alabama, Birmingham 35294
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19
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Chalifour RJ, Spiro RG. Effect of phospholipids on thyroid oligosaccharyltransferase activity and orientation. Evaluation of structural determinants for stimulation of N-glycosylation. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)37640-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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20
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Geetha-Habib M, Noiva R, Kaplan HA, Lennarz WJ. Glycosylation site binding protein, a component of oligosaccharyl transferase, is highly similar to three other 57 kd luminal proteins of the ER. Cell 1988; 54:1053-60. [PMID: 2458190 DOI: 10.1016/0092-8674(88)90120-1] [Citation(s) in RCA: 134] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A 57 kd component of oligosaccharyl transferase, termed glycosylation site binding protein, specifically recognizes a photoaffinity probe containing the N-glycosylation site sequence Asn-Lys-Thr. It is present in the lumen of the ER (endoplasmic reticulum) and its release from this compartment results in a loss of N-glycosylation. Antibodies against this protein were used to identify cDNA clones from a lambda gt11 expression library. Analysis of its cDNA sequence reveals high sequence similarity to three other 57 kd luminal endoplasmic reticulum proteins: protein disulfide isomerase, the beta-subunit of prolyl hydroxylase, and thyroid hormone binding protein. This finding suggests that the capacity to recognize multiple polypeptide domains may reside in a single luminal protein that participates in co- and/or posttranslational modifications of newly synthesized proteins.
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Affiliation(s)
- M Geetha-Habib
- Department of Biochemistry and Molecular Biology, University of Texas MD Anderson Cancer Center, Houston 77030
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21
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Kaplan HA, Naider F, Lennarz WJ. Partial characterization and purification of the glycosylation site recognition component of oligosaccharyltransferase. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68571-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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Kaplan HA, Welply JK, Lennarz WJ. Oligosaccharyl transferase: the central enzyme in the pathway of glycoprotein assembly. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 906:161-73. [PMID: 3297152 DOI: 10.1016/0304-4157(87)90010-4] [Citation(s) in RCA: 128] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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23
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Grant SR, Welply JK, Olson EN, Lennarz WJ. Oligosaccharyltransferase activity is markedly increased during differentiation of a nonfusing myoblast cell line. Arch Biochem Biophys 1986; 248:424-8. [PMID: 3729427 DOI: 10.1016/0003-9861(86)90439-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
We have studied several aspects of glycoprotein synthesis in myoblast differentiation by using a nonfusing myoblast cell line, BC3H1. Previous studies showed that transfer of proliferating undifferentiated BC3H1 cells to mitogen-depleted medium results in the cells' withdrawal from the cell cycle and induction of a variety of muscle-specific gene products [E. N. Olson, L. Glaser, J. P. Merlie, R. Sebane, and J. Lindstrom (1983) J. Biol. Chem. 258, 13946-13953]. Because cell surface glycoproteins have been implicated in myoblast differentiation, in the present study we measured the amount of oligosaccharyltransferase in microsomes isolated from BC3H1 cells at various stages of differentiation. By using an acceptor peptide containing the sequence-Asn-Leu-Thr-, enzyme activity was measured by formation of [3H]glycopeptide. In addition, active enzyme protein was measured with a 125I-labeled photoreactive derivative of the acceptor tripeptide. Both of these independent assay methods revealed a marked increase in oligosaccharyltransferase when differentiation was induced by serum depletion. Moreover, mitogenic stimulation of differentiated cells resulted in a return of oligosaccharyltransferase to near basal levels. This reversible increase in this key enzyme in protein glycosylation occurred despite the fact that both total protein and glycoprotein synthesis were depressed during differentiation. These data indicate that during myogenesis the level of oligosaccharyltransferase is regulated in parallel with a number of muscle-specific gene products. These results are discussed in the context of regulation of the pathway of glycoprotein synthesis.
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24
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Welply JK, Kaplan HA, Shenbagamurthi P, Naider F, Lennarz WJ. Studies on properties of membrane-associated oligosaccharyltransferase using an active site-directed photoaffinity probe. Arch Biochem Biophys 1986; 246:808-19. [PMID: 3707133 DOI: 10.1016/0003-9861(86)90337-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Previous attempts in several laboratories, including ours, to purify oligosaccharyl-transferase have met with limited success because of the lability of the membrane-associated enzyme after solubilization with detergents. In an effort to identify the enzyme in face of this lability, we recently developed a photoaffinity reagent to label the active site [J. K. Welply, P. Shenbagamurthi, F. Naider, H. R. Park, and W. J. Lennarz (1985) J. Biol. Chem. 260, 6459-6465]. In this report, the preparations of a more sensitive selective labeling probe, 125I-labeled N alpha-3-(4-hydroxyphenylpropionyl)-Asn-Lys-(N epsilon-p-azidobenzoyl)-Thr-NH2, is described. Using this new probe, we have confirmed, independently of catalytic activity, that hen oviduct oligosaccharyltransferase is tightly associated with the endoplasmic reticulum membrane. The 125I-labeled oligosaccharyltransferase was released from the membrane by detergent and strong alkali treatments but not by sonication, high salt, or hypotonic shock. However, all procedures that released the enzyme from the membrane resulted in a dramatic loss of enzyme activity. Treatment of sealed microsomal membrane vesicles with phospholipase A resulted in nearly complete enzyme inactivation; in contrast, phospholipase C or D had moderate or little effect, respectively. Taken together, these results suggest that the hydrophobic environment of the membrane is required for oligosaccharyltransferase activity. Trypsin treatment of intact vesicles diminished enzyme activity by nearly 70%, but it had no effect on the binding affinity of the enzyme for the 125I-labeled photoaffinity probe. This result suggests that the polypeptide acceptor portion of oligosaccharyltransferase is lumenally disposed, and that a trypsin-sensitive, cytoplasmically oriented domain or another subunit binds the carbohydrate donor, dolichol-PP-oligosaccharide.
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