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Structure of the oligosaccharyl transferase complex at 12 A resolution. Structure 2008; 16:432-40. [PMID: 18334218 DOI: 10.1016/j.str.2007.12.013] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2007] [Revised: 11/30/2007] [Accepted: 12/12/2007] [Indexed: 11/23/2022]
Abstract
Oligosaccharyl transferase (OT) catalyzes the transfer of a lipid-linked oligosaccharide to the nascent polypeptide emerging from the translocon. Currently, there is no structural information on the membrane-embedded OT complex, which consists of eight different polypeptide chains. We report a 12 A resolution cryo-electron microscopy structure of OT from yeast. We mapped the locations of four essential OT subunits through a maltose-binding protein fusion strategy. OT was found to have a large domain in the lumenal side of endoplasmic reticulum where the catalysis occurs. The lumenal domain mainly comprises the catalytic Stt3p, the donor substrate-recognizing Wbp1p, and the acceptor substrate-recognizing Ost1p. A prominent groove was observed between these subunits, and we propose that the nascent polypeptide from the translocon threads through this groove while being scanned by the Ost1p subunit for the presence of the glycosylation sequon.
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2
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Chavan M, Chen Z, Li G, Schindelin H, Lennarz WJ, Li H. Dimeric organization of the yeast oligosaccharyl transferase complex. Proc Natl Acad Sci U S A 2006; 103:8947-52. [PMID: 16754853 PMCID: PMC1482546 DOI: 10.1073/pnas.0603262103] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The enzyme complex oligosaccharyl transferase (OT) catalyzes N-glycosylation in the lumen of the endoplasmic reticulum. The yeast OT complex is composed of nine subunits, all of which are transmembrane proteins. Several lines of evidence, including our previous split-ubiquitin studies, have suggested an oligomeric organization of the OT complex, but the exact oligomeric nature has been unclear. By FLAG epitope tagging the Ost4p subunit of the OT complex, we purified the OT enzyme complex by using the nondenaturing detergent digitonin and a one-step immunoaffinity technique. The digitonin-solubilized OT complex was catalytically active, and all nine subunits were present in the enzyme complex. The purified OT complex had an apparent mass of approximately 500 kDa, suggesting a dimeric configuration, which was confirmed by biochemical studies. EM showed homogenous individual particles and revealed a dimeric structure of the OT complexes that was consistent with our biochemical studies. A 3D structure of the dimeric OT complex at 25-A resolution was reconstructed from EM images. We suggest that the dimeric structure of OT might be required for effective association with the translocon dimer and for its allosteric regulation during cotranslational glycosylation.
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Affiliation(s)
- Manasi Chavan
- *Department of Biochemistry and Cell Biology and Institute for Cell and Developmental Biology, Stony Brook University, Stony Brook, NY 11794
| | - Zhiqiang Chen
- Rudolf Virchow Center for Experimental Biomedicine and Institute of Structural Biology, University of Würzburg, 97078 Würzburg, Germany
| | - Guangtao Li
- *Department of Biochemistry and Cell Biology and Institute for Cell and Developmental Biology, Stony Brook University, Stony Brook, NY 11794
| | - Hermann Schindelin
- *Department of Biochemistry and Cell Biology and Institute for Cell and Developmental Biology, Stony Brook University, Stony Brook, NY 11794
- Rudolf Virchow Center for Experimental Biomedicine and Institute of Structural Biology, University of Würzburg, 97078 Würzburg, Germany
| | - William J. Lennarz
- *Department of Biochemistry and Cell Biology and Institute for Cell and Developmental Biology, Stony Brook University, Stony Brook, NY 11794
- To whom correspondence may be addressed. E-mail:
or
| | - Huilin Li
- Biology Department, Brookhaven National Laboratory, Upton, NY 11973-5000; and
- To whom correspondence may be addressed. E-mail:
or
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3
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Frank CG, Aebi M. ALG9 mannosyltransferase is involved in two different steps of lipid-linked oligosaccharide biosynthesis. Glycobiology 2005; 15:1156-63. [PMID: 15987956 DOI: 10.1093/glycob/cwj002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
N-linked protein glycosylation follows a conserved pathway in eukaryotic cells. The assembly of the lipid-linked core oligosaccharide Glc3Man9GlcNAc2, the substrate for the oligosaccharyltransferase (OST), is catalyzed by different glycosyltransferases located at the membrane of the endoplasmic reticulum (ER). The substrate specificity of the different glycosyltransferase guarantees the ordered assembly of the branched oligosaccharide and ensures that only completely assembled oligosaccharide is transferred to protein. The glycosyltransferases involved in this pathway are highly specific, catalyzing the addition of one single hexose unit to the lipid-linked oligosaccharide (LLO). Here, we show that the dolichylphosphomannose-dependent ALG9 mannosyltransferase is the exception from this rule and is required for the addition of two different alpha-1,2-linked mannose residues to the LLO. This report completes the list of lumen-oriented glycosyltransferases required for the assembly of the LLO.
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Affiliation(s)
- Christian G Frank
- Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology Zürich, ETH Hönggerberg, CH-8093 Zürich, Switzerland
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4
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Chen W, Bucaria J, Band DA, Sutton A, Sternglanz R. Enp1, a yeast protein associated with U3 and U14 snoRNAs, is required for pre-rRNA processing and 40S subunit synthesis. Nucleic Acids Res 2003; 31:690-9. [PMID: 12527778 PMCID: PMC140510 DOI: 10.1093/nar/gkg145] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2002] [Revised: 11/13/2002] [Accepted: 11/13/2002] [Indexed: 11/14/2022] Open
Abstract
ENP1 is an essential Saccharomyces cerevisiae gene encoding a 483 amino acid polypeptide. Enp1 protein is localized in the nucleus and concentrated in the nucleolus. An enp1-1 temperature-sensitive mutant inhibited 35S pre-rRNA early processing at sites A(0), A(1) and A(2) as shown by northern analysis of steady state levels of rRNA precursors. Pulse-chase analysis further revealed that the enp1-1 strain was defective in the synthesis of 20S pre-rRNA and hence 18S rRNA, which led to reduced formation of 40S ribosomal subunits. Co-precipitation analysis revealed that Enp1 was associated with Nop1 protein, as well as with U3 and U14 RNAs, two snoRNAs implicated in early pre-rRNA processing steps. These results suggest a direct role for Enp1 in the early steps of rRNA processing.
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Affiliation(s)
- Weidong Chen
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA
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5
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Yan Q, Lennarz WJ. Studies on the function of oligosaccharyl transferase subunits: a glycosylatable photoprobe binds to the luminal domain of Ost1p. Proc Natl Acad Sci U S A 2002; 99:15994-9. [PMID: 12444261 PMCID: PMC138553 DOI: 10.1073/pnas.212637999] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/21/2002] [Indexed: 12/24/2022] Open
Abstract
Oligosaccharyl transferase (OT) is a complex multisubunit enzyme that, in the case of Saccharomyces cerevisiae, contains nine different transmembrane proteins. One of our goals is to identify the OT subunit(s) responsible for recognizing the consensus sequence, -Asn-X-ThrSer-, and catalyzing the oligosaccharide transfer reaction. By using a substrate-based photoprobe, earlier we found that Ost1p was specifically linked to the radiolabeled photoprobe. We have now examined Ost1p in more detail. Deletion of the cytoplasmic tail of Ost1p caused no defects in growth and glycosylation. In addition, replacement of the transmembrane domain with other hydrophobic amino acids did not impair growth. In contrast, a construct containing only the luminal domain of Ost1p did not support cell growth. Given these observations, we concentrated on studying the luminal domain of Ost1p and localized the photoprobe attachment region within a sequence of nine amino acid residues. Because mutations in the photoprobe attachment region did not cause any severe growth or glycosylation defects, we conclude that this region is not involved in the recognition of the N-glycosylation site. By further mutagenesis of the conserved residues of Ost1p we conclude that the luminal domain mediates interactions with other subunits of OT and becomes labeled because of its proximity to the recognition andor catalytic subunit in the OT complex, Stt3p.
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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, Stony Brook, NY 11794-5215, USA
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6
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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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7
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Yan Q, Lennarz WJ. Oligosaccharyltransferase: a complex multisubunit enzyme of the endoplasmic reticulum. Biochem Biophys Res Commun 1999; 266:684-9. [PMID: 10603306 DOI: 10.1006/bbrc.1999.1886] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The attachment of N-linked oligosaccharide chains to proteins is an important cotranslational process. These chains can, in some cases, serve to stabilize the protein, while in other cases they function as recognition elements. A key enzyme in the N-glycosylation process is oligosaccharyltransferase (OT). In yeast this enzyme, which is found in the endoplasmic reticulum, consists of nine different transmembrane protein subunits. Our general aim is to learn more about the functions of the multiple subunits of yeast OT and their mode of interaction with each other. Using a combination of biochemical and genetic techniques the subunit Ost1p has been shown to recognize Asn-X-Ser/Thr glycosylation sites. The principle tool used in the identification process was a benzophenone-based glycosylation site peptide that was shown to be crosslinked to Ost1p. Our current objective is to identify the domain in the primary structure that is involved in recognition of the glycosylation site sequence. By use of bifunctional crosslinkers, the possible interaction of Ost1p with other subunits of OT will be studied. This work and other studies on the OT subunits are concisely summarized.
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Affiliation(s)
- Q Yan
- Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, New York, 11794, USA
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8
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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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9
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Abstract
The oligosaccharide substrate for the N-linked protein glycosylation is assembled at the membrane of the endoplasmic reticulum. Dolichyl pyrophosphate serves as a carrier in this biosynthetic pathway. In this review, we discuss the function of the lipid carrier dolichol in oligosaccharide assembly and give an overview of the biosynthesis of the different sugar donors required for the building of the oligosaccharide. Yeast genetic techniques have made it possible to identify many different loci encoding specific glycosyltransferases required for the precise and ordered assembly of the dolichyl pyrophosphate-linked oligosaccharide. Based on the knowledge obtained from studying this pathway in yeast, we compare it to the process of N-linked protein glycosylation in archaea. We suggest that N-linked glycosylation in eukaryotes and in archaea share a common evolutionary origin.
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Affiliation(s)
- P Burda
- Mikrobiologisches Institut, ETH Zürich, Schmelzbergstr. 7, CH-092 Zürich, Switzerland
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10
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Knauer R, Lehle L. The oligosaccharyltransferase complex from yeast. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1426:259-73. [PMID: 9878773 DOI: 10.1016/s0304-4165(98)00128-7] [Citation(s) in RCA: 164] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
N-Glycosylation of eukaryotic secretory and membrane-bound proteins is an essential and highly conserved protein modification. The key step of this pathway is the en bloc transfer of the high mannose core oligosaccharide Glc3Man9GlcNAc2 from the lipid carrier dolichyl phosphate to selected Asn-X-Ser/Thr sequences of nascent polypeptide chains during their translocation across the endoplasmic reticulum membrane. The reaction is catalysed by the enzyme oligosaccharyltransferase (OST). Recent biochemical and molecular genetic studies in yeast have yielded novel insights into this enzyme with multiple tasks. Nine proteins have been shown to be OST components. These are assembled into a heterooligomeric membrane-bound complex and are required for optimal expression of OST activity in vivo in wild type cells. In accord with the evolutionary conservation of core N-glycosylation, there are significant homologies between the protein sequences of OST subunits from yeast and higher eukaryotes, and OST complexes from different sources show a similar organisation as well.
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Affiliation(s)
- R Knauer
- Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, 93040 Regensburg, Germany
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11
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Suzuki T, Park H, Kitajima K, Lennarz WJ. Peptides glycosylated in the endoplasmic reticulum of yeast are subsequently deglycosylated by a soluble peptide: N-glycanase activity. J Biol Chem 1998; 273:21526-30. [PMID: 9705282 DOI: 10.1074/jbc.273.34.21526] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Several lines of evidence suggest that soluble peptide:N-glycanase (PNGase) is involved in the quality control system for newly synthesized glycoproteins in mammalian cells. Here we report the occurrence of a soluble PNGase activity in Saccharomyces cerevisiae. The enzyme, which was recovered in the cytosolic fraction, has a neutral pH optimum, and dithiothreitol is required for activity. All of these properties were similar to those of earlier described for mammalian PNGases. Interestingly, the yeast enzyme activity was found to be present almost exclusively in cells in stationary phase; little activity was detected in logarithmic growth phase cells. Upon incubation of a glycosylatable peptide R-Asn-X-Thr-R' with permeabilized yeast spheroplasts, we detected formation of both glycosylated peptide and the peptide product expected from PNGase-mediated deglycosylation of this glycopeptide, namely, R-Asp-X-Thr-R'. Recent findings that yeast have an active system for the retrograde transport of unfolded (glyco)proteins and glycopeptides out of the endoplasmic reticulum (ER) into the cytosol raise the possibility that this PNGase may participate in an early step in degradation of these molecules following their export from the ER.
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Affiliation(s)
- T Suzuki
- 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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12
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Kukuruzinska MA, Lennon K. Protein N-glycosylation: molecular genetics and functional significance. CRITICAL REVIEWS IN ORAL BIOLOGY AND MEDICINE : AN OFFICIAL PUBLICATION OF THE AMERICAN ASSOCIATION OF ORAL BIOLOGISTS 1998; 9:415-48. [PMID: 9825220 DOI: 10.1177/10454411980090040301] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Protein N-glycosylation is a metabolic process that has been highly conserved in evolution. In all eukaryotes, N-glycosylation is obligatory for viability. It functions by modifying appropriate asparagine residues of proteins with oligosaccharide structures, thus influencing their properties and bioactivities. N-glycoprotein biosynthesis involves a multitude of enzymes, glycosyltransferases, and glycosidases, encoded by distinct genes. The majority of these enzymes are transmembrane proteins that function in the endoplasmic reticulum and Golgi apparatus in an ordered and well-orchestrated manner. The complexity of N-glycosylation is augmented by the fact that different asparagine residues within the same polypeptide may be modified with different oligosaccharide structures, and various proteins are distinguished from one another by the characteristics of their carbohydrate moieties. Furthermore, biological consequences of derivatization of proteins with N-glycans range from subtle to significant. In the past, all these features of N-glycosylation have posed a formidable challenge to an elucidation of the physiological role for this modification. Recent advances in molecular genetics, combined with the availability of diverse in vivo experimental systems ranging from yeast to transgenic mice, have expedited the identification, isolation, and characterization of N-glycosylation genes. As a result, rather unexpected information regarding relationships between N-glycosylation and other cellular functions--including secretion, cytoskeletal organization, proliferation, and apoptosis--has emerged. Concurrently, increased understanding of molecular details of N-glycosylation has facilitated the alignment between N-glycosylation deficiencies and human diseases, and has highlighted the possibility of using N-glycan expression on cells as potential determinants of disease and its progression. Recent studies suggest correlations between N-glycosylation capacities of cells and drug sensitivities, as well as susceptibility to infection. Therefore, knowledge of the regulatory features of N-glycosylation may prove useful in the design of novel therapeutics. While facing the demanding task of defining properties, functions, and regulation of the numerous, as yet uncharacterized, N-glycosylation genes, glycobiologists of the 21st century offer exciting possibilities for new approaches to disease diagnosis, prevention, and cure.
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Affiliation(s)
- M A Kukuruzinska
- Department of Molecular and Cell Biology, School of Dental Medicine, Boston University Medical Center, Massachusetts 02118, USA
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13
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Ermonval M, Cacan R, Gorgas K, Haas IG, Verbert A, Buttin G. Differential fate of glycoproteins carrying a monoglucosylated form of truncated N-glycan in a new CHO line, MadIA214214, selected for a thermosensitive secretory defect. J Cell Sci 1997; 110 ( Pt 3):323-36. [PMID: 9057085 DOI: 10.1242/jcs.110.3.323] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A temperature sensitive secretory line, MadIA214, was selected from mutagenized Chinese hamster ovary cells that express two heterologous export marker proteins: a secretory form of the human placental alkaline phosphatase (SeAP), and the Kd heavy chain of mouse MHC class I. SeAP secretion in MadIA214 was extremely reduced at elevated temperature (40 degrees C), while the export of functional H-2Kd molecules to the plasma membrane was only slightly affected. This mutant constitutively transferred onto newly synthesized proteins a truncated oligosaccharide core, Man5GlcNAc2, which was monoglucosylated in the protein-bound form. Nevertheless, the final oligosaccharide-structures associated to mature SeAP and H-2Kd were similar in mutant and wild-type glycoproteins. The inaccessibility in MadIA214 endoplasmic reticulum (ER) of one or more components required for oligosaccharide chain elongation is supported by the reconstitution of a correct core structure, obtained after disruption of cellular compartments, but not after cell permeabilisation or blocking ER-to-Golgi transport. The increased association of the ER-chaperone BiP with immature SeAP correlated with the thermodependent decrease in SeAP secretion. The retention of incompletely folded polypeptides in MadIA214 parallels both a marked ER-dilation and an important glycoprotein degradation documented by the formation of soluble oligomannosides with one GlcNAc residue. Our data provide the first in vivo evidence that the initial step in N-glycosylation differentially governs glycoprotein maturation, transport and degradation.
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Affiliation(s)
- M Ermonval
- Unité de Génétique Somatique, URA CNRS 1960, Institut Pasteur, Paris, France.
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14
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Roos J, Luz JM, Centoducati S, Sternglanz R, Lennarz WJ. ENP1, an essential gene encoding a nuclear protein that is highly conserved from yeast to humans. Gene 1997; 185:137-46. [PMID: 9034325 DOI: 10.1016/s0378-1119(96)00661-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A novel gene in Saccharomyces cerevisiae, ENP1, was found to be essential for growth. The ENP1 gene encodes a protein of 483 amino acids (aa). Nucleotide sequence analysis revealed that the deduced aa sequence of this gene exhibited approx. 60% sequence similarity to the deduced aa sequence of proteins of unknown function in Drosophila, Caenorhabditis elegans and humans. No well defined functional motifs were evident upon analysis of the aa sequence. The protein was found to contain 20% acidic aa residues, with most of them being localized to a very negatively charged domain between aa residues 100 and 150. A construct encoding a fusion protein consisting of the Enp1 protein fused to the c-myc epitope that was either under the control of the ENP1 promoter or the GAL1,10 promoter was prepared. The construct was used to express the protein tagged with the c-myc epitope. Despite the presence of a naturally occurring promoter region with homology to the unfolded protein response element, the level of Enp1mycp remained unchanged after growth of the cells in the presence of tunicamycin, an inhibitor of N-linked glycosylation of proteins. Immunohistochemical studies to define the cellular localization of the Enp1myc protein revealed that it was localized to the nucleus. Accession No.: U50779.
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Affiliation(s)
- J Roos
- Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, SUNY at Stony Brook, NY 11794-5215, USA
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15
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Sagami H, Igarashi Y, Tateyama S, Ogura K, Roos J, Lennarz WJ. Enzymatic formation of dehydrodolichal and dolichal, new products related to yeast dolichol biosynthesis. J Biol Chem 1996; 271:9560-6. [PMID: 8621629 DOI: 10.1074/jbc.271.16.9560] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Two new polyprenyl products in addition to dehydrodolichol and dolichol were detected by two-plate silica gel thin layer chromatography of nonpolar products formed from [1-14C]isopentenyl diphosphate and farnesyl diphosphate in the reaction with a crude 1,000 x g supernatant of yeast homogenates in the presence of NADPH. The new products were indistinguishable from authentic dehydrodolichal and dolichal. Analyses of the time-dependent and pH-dependent formation of the four products including dehydrodolichal and dolichal suggested that the biosynthetic pathway from dehydrodolichol leading to dolichal is different from that to dolichol. In double-labeled experiments with a combination of -l-14C-isopentenyl diphosphate and a [4B-3H]NADPH-generating system, the ratio of 3H- and 14C-derived radioactivities found in dolichal was six times higher than that in dolichol. A small amount of 3H-labeled dehydrodolichol was also detected. Considering the fact that dolichol is synthesized from dehydrodolichol (Sagami, H., Kurisaki, A., and Ogura, K. (1993) J. Biol. Chem. 268, 10109-10113), we propose that dehydrodolichol is a common branch point intermediate in the biosynthetic pathways leading to dolichal and dolichol and that dehydrodolichal is an intermediate in the pathway from dehydrodolichol to dolichal.
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Affiliation(s)
- H Sagami
- Institute for Chemical Reaction Science, Tohoku University, Katahira, Sendai, Japan
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16
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Chi JH, Roos J, Dean N. The OST4 gene of Saccharomyces cerevisiae encodes an unusually small protein required for normal levels of oligosaccharyltransferase activity. J Biol Chem 1996; 271:3132-40. [PMID: 8621712 DOI: 10.1074/jbc.271.6.3132] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Sodium vanadate is an effective drug for the enrichment of yeast mutants defective in glycosylation reactions that are carried out in the Golgi complex. We have isolated vanadate-resistant, hygromycin B-sensitive mutants that act at very early steps of N-linked glycosylation, occurring in the endoplasmic reticulum. Here we describe the phenotypic characterization of ost4, a vanadate-resistant mutant that is defective in oligosaccharyltransferase (OTase) activity both in vivo and in vitro. The OST4 open reading frame is unusual in that it predicts a protein of only 36 amino acids. We demonstrate that the OST4 gene product is, in fact, an unusually small protein of approximately 3.6 kDa, predicted to lie almost entirely in the hydrophobic environment of the membrane. Strains carrying a disruption of the OST4 gene are viable but grow poorly at 25 degrees C. The null mutant is inviable at 37 degrees C, demonstrating that the OST4 gene product is essential for growth at high temperatures. Deletion of the OST4 gene greatly diminishes OTase activity but does not abolish it. These results suggest that the OST4 gene encodes a subunit or accessory component of OTase that is essential at high temperature.
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Affiliation(s)
- J H Chi
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215, USA
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17
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Over-expression ofS. cerevisiae G1 cyclins restores the viability ofalg1 N-glycosylation mutants. Curr Genet 1996. [DOI: 10.1007/bf02221573] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Benton BK, Plump SD, Roos J, Lennarz WJ, Cross FR. Over-expression of S. cerevisiae G1 cyclins restores the viability of alg1 N-glycosylation mutants. Curr Genet 1996; 29:106-13. [PMID: 8821656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In budding yeast, one of three G1 cyclins is required for progression though START, when cells commit to a further round of cell division. We have identified mutations in ALG1 (ERC14), a gene required for N-glycosylation, which are inviable in a cln1 cln2 background but are rescued by over-expression of CLNs. CLN1 and CLN2 are much more efficient than CLN3 in rescuing the erc14-1 allele. The erc14-1 allele results in a significant N-glycosylation defect, and no rescue of this defect by CLN1 over-expression was detected. These data suggest that CLN over-expression could be allowing cells to live with lower levels of N-glycosylation, possibly by overcoming a checkpoint sensitive to N-glycosylation capacity. A plasmid suppressor of alg1, PSA1, encodes a 361 amino-acid protein with homology to NDP-hexose pyrophosphorylases, the enzymes that catalyze the formation of activated sugar nucleotides. PSA1 is an essential gene, and PSA1 transcription is nearly co-ordinately regulated with CLN2 transcription, peaking near START. Co-ordinate regulation of glycosylation, sugar nucleotide metabolism, and cell-cycle progression through G1 may be a feature that ensures adequate cell-wall precursors are present before bud emergence.
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Affiliation(s)
- B K Benton
- Rockefeller University, New York, NY 10021, USA
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Abstract
Aminoglycosides are a therapeutically important class of antibiotics that inhibit bacterial protein synthesis and a number of viral and eukaryotic functions by blocking RNA-protein interactions. Vanadate-resistant Saccharomyces cerevisiae mutants with defects in Golgi-specific glycosylation processes exhibit growth sensitivity to hygromycin B, an aminoglycoside [Ballou, L., Hitzeman, R. A., Lewis, M. S. & Ballou, C. E. (1991) Proc. Natl. Acad. Sci. USA 88, 3209-3212]. Here, evidence is presented that glycosylation is, in and of itself, a key factor mediating aminoglycoside sensitivity in yeast. Examination of mutants with a wide range of glycosylation abnormalities reveals that all are sensitive to aminoglycosides. This effect is specific to aminoglycosides and not merely a consequence of increased permeability of the yeast mutants to drugs. Furthermore, inhibition of glycosylation in wild-type cells leads to a marked increase in their sensitivity to aminoglycosides. These results establish that a defect in glycosylation is sufficient to render yeast cells susceptible to these clinically important drugs. Further, they suggest that a molecule which prevents the uptake or mediates removal of aminoglycosides requires glycosylation for its activity. Perhaps more importantly, this finding on drug sensitivity provides the most powerful screen to date to identify mutants and thereby to isolate genes involved in all aspects of N-linked glycosylation.
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Affiliation(s)
- N Dean
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook 11794-5215
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