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Kellokumpu S, Hassinen A, Glumoff T. Glycosyltransferase complexes in eukaryotes: long-known, prevalent but still unrecognized. Cell Mol Life Sci 2016; 73:305-25. [PMID: 26474840 PMCID: PMC7079781 DOI: 10.1007/s00018-015-2066-0] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Revised: 09/28/2015] [Accepted: 10/08/2015] [Indexed: 01/08/2023]
Abstract
Glycosylation is the most common and complex cellular modification of proteins and lipids. It is critical for multicellular life and its abrogation often leads to a devastating disease. Yet, the underlying mechanistic details of glycosylation in both health and disease remain unclear. Partly, this is due to the complexity and dynamicity of glycan modifications, and the fact that not all the players are taken into account. Since late 1960s, a vast number of studies have demonstrated that glycosyltransferases typically form homomeric and heteromeric complexes with each other in yeast, plant and animal cells. To propagate their acceptance, we will summarize here accumulated data for their prevalence and potential functional importance for glycosylation focusing mainly on their mutual interactions, the protein domains mediating these interactions, and enzymatic activity changes that occur upon complex formation. Finally, we will highlight the few existing 3D structures of these enzyme complexes to pinpoint their individual nature and to emphasize that their lack is the main obstacle for more detailed understanding of how these enzyme complexes interact and function in a eukaryotic cell.
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Affiliation(s)
- Sakari Kellokumpu
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland.
| | - Antti Hassinen
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland
| | - Tuomo Glumoff
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland
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Hassinen A, Kellokumpu S. Organizational interplay of Golgi N-glycosyltransferases involves organelle microenvironment-dependent transitions between enzyme homo- and heteromers. J Biol Chem 2014; 289:26937-26948. [PMID: 25135644 DOI: 10.1074/jbc.m114.595058] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Glycosylation of proteins and lipids takes place in the Golgi apparatus by the consecutive actions of functionally distinct glycosidases and glycosyltransferases. Current evidence indicates that they function as enzyme homomers and/or heteromers in the living cell. Here we investigate their organizational interplay and show that glycosyltransferase homomers are assembled in the endoplasmic reticulum. Upon transport to the Golgi, the majority of homomers are disassembled to allow the formation of enzyme heteromers between sequentially acting medial-Golgi enzymes GnT-I and GnT-II or trans-Golgi enzymes GalT-I and ST6Gal-I. This transition is driven by the acidic Golgi environment, as it was markedly inhibited by raising Golgi luminal pH with chloroquine. Our FRAP (fluorescence recovery after photobleaching) measurements showed that the complexes remain mobile Golgi membrane constituents that can relocate to the endoplasmic reticulum or to the scattered Golgi mini-stacks upon brefeldin A or nocodazole treatment, respectively. During this relocation, heteromers undergo a reverse transition back to enzyme homomers. These data unveil an unprecedented organizational interplay between Golgi N-glycosyltransferases that involves dynamic and organelle microenvironment-driven transitions between enzyme homomers and heteromers during their trafficking within the early secretory compartments.
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Affiliation(s)
- Antti Hassinen
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, FI-90220, Oulu, Finland
| | - Sakari Kellokumpu
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, FI-90220, Oulu, Finland.
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Tvaroška I, Kozmon S, Wimmerová M, Koča J. A QM/MM investigation of the catalytic mechanism of metal-ion-independent core 2 β1,6-N-acetylglucosaminyltransferase. Chemistry 2013; 19:8153-62. [PMID: 23616464 DOI: 10.1002/chem.201300383] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Revised: 03/15/2013] [Indexed: 12/21/2022]
Abstract
β1,6-GlcNAc-transferase (C2GnT) is an important controlling factor of biological functions for many glycoproteins and its activity has been found to be altered in breast, colon, and lung cancer cells, in leukemia cells, in the lymhomonocytes of multiple sclerosis patients, leukocytes from diabetes patients, and in conditions causing an immune deficiency. The result of the action of C2GnT is the core 2 structure that is essential for the further elongation of the carbohydrate chains of O-glycans. The catalytic mechanism of this metal-ion-independent glycosyltransferase is of paramount importance and is investigated here by using quantum mechanical (QM) (density functional theory (DFT))/molecular modeling (MM) methods with different levels of theory. The structural model of the reaction site used in this report is based on the crystal structures of C2GnT. The entire enzyme-substrate system was subdivided into two different subsystems: the QM subsystem containing 206 atoms and the MM region containing 5914 atoms. Three predefined reaction coordinates were employed to investigate the catalytic mechanism. The calculated potential energy surfaces discovered the existence of a concerted SN 2-like mechanism. In this mechanism, a nucleophilic attack by O6 facilitated by proton transfer to the catalytic base and the separation of the leaving group all occur almost simultaneously. The transition state for the proposed reaction mechanism at the M06-2X/6-31G** (with diffuse functions on the O1', O5', OGlu , and O6 atoms) level was located at C1-O6=1.74 Å and C1-O1=2.86 Å. The activation energy for this mechanism was estimated to be between 20 and 29 kcal mol⁻¹, depending on the method used. These calculations also identified a low-barrier hydrogen bond between the nucleophile O6H and the catalytic base Glu320, and a hydrogen bond between the N-acetamino group and the glycosidic oxygen of the donor in the TS. It is proposed that these interactions contribute to a stabilization of TS and participate in the catalytic mechanism.
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Affiliation(s)
- Igor Tvaroška
- Institute of Chemistry, Slovak Academy of Sciences, 845 38 Bratislava, Slovak Republic.
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Tarr JM, Ding N, Kaul K, Antonell A, Pérez-Jurado LA, Chibber R. Cellular crosstalk between TNF-α, NADPH oxidase, PKCβ2, and C2GNT in human leukocytes. Cell Signal 2012; 24:873-8. [DOI: 10.1016/j.cellsig.2011.12.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Revised: 11/22/2011] [Accepted: 12/04/2011] [Indexed: 01/31/2023]
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Pak JE, Satkunarajah M, Seetharaman J, Rini JM. Structural and Mechanistic Characterization of Leukocyte-Type Core 2 β1,6-N-Acetylglucosaminyltransferase: A Metal-Ion-Independent GT-A Glycosyltransferase. J Mol Biol 2011; 414:798-811. [DOI: 10.1016/j.jmb.2011.10.039] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Revised: 10/14/2011] [Accepted: 10/21/2011] [Indexed: 10/15/2022]
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Cheng PW, Radhakrishnan P. Mucin O-glycan branching enzymes: structure, function, and gene regulation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2011; 705:465-92. [PMID: 21618125 DOI: 10.1007/978-1-4419-7877-6_25] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Pi-Wan Cheng
- Department of Biochemistry and Molecular Biology, College of Medicine and Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198-5870, USA.
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Yen TY, Macher BA. Determination of glycosylation sites and disulfide bond structures using LC/ESI-MS/MS analysis. Methods Enzymol 2007; 415:103-13. [PMID: 17116470 DOI: 10.1016/s0076-6879(06)15007-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/15/2023]
Abstract
Significant progress has been made in discovering and cloning a host of proteins, including a range of glycoproteins. The availability of their predicted amino acid sequences provides useful information, including potential N-linked glycosylation sites. However, only a limited number of protein structures have been solved, and very little is known about the structures of membrane proteins. One of the important structural elements of a protein is its disulfide bonds. These covalent bonds place conformational constraints on the overall protein structure, and thus, their identification provides important structural information. A second important posttranslational modification found in proteins is N-linked glycosylation. Although potential sites of N-linked glycosylation can be predicted from a protein's primary sequence based on the presence of N-X-S/T sequences, not all of the predicted sites will be glycosylated. Therefore, N-linked glycosylation sites must be located by structural analysis. We have developed a simple and sensitive method for determining the presence of free cysteine (Cys) residues and disulfide-bonded Cys residues, as well as the N-linked glycosylation sites in glycoproteins by liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) in combination with protein database searching using the programs Sequest and Mascot. The details of our method are described in this chapter.
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Affiliation(s)
- Ten-Yang Yen
- Department of Chemistry and Biochemistry, San Francisco State University, CA, USA
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Pak JE, Arnoux P, Zhou S, Sivarajah P, Satkunarajah M, Xing X, Rini JM. X-ray crystal structure of leukocyte type core 2 beta1,6-N-acetylglucosaminyltransferase. Evidence for a convergence of metal ion-independent glycosyltransferase mechanism. J Biol Chem 2006; 281:26693-701. [PMID: 16829524 DOI: 10.1074/jbc.m603534200] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Leukocyte type core 2 beta1,6-N-acetylglucosaminyltransferase (C2GnT-L) is a key enzyme in the biosynthesis of branched O-glycans. It is an inverting, metal ion-independent family 14 glycosyltransferase that catalyzes the formation of the core 2 O-glycan (Galbeta1-3[GlcNAcbeta1-6]GalNAc-O-Ser/Thr) from its donor and acceptor substrates, UDP-GlcNAc and the core 1 O-glycan (Galbeta1-3GalNAc-O-Ser/Thr), respectively. Reported here are the x-ray crystal structures of murine C2GnT-L in the absence and presence of the acceptor substrate Galbeta1-3GalNAc at 2.0 and 2.7A resolution, respectively. C2GnT-L was found to possess the GT-A fold; however, it lacks the characteristic metal ion binding DXD motif. The Galbeta1-3GalNAc complex defines the determinants of acceptor substrate binding and shows that Glu-320 corresponds to the structurally conserved catalytic base found in other inverting GT-A fold glycosyltransferases. Comparison of the C2GnT-L structure with that of other GT-A fold glycosyltransferases further suggests that Arg-378 and Lys-401 serve to electrostatically stabilize the nucleoside diphosphate leaving group, a role normally played by metal ion in GT-A structures. The use of basic amino acid side chains in this way is strikingly similar to that seen in a number of metal ion-independent GT-B fold glycosyltransferases and suggests a convergence of catalytic mechanism shared by both GT-A and GT-B fold glycosyltransferases.
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Affiliation(s)
- John E Pak
- Department of Molecular, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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Cabrera PV, Amano M, Mitoma J, Chan J, Said J, Fukuda M, Baum LG. Haploinsufficiency of C2GnT-I glycosyltransferase renders T lymphoma cells resistant to cell death. Blood 2006; 108:2399-406. [PMID: 16778138 PMCID: PMC1895562 DOI: 10.1182/blood-2006-04-018556] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Neoplastic T cells in mycosis fungoides (MF) are resistant to apoptotic agents, including galectin-1 that is abundant in skin. Although MF cells are typically CD7-, and thus galectin-1 resistant, CD7+ HH cells, derived from a patient with MF, were also resistant to galectin-1. HH cells demonstrate altered cell surface glycosylation, with loss of core 2 O-glycan ligands for galectin-1 created by core 2 beta1,6-N-acetylglucosaminyltransferase (C2GnT-I). Loss of core 2 O-glycans on tumor cells was also seen in primary CD7+ MF lesions. Surprisingly, HH cells are heterozygous for a C2GnT-I point mutation, yet this mutation resulted in a dramatic reduction in cellular glycosyltransferase activity. Expression of wild-type C2GnT-I in human HH cells, or murine lymphoma cells that lack C2GnT-I, restored core 2 O-glycan expression and susceptibility to galectin-1, whereas mutant enzyme lacked activity and did not restore core 2 O-glycan expression or susceptibility to galectin-1. Mutant enzyme did not have a dominant negative effect by affecting dimerization or activity of wild-type enzyme; rather, C2GnT-I haploinsufficiency is sufficient for loss of core 2 O-glycan expression and galectin-1 resistance. Thus, glycosyltransferase haploinsufficiency results in altered cellular glycosylation and resistance to cell death, identifying a new survival mechanism for T-lymphoma cells.
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Affiliation(s)
- Paula V Cabrera
- Department of Pathology, UCLA School of Medicine, 10833 Le Conte Ave, Los Angeles, CA 90095-1732, USA
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Affiliation(s)
- W W Young
- Department of Molecular, Cellular, and Craniofacial Biology, School of Dentistry, University of Louisville, Louisville, KY 40292, USA.
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Singh J, Khan GA, Kinarsky L, Cheng H, Wilken J, Choi KH, Bedows E, Sherman S, Cheng PW. Identification of disulfide bonds among the nine core 2 N-acetylglucosaminyltransferase-M cysteines conserved in the mucin beta6-N-acetylglucosaminyltransferase family. J Biol Chem 2004; 279:38969-77. [PMID: 15226299 DOI: 10.1074/jbc.m401046200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Bovine core 2 beta1,6-N-acetylglucosaminyltransferase-M (bC2GnT-M) catalyzes the formation of all mucin beta1,6-N-acetylglucosaminides, including core 2, core 4, and blood group I structures. These structures expand the complexity of mucin carbohydrate structure and thus the functional potential of mucins. The four known mucin beta1,6-N-acetylglucosaminyltransferases contain nine conserved cysteines. We determined the disulfide bond assignments of these cysteines in [(35)S]cysteine-labeled bC2GnT-M isolated from the serum-free conditioned medium of Chinese hamster ovary cells stably transfected with a pSecTag plasmid. This plasmid contains bC2GnT-M cDNA devoid of the 5'-sequence coding the cytoplasmic tail and transmembrane domain. The C18 reversed phase high performance liquid chromatographic profile of the tryptic peptides of reduced-alkylated (35)S-labeled C2GnT-M was established using microsequencing. Each cystine pair was identified by rechromatography of the C8 high performance liquid chromatographic radiolabeled tryptic peptides of alkylated bC2GnT-M on C18 column. Among the conserved cysteines in bC2GnT-M, the second (Cys(113)) was a free thiol, whereas the other eight cysteines formed four disulfide bridges, which included the first (Cys(73)) and sixth (Cys(230)), third (Cys(164)) and seventh (Cys(384)), fourth (Cys(185)) and fifth (Cys(212)), and eighth (Cys(393)) and ninth (Cys(425)) cysteine residues. This pattern of disulfide bond formation differs from that of mouse C2GnT-L, which may contribute to the difference in substrate specificity between these two enzymes. Molecular modeling using disulfide bond assignments and the fold recognition/threading method to search the Protein Data Bank found a match with aspartate aminotransferase structure. This structure is different from the two major protein folds proposed for glycosyltransferases.
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Affiliation(s)
- Jaswant Singh
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA
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