Harry Schachter Professor Emeritus

M.D., 1959
Ph.D., Toronto, 1964

Hospital for Sick Children, Research Institute, Room 3427B Hill Wing
416-813-5915
harry@sickkids.ca

Structure and Synthesis of Glycoproteins



Research Synopsis
 


  • (PhD project) - Active site of chymotrypsin. Identification of the methionine involved in the active center of chymotrypsin.
  • Research on the biosynthesis of glycoconjugates, primarily on the mechanisms of protein glycosylation.
  • Pathway of L-fucose catabolism in mammalian liver and enzymatic assay for L-fucose.
  • Synthesis of radioactive GDP-Fucose.
  • Intracellular localization of glycosyltransferases in a Golgi-rich fraction. First biochemical evidence supporting Leblond's histochemical data showing that the Golgi apparatus is a major site of glycosylation.
  • Serum contains glycosyltransferase activities involved in N-glycan and human blood group antigen synthesis. This work facilitated the study of blood group genetics at a time when the cloned glycosyltransferases were not yet available.
  • Qualitative differences in the N-acetyl-D-galactosaminyltransferases produced by human blood group A1 and A2 genes.
  • Branch specificity of ß4-Gal-transferase.
  • Discovery, characterization and synthesis of testis-specific sulfogalactoglycerolipid.
  • Glycoprotein glycosyltransferase levels during spermatogenesis.
  • Carbohydrate-binding specificities of various lectins.
  • Discovery and characterization of a rat liver Golgi a-D-mannosidase dependent on the prior action of UDP-N-acetylglucosamine:a-D-mannoside ß-2-N-acetylglucosaminyltransferase I. This activity was also described by the groups of Kornfeld and Touster and was subsequently named a-mannosidase II.

Discovery and characterization of novel glycosyltransferase activities.
This area has for many years been our major research interest. Among the important contributions in this area have been the discovery of several new glycosyltransferase activities, the naming of these enzymes (GnT I to VI and the core 1 to 4 O-glycan glycosyltransferases) and the delineation of ordered pathways of synthesis involving allowed ("GO") and non-allowed ("NO GO") steps in the pathway. Although we named GnT V, this enzyme was first described by Cummings and Kornfeld.

N-glycan synthesis:
  • N-glycan core a6- and a3-fucosyltransferase
  • ß2-GlcNAc-transferase I
  • ß2-GlcNAc-transferase II
  • ß4-GlcNAc-transferase III
  • ß4-GlcNAc-transferase IV
  • ß4-GlcNAc-transferase VI
O-glycan synthesis:
  • Core 1 ß3-Gal-transferase
  • Core 2 ß6-GlcNAc-transferase
  • Core 3 ß3-GlcNAc-transferase
  • Core 4 ß6-GlcNAc-transferase
  • Extension ß3-GlcNAc-transferase
Snail glycosyltransferases

Substrate specificity studies with synthetic substrates and analogues.

Studies on glycosyltransferase genes

  • Cloning and characterization of the gene encoding ß1,2-GlcNAc-transferase I.
  • Cloning and characterization of the gene encoding ß1,2-GlcNAc-transferase II.
  • Cloning and characterization of the gene encoding ß1,2-GlcNAc-transferase I.2. This enzyme was subsequently re-named Protein O-Mannosyl ß1,2-GlcNAc-transferase I (POMGnTI).
  • Determination of the crystal structure of ß1,2-GlcNAc-transferase I, in collaboration with Jim Rini.

Studies on the functions of N-glycans

  • Glycosyltransferases in various cancer systems.
  • Characterization of mice with null mutations in GlcNAc-transferase genes I, II and III, in collaboration with Jamey Marth.
  • Carbohydrate-Deficient Glycoprotein Syndrome type IIa is due to a defective GlcNAc-transferase II gene, in collaboration with Jaak Jaeken.
  • Structural and functional consequences of an N-glycosylation mutation in hereditary erythroblastic multinuclearity with a positive acidified serum test (HEMPAS) affecting human erythrocyte membrane glycoproteins, in collaboration with RAF Reithmeier.
Recent work on the role of glycosylation in development.
Work done in many laboratories, including ours, indicates the essential role of complex N-glycans in mammalian embryogenesis. This has led us to study the roles of complex N-glycans in the development of Caenorhabditis elegans and Drosophila melanogaster. We have cloned and characterized three C.elegans genes and one D.melanogaster gene encoding alpha-mannoside GlcNAc-transferase I and one gene encoding C.elegans alpha-mannoside GlcNAc-transferase II. We have reported on the phenotypes of worms with null mutations in the three GlcNAc-transferase I genes and flies with a null mutation in the GlcNAc-transferase I gene. Point mutations in the POMGnTI gene (first cloned by our group) have been shown by others to be responsible for a form of human congenital muscular dystrophy called Muscle-Eye-Brain (MEB) disease. We have developed an enzymatic diagnostic test for MEB using cultured cells.

Future Research
Functional Glycoproteomics using Caenorhabditis elegans and Drosophila melanogaster as model organisms. These projects will attempt to determine the precise molecular mechanisms whereby protein-bound N-glycans function in the development of a multicellular organism.

 


Selected Publications

Shi H, Tan J, Schachter H. N-glycans are involved in the response of Caenorhabditis elegans to bacterial pathogens. Methods in Enzymology (2006) 417:359-389.

Sarkar M, Leventis PA, Silvescu CI, Reinhold VN, Schachter H, Boulianne GL. Null mutations in Drosophila N-acetylglucosaminyltransferase I produce defects in locomotion and a reduced lifespan. J. Biol. Chem. (2006) 281 (18):12776-12785

Vajsar J, Zhang W, Dobyns WB, Biggar D, Holden KR, Hawkins C, Ray P, Olney AH, Burson CM, Srivastava AK, Schachter H. Carriers and patients with muscle-eye-brain disease can be rapidly diagnosed by enzymatic analysis of fibroblasts and lymphoblasts. Neuromuscular Disorders (2006) 16 (2): 132-136.

Fan X, She Y, Bagshaw RD, Callahan JW, Schachter H, Mahuran DJ. Identification of the hydrophobic glycoproteins of Caenorhabditis elegans. Glycobiology (2005) 15:952-964.

Zhu S, Hanneman A, Reinhold VN, Spence AM, Schachter H. Caenorhabditis elegans triple null mutant lacking UDP-N-acetyl-D-glucosamine:alpha-3-D-mannoside ß1,2-N-acetylglucosaminyltransferase I. Biochem.J. (2004) 382: 995-1001.

Fan X, She Y, Bagshaw RD, Callahan JW, Schachter H, Mahuran DJ. A method for proteomic identification of membrane-bound proteins containing Asn-linked oligosaccharides. Analytical Biochem. (2004) 332: 178-186.

Barresi R, Michele DE, Kanagawa M, Harper HA, Dovico SA, Satz JS, Moore SA, Zhang W, Schachter H, Dumanski JP, Cohn RD, Nishino I, Campbell KP. LARGE can functionally bypass alpha-dystroglycan glycosylation defects in distinct congenital muscular dystrophies. Nat. Med. (2004) 10: 696-703.

Zhang W, Vajsar J, Cao P, Breningstall G, Diesen C, Dobyns W, Herrmann R, Lehesjoki A-E, Steinbrecher A, Talim B, Toda T, Topaloglu H, Voit T, Schachter H. Enzymatic diagnostic test for Muscle-Eye-Brain type Congenital Muscular Dystrophy using commercially available reagents. Clinical Biochemistry. (2003) 36 (5): 339-344.

Zhang W, Cao P, Chen S, Spence AM, Zhu S, Staudacher E, Schachter H. Synthesis of paucimannose N-glycans by Caenorhabditis elegans requires prior actions of UDP-N-acetyl-D-glucosamine: alpha-3-D-mannoside ß1,2-N-acetylglucosaminyltransferase I, alpha3,6-mannosidase II and a specific membrane-bound ß-N-acetylglucosaminidase. Biochem.J. (2003) 372(1): 53-64.

Zhang W, Betel D, Schachter H. Cloning and Expression of a Novel UDP-GlcNAc: alpha-D-Mannoside ß1,2-N-Acetylglucosaminyltransferase Homologous to UDP-GlcNAc: alpha-3-D-Mannoside ß1,2-N-Acetylglucosaminyltransferase I. Biochemical J. (2002), 361:153-162.

Wang Y, Tan J, Sutton-Smith M, Ditto D, Panico M, Campbell RM, Varki NM, Long JM, Jaeken J, Levinson SR, Wynshaw-Boris A, Morris HR, Le D, Dell A, Schachter H, Marth JD. Modeling human congenital disorder of glycosylation type IIa in the mouse: conservation of asparagine-linked glycan-dependent functions in mammalian physiology and insights into disease pathogenesis. Glycobiology (2001), 11 (12): 1051-1070.

Sarkar M and Schachter H. Cloning and expression of Drosophila melanogaster UDP-GlcNAc:alpha-3-D-mannoside ß1,2-N-acetylglucosaminyltransferase I. Biol.Chem., 382: 209-217, 2001.

Mucha J, Svoboda B, Fröhwein U, Strasser R, Mischinger M, Schwihla H, Altmann F, Hane W, Schachter H. Glössl J, Mach L. Tissues of the clawed frog Xenopus laevis contain two closely related forms of UDP-GlcNAc: alpha3-D-mannoside ß-1,2-N-acetylglucosaminyltransferase I. Glycobiology, 11 (9): 769-778, 2001.

 

See also recent publications on PubMed


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