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2.4.1.101

Accepted name:

α-1,3-mannosyl-glycoprotein 2-β-N-acetylglucosaminyltransferase

Reaction:

UDP-N-acetyl-α-D-glucosamine + Man₅GlcNAc₂-[protein] = UDP + Man₅GlcNAc₃-[protein]

For diagram of mannosyl-glycoprotein N-acetylglucosaminyltransferases, click here

Glossary:

Man₅GlcNAc₂-[protein] = α-D-Man-(1→3)-[α-D-Man-(1→3)-[α-D-Man-(1→6)]-α-D-Man-(1→6)]-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-α-D-GlcNAc-N-Asn-[protein]
Man₅GlcNAc₃-[protein]= β-D-GlcNAc-(1→2)-α-D-Man-(1→3)-[α-D-Man-(1→3)-[α-D-Man-(1→6)]-α-D-Man-(1→6)]-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-α-D-GlcNAc-N-Asn-[protein]

Other name(s):

MGAT1 (gene name); N-acetylglucosaminyltransferase I; N-glycosyl-oligosaccharide-glycoprotein N-acetylglucosaminyltransferase I; uridine diphosphoacetylglucosamine-α-1,3-mannosylglycoprotein β-1,2-N-acetylglucosaminyltransferase; UDP-N-acetylglucosaminyl:α-1,3-D-mannoside-β-1,2-N-acetylglucosaminyltransferase I; UDP-N-acetylglucosaminyl:α-3-D-mannoside β-1,2-N-acetylglucosaminyltransferase I; α-1,3-mannosyl-glycoprotein β-1,2-N-acetylglucosaminyltransferase; GnTI; GlcNAc-T I; UDP-N-acetyl-D-glucosamine:3-(α-D-mannosyl)-β-D-mannosyl-glycoprotein 2-β-N-acetyl-D-glucosaminyltransferase

Systematic name:

UDP-N-acetyl-α-D-glucosamine:α-D-mannosyl-(1→3)-β-D-mannosyl-glycoprotein 2-β-N-acetyl-D-glucosaminyltransferase (configuration-inverting)

Comments:

The enzyme, found in plants and animals, participates in the processing of N-glycans in the Golgi apparatus. Its action is required before the other N-acetylglucosaminyltransferases involved in the process (GlcNAcT-II through VI) can act. While the natural substrate (produced by EC 3.2.1.113, mannosyl-oligosaccharide 1,2-α-mannosidase) is described here, the minimal substrate recognized by the enzyme is α-D-Man-(1→3)-β-D-Man-R.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 102576-81-8

References:

1.	Harpaz, N. and Schachter, H. Control of glycoprotein synthesis. Bovine colostrum UDP-N-acetylglucosamine:α-D-mannoside β2-N-acetylglucosaminyltransferase I. Separation from UDP-N-acetylglucosamine:α-D-mannoside β2-N-acetylglucosaminyltransferase II, partial purification, and substrate specificity. J. Biol. Chem. 255 (1980) 4885–4893. [PMID: 6445358]
2.	Mendicino, J., Chandrasekaran, E.V., Anumula, K.R. and Davila, M. Isolation and properties of α-D-mannose:β-1,2-N-acetylglucosaminyltransferase from trachea mucosa. Biochemistry 20 (1981) 967–976. [PMID: 6452163]
3.	Oppenheimer, C.L. and Hill, R.L. Purification and characterization of a rabbit liver α1→3 mannoside β1→2 N-acetylglucosaminyltransferase. J. Biol. Chem. 256 (1981) 799–804. [PMID: 6450208]
4.	Oppenheimer, C.L., Eckhardt, A.E. and Hill, R.L. The nonidentity of porcine N-acetylglucosaminyltransferases I and II. J. Biol. Chem. 256 (1981) 11477–11482. [PMID: 6457827]
5.	Miyagi, T. and Tsuiki, S. Studies on UDP-N-acetylglucosamine : α-mannoside β-N-acetylglucosaminyltransferase of rat liver and hepatomas. Biochim. Biophys. Acta 661 (1981) 148–157. [DOI] [PMID: 6170335]
6.	Schachter, H., Narasimhan, S., Gleeson, P. and Vella, G. Glycosyltransferases involved in elongation of N-glycosidically linked oligosaccharides of the complex or N-acetyllactosamine type. Methods Enzymol. 98 (1983) 98–134. [PMID: 6366476]
7.	Vella, G.J., Paulsen, H. and Schachter, H. Control of glycoprotein synthesis. IX. A terminal Man alphal-3Man β1- sequence in the substrate is the minimum requirement for UDP-N-acetyl-D-glucosamine: α-D-mannoside (GlcNAc to Man α1-3) β2-N-acetylglucosaminyltransferase I. Can. J. Biochem. Cell Biol. 62 (1984) 409–417. [PMID: 6235906]
8.	Unligil, U.M., Zhou, S., Yuwaraj, S., Sarkar, M., Schachter, H. and Rini, J.M. X-ray crystal structure of rabbit N-acetylglucosaminyltransferase I: catalytic mechanism and a new protein superfamily. EMBO J. 19 (2000) 5269–5280. [DOI] [PMID: 11032794]

[EC 2.4.1.101 created 1983, modified 2001 (EC 2.4.1.51 created 1972, part incorporated 1984), modified 2018]

3.2.1.113

Accepted name:

mannosyl-oligosaccharide 1,2-α-mannosidase

Reaction:

(1) Man₉GlcNAc₂-[protein] + 4 H₂O = Man₅GlcNAc₂-[protein] + 4 β-D-mannopyranose (overall reaction)
(1a) Man₉GlcNAc₂-[protein] + H₂O = Man₈GlcNAc₂-[protein] (isomer 8A_1,2,3B_1,2) + β-D-mannopyranose
(1b) Man₈GlcNAc₂-[protein] (isomer 8A_1,2,3B_1,2) + H₂O = Man₇GlcNAc₂-[protein] (isomer 7A_1,2,3B₂) + β-D-mannopyranose
(1c) Man₇GlcNAc₂-[protein] (isomer 7A_1,2,3B₂) + H₂O = Man₆GlcNAc₂-[protein] (isomer 6A_1,2B₂) + β-D-mannopyranose
(1d) Man₆GlcNAc₂-[protein] (isomer 6A_1,2B₂) + H₂O = Man₅GlcNAc₂-[protein] + β-D-mannopyranose
(2) Man₈GlcNAc₂-[protein] (isomer 8A_1,2,3B_1,3) + 3 H₂O = Man₅GlcNAc₂-[protein] + 3 β-D-mannopyranose (overall reaction)
(2a) Man₈GlcNAc₂-[protein] (isomer 8A_1,2,3B_1,3) + H₂O = Man₇GlcNAc₂-[protein] (isomer 7A_1,2,3B₁) + β-D-mannopyranose
(2b) Man₇GlcNAc₂-[protein] (isomer 7A_1,2,3B₁) + H₂O = Man₆GlcNAc₂-[protein] (isomer 6A_1,2,3) + β-D-mannopyranose
(2c) Man₆GlcNAc₂-[protein] (isomer 6A_1,2,3) + H₂O = Man₅GlcNAc₂-[protein] + β-D-mannopyranose

Glossary:

Man₉GlcNAc₂-[protein] = [α-D-Man-(1→2)-α-D-Man-(1→2)-α-D-Man-(1→3)-{α-D-Man-(1→2)-α-D-Man-(1→3)-[α-D-Man-(1→2)-α-D-Man-(1→6)]-α-D-Man-(1→6)}-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-β-D-GlcNAc]-N-Asn-[protein]
Man₈GlcNAc₂-[protein] (isomer 8A_1,2,3B_1,3) = [α-D-Man-(1→2)-α-D-Man-(1→2)-α-D-Man-(1→3)-{α-D-Man-(1→3)-[α-D-Man-(1→2)-α-D-Man-(1→6)]-α-D-Man-(1→6)}-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-β-D-GlcNAc]-N-Asn-[protein]
Man₅GlcNAc₂-[protein] = [α-D-Man-(1→3)-{α-D-Man-(1→3)-[α-D-Man-(1→6)]-α-D-Man-(1→6)}-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-β-D-GlcNAc]-N-Asn-[protein]

Other name(s):

mannosidase 1A; mannosidase 1B; 1,2-α-mannosidase; exo-α-1,2-mannanase; mannose-9 processing α-mannosidase; glycoprotein processing mannosidase I; mannosidase I; Man₉-mannosidase; ManI; 1,2-α-mannosyl-oligosaccharide α-D-mannohydrolase; MAN1A1 (gene name); MAN1A2 (gene name); MAN1C1 (gene name); 2-α-mannosyl-oligosaccharide α-D-mannohydrolase

Systematic name:

Man₉GlcNAc₂-[protein] α-2-mannohydrolase (configuration-inverting)

Comments:

This family of mammalian enzymes, located in the Golgi system, participates in the maturation process of N-glycans that leads to formation of hybrid and complex structures. The enzymes catalyse the hydrolysis of the four (1→2)-linked α-D-mannose residues from the Man₉GlcNAc₂ oligosaccharide attached to target proteins as described in reaction (1). Alternatively, the enzymes act on the Man₈GlcNAc₂ isomer formed by EC 3.2.1.209, endoplasmic reticulum Man₉GlcNAc₂ 1,2-α-mannosidase, as described in reaction (2). The enzymes are type II membrane proteins, require Ca²⁺, and use an inverting mechanism. While all three human enzymes can catalyse the reactions listed here, some of the enzymes can additionally catalyse hydrolysis in an alternative order, generating additional isomeric intermediates, although the final product is the same. The names of the isomers listed here are based on a nomenclature system proposed by Prien et al [7].

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9068-25-1

References:

1.	Tabas, I. and Kornfeld, S. Purification and characterization of a rat liver Golgi α-mannosidase capable of processing asparagine-linked oligosaccharides. J. Biol. Chem. 254 (1979) 11655–11663. [PMID: 500665]
2.	Tulsiani, D.R.P., Hubbard, S.C., Robbins, P.W. and Touster, O. α-D-Mannosidases of rat liver Golgi membranes. Mannosidase II is the GlcNAcMAN₅-cleaving enzyme in glycoprotein biosynthesis and mannosidases IA and IB are the enzymes converting Man₉ precursors to Man₅ intermediates. J. Biol. Chem. 257 (1982) 3660–3668. [PMID: 7061502]
3.	Bieberich, E. and Bause, E. Man₉-mannosidase from human kidney is expressed in COS cells as a Golgi-resident type II transmembrane N-glycoprotein. Eur. J. Biochem. 233 (1995) 644–649. [PMID: 7588811]
4.	Tremblay, L.O., Campbell Dyke, N. and Herscovics, A. Molecular cloning, chromosomal mapping and tissue-specific expression of a novel human α1,2-mannosidase gene involved in N-glycan maturation. Glycobiology 8 (1998) 585–595. [PMID: 9592125]
5.	Lal, A., Pang, P., Kalelkar, S., Romero, P.A., Herscovics, A. and Moremen, K.W. Substrate specificities of recombinant murine Golgi α1,2-mannosidases IA and IB and comparison with endoplasmic reticulum and Golgi processing α1,2-mannosidases. Glycobiology 8 (1998) 981–995. [PMID: 9719679]
6.	Tremblay, L.O. and Herscovics, A. Characterization of a cDNA encoding a novel human Golgi α 1, 2-mannosidase (IC) involved in N-glycan biosynthesis. J. Biol. Chem. 275 (2000) 31655–31660. [PMID: 10915796]
7.	Prien, J.M., Ashline, D.J., Lapadula, A.J., Zhang, H. and Reinhold, V.N. The high mannose glycans from bovine ribonuclease B isomer characterization by ion trap MS. J. Am. Soc. Mass Spectrom. 20 (2009) 539–556. [DOI] [PMID: 19181540]

[EC 3.2.1.113 created 1986, modified 2019]