N-glycan antennae elongation in the medial/trans-Golgi

Stable Identifier
Homo sapiens
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In the latter compartments of the distal Golgi the N-Glycan is further modified, leading to the wide range of N-Glycans observed in multicellular organisms. The first step of N-Glycan elongation in the Golgi is the addition of a GlcNAc residue on the alpha 1,3 branch by the enzyme MGAT1 (GlcNAc-TI), which commits the elongation pathway to Complex or Hybrid N-Glycans from Oligomannose N-Glycans. At this point, the pathway bifurcates again to generate Complex or Hybrid N-Glycans. The addition of a GlcNAc in the middle of the two arms of the N-Glycan, catalyzed by MGAT3 (GNT-III), inhibits the removal of the mannoses on the alpha1,3 branches by MAN2 and the addition of a GlcNAc by MGAT2 (GlcNAc-TII), and commits the pathway toward the synthesis of hybrid N-Glycans. Alternatively, the removal of these mannoses and the action of MGAT2 leads to the synthesis of complex N-Glycans (Kornfeld and Kornfeld 1985).
The exact structure of the network of reactions leading to Complex or Hybrid N-Glycans is still not completely described and validated experimentally. Here we will annotate only one generic reaction for each of the enzymes known to participate in this process. For a better annotation on the reactions and genes involved in the synthesis of Complex and Hybrid N-Glycans we recommend the GlycoGene Database (Ito H. et al, 2010) (http://riodb.ibase.aist.go.jp/rcmg/ggdb/textsearch.jsp) for annotations on genes, and the Consortium for Functional Genomics (http://riodb.ibase.aist.go.jp/rcmg/ggdb/textsearch.jsp) for annotation of Glycan structures and reactions. Moreover, a computationally inferred prediction on the structure of this network is available through the software GlycoVis (Hossler P. et. al. 2006).

Literature References
PubMed ID Title Journal Year
3896128 Assembly of asparagine-linked oligosaccharides

Kornfeld, S, Kornfeld, R

Annu Rev Biochem 1985
20816477 In vitro and in vivo enzymatic syntheses and mass spectrometric database for N-glycans and o-glycans

Ito, H, Narimatsu, H, Sato, T, Kameyama, A, Chiba, Y

Methods Enzymol 2010
11421343 The joys of HexNAc. The synthesis and function of N- and O-glycan branches

Schachter, H

Glycoconj J 2000
16807922 GlycoVis: visualizing glycan distribution in the protein N-glycosylation pathway in mammalian cells

Hu, WS, Lee, MM, Hossler, P, Goh, LT

Biotechnol Bioeng 2006
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