Mannosyl (Alpha-1,6-)-Glycoprotein Beta-1,6-N-Acetyl-Glucosaminyltransferase, Isozyme B (MGAT5B)

  • Kei-ichiro Inamori
  • Michael Pierce
  • Naoyuki Taniguchi
Reference work entry


Protein O-mannosylation is an essential modification in mammals, and the biological significance of the modification has been emerging as it has been linked with muscular dystrophy and other biological processes. In the brain, approximately 30 % of all O-linked glycans are O-mannose-initiated structures. O-Mannosylation is initiated by the addition of α-linked mannose to specific Ser and Thr residues by protein O-mannosyltransferase 1 (POMT1) and POMT 2, and subsequently a GlcNAc residue is added by protein O-mannosyl β-1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) to form the GlcNAc-β1,2-Man-α-O-Ser/Thr structure. A brain-specific β1,6-N-acetylglucosaminyltransferase IX (GnT-IX, GnT-VB, or MGAT5B) was cloned as a homolog of N-acetylglucosaminyltransferase V (GnT-V). GnT-V is ubiquitously expressed and involved in a variety of biological and pathological processes such as cytokine and growth factor receptor signaling. GnT-IX catalyzes the transfer of GlcNAc to the 6-OH position of α-linked mannose in GlcNAc-β1,2-Man-α sequence which is found in both N-glycans and O-mannosyl glycans. The ability of GnT-IX to transfer GlcNAc in β1,6 linkage to mannose initially identified using agalacto biantennary N-linked oligosaccharide substrate. After that time, GnT-IX was shown to transfer GlcNAc in β1,6 linkage towards the mannose in GlcNAc-β1,2-Man-α-O-Ser, as well to a synthetic peptide bearing the O-mannosyl disaccharide. It is now known that GnT-IX does not act on N-glycans in vivo but is responsible for the formation of β1,6GlcNAc-branch on O-mannosyl glycans in the brain. In addition, lower expression of GnT-IX was also observed in testis in mice and human.


Muscular Dystrophy Acceptor Substrate Polysialic Acid Congenital Muscular Dystrophy GlcNAc Residue 
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Copyright information

© Springer Japan 2014

Authors and Affiliations

  • Kei-ichiro Inamori
    • 1
  • Michael Pierce
    • 2
  • Naoyuki Taniguchi
    • 3
  1. 1.Division of Glycopathology, Institute of Molecular Biomembrane and GlycobiologyTohoku Pharmaceutical UniversitySendaiJapan
  2. 2.Department of Biochemistry and Molecular Biology, Complex Carbohydrate Research CenterThe University of GeorgiaAthensUSA
  3. 3.Disease Glycomics Team, Systems Glycobiology Research GroupRIKEN-Max Planck Joint Research Center for Systems Chemical Biology, Global Research Cluster, RIKENWakoJapan

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