Affordable Access

Enzymatic synthesis of Gb3 and iGb3 ceramides

Publication Date
  • Nkt Cells - Igb3
  • Gb3
  • Human Blood Group B Galactosyltransferase
  • α-(1→4)-Galactosyltransferase
  • Bovine α-(1→3)-Galactosyltransferase
  • Biology


Gb3 and iGb3 are physiologically important trihexosylceramides with a terminal α-d-Galp-(1→4)-β-d-Galp- and α-d-Galp-(1→3)-β-d-Galp sequence, respectively. In particular iGb3 is attracting considerable attention as it is believed to serve as a ligand for natural killer T cells. Whether or not iGb3 is present in humans and which enzyme might be responsible for its synthesis is at present a matter of lively debate. In the current investigation we evaluated human blood group B galactosyltransferase (GTB) for its ability to catalyze the formation of iGb3 from lactosylceramide and UDP-Galp. GTB is a retaining glycosyltransferase that in vivo catalyzes the transfer of galactose from UDP-Galp donors to OH-3 of Galp on the H-antigen (α-l-Fucp-(1→2)-β-d-Galp) acceptor forming the blood group B antigen. GTB tolerates modifications in donor and acceptor substrates and its ability to accept lactosides as acceptors makes it a possible candidate for iGb3 production in humans. For comparison iGb3 and Gb3 were also synthesized from the same acceptor using an α-(1→3)- and α-(1→4)-specific galactosyltransferase, respectively. All the enzymes tested catalyzed the desired reactions. Product characterization by NMR analysis clearly differentiated between the α-Galp-(1→3)-Galp and α-Galp-(1→4)-Galp product, with the GTB product being identical to that of the α-(1→3)-GalT-catalyzed reaction. The rate of transfer by GTB however was very low, only 0.001% of the rate obtained with a good substrate, H antigen disaccharide (octyl α-l-Fucp-(1→2)-β-d-Galp). This is too low to account for the possible formation of the iGb3 structure in humans in vivo.

There are no comments yet on this publication. Be the first to share your thoughts.


Seen <100 times