Synthesis of pentasaccharide analogues of the N-glycan substrates of N-acetylglucosaminyltransferases III, IV and V using tetrasaccharide precursors and recombinant beta-(1-->2)-N-acetylglucosaminyltransferase II

Use of synthetic oligosaccharide substrate analogs to map the active sites of N-acetylglucosaminyltransferases I and II

Tables III and IV summarize substrate analog data presented in Tables I and II, respectively. Data for GlcNAc-T I shown in Tables I and III correlate very well with the crystal structure for GlcNAc-T I. This indicates that substitution of the various hydroxyl groups by hydrogen, [table: see text] O-methyl, and maybe even larger O-alkyl groups does not cause appreciable changes to either the overall conformation of the oligosaccharide or the binding mode, thus supporting this approach of chemical modification of oligosaccharide substrates for mapping of the binding site. There is as yet no crystal structure for GlcNAc-T II. These studies indicate both advantages and disadvantages of this approach for elucidating the catalytic and binding sites of an enzyme. Substrate analog data indicate which chemical groups in the substrate are essential for catalysis and binding and suggest the type of linkage involved (hydrogen bond donor or acceptor). However, no information has been obtained on the protein groups involved in these interactions. If a crystal structure is available, the substrate analog conclusions are primarily confirmatory. However, whether or not a crystal structure is available, this approach can be very helpful in the design of specific inhibitors.

Molecular cloning and expression analysis of a mouse UDP-GlcNAc:Gal(beta1-4)Glc(NAc)-R beta1,3-N-acetylglucosaminyltransferase homologous to Drosophila melanogaster Brainiac and the beta1,3-galactosyltransferase family

We have isolated a murine cDNA coding for a beta1,3-N-acetylglucosaminyltransferase enzyme ( beta3GnT). This enzyme is similar in sequence to Drosophila melanogaster Brainiac and to the murine and human beta1,3-galactosyltransferase family of proteins. The mouse beta 3GnT protein is 397 amino acids in length and contains 7 cysteine residues that are conserved in the human orthologue. beta 3GnT is a type II membrane protein localized to the Golgi apparatus. Enzyme assays with recombinant mouse beta 3GnT reveal that it has a preference for acceptors with Gal(beta1-4)Glc(NAc) at the non-reducing termini. Proton NMR analysis of product showed incorporation of GlcNAc in beta1,3 linkage to the terminal Gal of Gal(beta1-4)Glc(beta1-O-benzyl). Northern blot analysis revealed the presence of a single 3.0[emsp4 ]kb transcript in all adult mouse and human organs tested, with highest levels in the kidney, liver, heart and placenta. The beta 3GnT gene is also expressed in a number of tumor cell lines. The human orthologue of beta 3GnT is located on chromosome 2pl5.

The joys of HexNAc. The synthesis and function of N- and O-glycan branches

This review covers discoveries made over the past 30-35 years that were important to our understanding of the synthetic pathway required for initiation of the antennae or branches on complex N-glycans and O-glycans. The review deals primarily with the author's contributions but the relevant work of other laboratories is also discussed. The focus of the review is almost entirely on the glycosyltransferases involved in the process. The following topics are discussed. (1) The localization of the synthesis of complex N-glycan antennae to the Golgi apparatus. (2) The "evolutionary boundary" at the stage in N-glycan processing where there is a change from oligomannose to complex N-glycans; this switch correlates with the appearance of multicellular organisms. (3) The discovery of the three enzymes which play a key role in this switch, N-acetylglucosaminyltransferases I and II and mannosidase II. (4) The "yellow brick road" which leads from oligomannose to highly branched complex N-glycans with emphasis on the enzymes involved in the process and the factors which control the routes of synthesis. (5) A short discussion of the characteristics of the enzymes involved and of the genes that encode them. (6) The role of complex N-glycans in mammalian and Caenorhabditis elegans development. (7) The crystal structure of N-acetylglucosaminyltransferase I. (8) The discovery of the enzymes which synthesize O-glycan cores 1, 2, 3 and 4 and their elongation.