Bioorganic & Medicinal Chemistry Letters
Synthesis of N-glycan units for assessment of substrate structural
requirements of N-acetylglucosaminyltransferase III
Shinya Hanashima a,b, Hiroaki Korekane c, Naoyuki Taniguchi c, Yoshiki Yamaguchi a,
⇑
a Structural Glycobiology Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center for Systems Chemical Biology, RIKEN Global Research Cluster,
Wako, Saitama 351-0198, Japan
b Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
c Disease Glycomics Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center for Systems Chemical Biology, RIKEN Global Research Cluster, Wako,
Saitama 351-0198, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
N-Acetylglucosaminyltransferase (GnT) III is a glycosyltransferase which produces bisected N-glycans by
transferring GlcNAc to the 4-position of core mannose. Bisected N-glycans are involved in physiological
and pathological processes through the functional regulation of their carrier proteins. An understanding
of the biological functions of bisected glycans will be greatly accelerated by use of specific inhibitors of
GnT-III. Thus far, however, such inhibitors have not been developed and even the substrate-binding mode
of GnT-III is not fully understood. To gain insight into structural features required of the substrate, we
systematically synthesized four N-glycan units, the branching parts of the bisected and non-bisected
N-glycans. The series of syntheses were achieved from a common core trimannose, giving bisected tetra-
and hexasaccharides as well as non-bisected tri- and pentasaccharides. A competitive GnT-III inhibition
assay using the synthetic substrates revealed a vital role for the Manb(1–4)GlcNAc moiety. In keeping
Received 3 June 2014
Revised 22 July 2014
Accepted 29 July 2014
Available online 6 August 2014
Keywords:
Bisecting GlcNAc
N-Glycan
Synthesis
Glycosylation
with previous reports, GlcNAc at the
a1,3-branch is also involved in the interaction. The structural
N-Acetylglucosaminyltransferase III
requirements of GnT-III elucidated in this study will provide a basis for rational inhibitor design.
Ó 2014 Elsevier Ltd. All rights reserved.
Protein N-glycosylation takes place in the endoplasmic reticu-
lum (ER) and influences many of characteristics and functions of
glycoproteins including folding and degradation,1 trafficking,2
and cell adhesion.3 Throughout the glycan processing pathway,
one of the important modifications is the introduction of the
bisecting N-acetylglucosamine (GlcNAc) residue. N-acetylglucos-
aminyltransferase (GnT) III is responsible for inserting bisecting
GlcNAc at O4 of the core b-mannose via a b-linkage, using
UDP-GlcNAc as donor substrate.4 In general, it is thought that the
bisecting GlcNAc is not further glycosylated under physiological
conditions, which is in sharp contrast to the GlcNAc at the mannos-
es on both 1–3 and 1–6 branches.
Accumulating evidence suggests that bisecting GlcNAc regu-
lates tumor progression and migration, and Alzheimer’s disease.
Bisecting GlcNAc suppresses tumor progression by an effect on
growth factor signaling5 induced through galectin-mediated cross-
linking.6 Cell adhesion molecules with bisecting GlcNAc on their
N-glycans, particularly with respect to E-cadherin and integrins,
retard tumor migration.7–9 The mechanism of action may be due
to the fact that the bisected N-glycan is a poor acceptor for
GnT-V thereby arresting the formation of migration-related hyper
branched N-glycans.10,11 Bisecting GlcNAc is also involved in
Alzheimer’s disease, altering both the clearance and production
of amyloid-b.12,13 It also plays a pivotal role in suppression of
N-glycan branching, that is, inhibition of b1,6-GlcNAc transfer by
GnT-V and of core fucosylation by Fut8.14–16
Despite the synthetic challenge and because of its importance in
cellular events, the chemical synthesis of N-glycans with bisecting
GlcNAc has now been successfully achieved.17–21 One example of
an answer to overcoming some of the difficulties in the synthesis
has been to couple bisecting GlcNAc before the introduction of
the 1,3 and 1,6-branch mannose to avoid steric hindrance.
‘Designed’ bisected glycans through synthetic approaches are of
great importance for analyses of structure, dynamics and interac-
tions. The synthetic bisected hexasaccharide 1 has been used as a
ligand for mouse dendritic cell inhibitory receptor 2 (DCIR2),
which allowed the ligand recognition mode of DCIR2 to be revealed
by X-ray crystallography and NMR.22 Crystallographic analysis of a
legume lectin PHA-E, which is widely used for detection of bisected
glycans, was assisted using chemically synthesized ligands 1.23,24
The substrate specificity of GnT-III has been studied using trun-
cated substrates at the non-reducing terminus.25 GnT-III requires a
⇑
Corresponding author. Tel.: +81 48 467 9619; fax: +81 48 467 9620.
b-GlcNAc residue on the
a1,3-Man which is transferred by GnT-I,
0960-894X/Ó 2014 Elsevier Ltd. All rights reserved.