2 research outputs found
Chemical Synthesis Demonstrates That Dynamic O‑Glycosylation Regulates the Folding and Functional Conformation of a Pivotal EGF12 Domain of the Human NOTCH1 Receptor
The interaction of
the human NOTCH1 receptor and its ligands is
a crucial step in initiating the intracellular signal transductions,
in which O-glycosylation of the extracellular EGF-like domain strongly
affects multiple aspects of cell differentiation, development, and
cancer biology. However, consequences of biosynthetic O-glycosylation
processes in the endoplasmic reticulum (ER) and Golgi on the folding
of EGF domains remain unclear. Synthetic human NOTCH1 EGF12 modules
allow for new insight into the crucial roles of O-glycosylation in
the folding and conformation of this pivotal domain. Here, we show
for the first time that predominant O-glucosylation at Ser458 facilitates
proper folding of the EGF12 domain in the presence of calcium ion,
while the nonglycosylated linear EGF12 peptide affords large amounts
of misfolded products (>50%) during <i>in vitro</i> oxidative
folding. Strikingly, O-fucosylation at Thr466 prior to O-glucosylation
at Ser458 totally impedes folding of EGF12 independent of calcium
ion, whereas modification of the Fucα1→ moiety with β-linked
GlcNAc dramatically enhances folding efficiency. In addition, we elicit
that extension of the Glcβ1→ moiety with xyloses is a
negative-regulation mechanism in the folding of EGF12 when synthesis
of a trisaccharide (Xylα1→3ÂXylα1→3ÂGlcβ1→)
dominates over the posttranslational modification at Thr466. Comprehensive
nuclear magnetic resonance studies of correctly folded EGF12 modules
demonstrate that noncovalently bonded bridges between sugars and peptide
moieties, namely sugar bridges, contribute independently to the stabilization
of the antiparallel β-sheet in the ligand-binding region. Our
results provide evidence that the dynamic O-glycosylation status of
the EGF12 domain elaborated in the ER and Golgi strongly affects folding
and trafficking of the human NOTCH1 receptor
Convergent Solid-Phase Synthesis of Macromolecular MUC1 Models Truly Mimicking Serum Glycoprotein Biomarkers of Interstitial Lung Diseases
Synthetic macromolecular MUC1 glycopeptides
have been used to unravel molecular mechanisms in antibody recognition
of disease-specific epitopes. We have established a novel synthetic
strategy for MUC1 tandem repeats having complex O-glycosylation states
at each repeating unit based on convergent solid-phase fragment condensation
under microwave irradiation. We have accomplished the synthesis of
77 amino acid MUC1 glycopeptides (MW = 12 759) having three
major antigenic O-glycoforms [Tn, core 1 (T), and core 2 structures]
at 10 designated positions out of 19 potential O-glycosylation sites.
We demonstrate that the macromolecular MUC1 glycopeptide displaying
the essential glycopeptidic neoepitope Pro-Asp-ThrÂ(sialyl-T)-Arg-Pro-Ala-Pro
at two different tandem repeats is an excellent serum MUC1 model showing
ideal stoichiometric binding with anti-KL6/MUC1 antibody in the sandwich
ELISA to quantify human serum KL6/MUC1 levels as a critical biomarker
of interstitial lung diseases