3 research outputs found
Stabilizing Impact of N‑Glycosylation on the WW Domain Depends Strongly on the Asn-GlcNAc Linkage
N-glycans
play important roles in many cellular processes and can
increase protein conformational stability in specific structural contexts.
Glycosylation (with a single GlcNAc) of the reverse turn sequence
Phe-Yyy-Asn-Xxx-Thr at Asn stabilizes the Pin 1 WW domain by −0.85
± 0.12 kcal mol<sup>–1</sup>. Alternative methods exist
for attaching carbohydrates to proteins; some occur naturally (e.g.,
the O-linkage), whereas others use chemoselective ligation reactions
to mimic the natural N- or O-linkages. Here, we assess the energetic
consequences of replacing the Asn linkage in the glycosylated WW domain
with a Gln linkage, with two natural O-linkages, with two unnatural
triazole linkages, and with an unnatural α-mercaptoacetamide
linkage. Of these alternatives, only glycosylation of the triazole
linkages stabilizes WW, and by a smaller amount than N-glycosylation,
highlighting the need for caution when using triazole- or α-mercaptoacetamide-linked
carbohydrates to mimic native N-glycans, especially where the impact
of glycosylation on protein conformational stability is important
Structural and Energetic Basis of Carbohydrate–Aromatic Packing Interactions in Proteins
Carbohydrate–aromatic interactions
mediate many biological
processes. However, the structure–energy relationships underpinning
direct carbohydrate–aromatic packing interactions in aqueous
solution have been difficult to assess experimentally and remain elusive.
Here, we determine the structures and folding energetics of chemically
synthesized glycoproteins to quantify the contributions of the hydrophobic
effect and CH−π interactions to carbohydrate–aromatic
packing interactions in proteins. We find that the hydrophobic effect
contributes significantly to protein–carbohydrate interactions.
Interactions between carbohydrates and aromatic amino acid side chains,
however, are supplemented by CH−π interactions. The strengths
of experimentally determined carbohydrate CH−π interactions
do not correlate with the electrostatic properties of the involved
aromatic residues, suggesting that the electrostatic component of
CH−π interactions in aqueous solution is small. Thus,
tight binding of carbohydrates and aromatic residues is driven by
the hydrophobic effect and CH−π interactions featuring
a dominating dispersive component
Iminosugar C‑Glycoside Analogues of α‑d‑GlcNAc-1-Phosphate: Synthesis and Bacterial Transglycosylase Inhibition
We
herein describe the first synthesis of iminosugar C-glycosides
of α-d-GlcNAc-1-phosphate in 10 steps starting from
unprotected d-GlcNAc. A diastereoselective intramolecular
iodoamination–cyclization as the key step was employed to construct
the central piperidine ring of the iminosugar and the C-glycosidic
structure of α-d-GlcNAc. Finally, the iminosugar phosphonate
and its elongated phosphate analogue were accessed. These phosphorus-containing
iminosugars were coupled efficiently with lipophilic monophosphates
to give lipid-linked pyrophosphate derivatives, which are lipid II
mimetics endowed with potent inhibitory properties toward bacterial
transglycosylases (TGase)