2 research outputs found
Versatility of a Glycosylphosphatidylinositol Fragment in Forming Highly Ordered Polymorphs
Glycosylphosphatidylinositols (GPIs)
are often attributed with
the ability to associate with the organized membrane microdomains.
GPI fragment <b>1</b> forms a highly ordered subgel-phase structure
characterized by ordering of both headgroups and alkyl chains in thin
layers. While investigating the driving forces behind the formation
of these ordered monolayers, we have studied polymorphism of <b>1</b> under different conditions employing surface-sensitive X-ray
diffraction methods. Three distinct polymorphs of <b>1</b> (<b>I</b>, <b>II</b>, and <b>III</b>) were identified
and characterized by grazing incidence X-ray diffraction. Polymorphs <b>II</b> (a condensed monolayer structure) and <b>III</b> (highly
ordered subgel phase) coexist on an 8 M urea solution subphase allowing
for a detailed thermodynamic and kinetic analysis of the processes
leading to the formation of these polymorphs. They are enantiotropic
and can be directly interconverted by changes in temperature or lateral
surface pressure. As a consequence, polymorph <b>III</b> nuclei
of critical size (or larger) could be formed by density fluctuations
in a multicomponent system, and they could continue to exist for a
period of time even under conditions that would normally not allow
for the nucleation of polymorph <b>III</b>. The processes described
here could also lead to the formation of patches of highly ordered
structures in a disordered environment of a cell membrane suggesting
that GPIs may play a role in the formation of such domains
Molecular Recognition of Complex-Type Biantennary <i>N</i>‑Glycans by Protein Receptors: a Three-Dimensional View on Epitope Selection by NMR
The current surge in defining glycobiomarkers by applying
lectins
rekindles interest in definition of the sugar-binding sites of lectins
at high resolution. Natural complex-type <i>N</i>-glycans
can present more than one potential binding motif, posing the question
of the actual mode of interaction when interpreting, for example,
lectin array data. By strategically combining <i>N</i>-glycan
preparation with saturation-transfer difference NMR and modeling,
we illustrate that epitope recognition depends on the structural context
of both the sugar and the lectin (here, wheat germ agglutinin and
a single hevein domain) and cannot always be predicted from simplified
model systems studied in the solid state. We also monitor branch-end
substitutions by this strategy and describe a three-dimensional structure
that accounts for the accommodation of the α2,6-sialylated
terminus of a biantennary <i>N</i>-glycan by viscumin. In
addition, we provide a structural
explanation for the role of terminal α2,6-sialylation
in precluding the interaction of natural <i>N</i>-glycans
with lectin from Maackia amurensis.
The approach described is thus capable of pinpointing lectin-binding
motifs in natural <i>N</i>-glycans and providing detailed
structural explanations for lectin selectivity