3 research outputs found
Specific Adhesion of Carbohydrate Hydrogel Particles in Competition with Multivalent Inhibitors Evaluated by AFM
Synthetic
glycooligomers have emerged as valuable analogues for
multivalent glycan structures in nature. These multivalent carbohydrates
bind to specific receptors and play a key role in biological processes.
In this work, we investigate the specific interaction between mannose
ligand presenting soft colloidal probes (SCPs) attached to an atomic
force microscope (AFM) cantilever and a Concanavalin A (ConA) receptor
surface in the presence of competing glycooligomer ligands. We studied
the SCP–ConA adhesion energy via the JKR approach and AFM pull-off
experiments in combination with optical microscopy allowing for simultaneous
determination of the contact area between SCP and ConA surface. We
varied the contact time, loading rate and loading force and measured
the resulting mannose/ConA interaction. The average adhesion energy
per mannose ligand on the probe was 5 kJ/mol, suggesting that a fraction
of mannose ligands presented on the SCP bound to the receptor surface.
Adhesion measurements via competitive binding of the SCP in the presence
of multivalent glycooligomer ligands did not indicate an influence
of their multivalency on the glycooligomer displacement from the ConA
surface. The absence of this “multivalency effect” indicates
that glycooligomers and ConA do not associate via chelate complexes
and shows that steric shielding by the glycooligomers does not slow
their displacement upon competitive binding of a ligand presenting
surface. These results highlight the high reversibility of carbohydrate–surface
interactions, which could be an essential feature of recognition processes
on the cell surface
Metal-Mediated Molecular Self-Healing in Histidine-Rich Mussel Peptides
Mussels withstand high-energy wave
impacts in rocky seashore habitats
by fastening tightly to surfaces with tough and self-healing proteinaceous
fibers called byssal threads. Thread mechanical behavior is believed
to arise from reversibly breakable metal coordination cross-links
embedded in histidine-rich protein domains (HRDs) in the principle
load-bearing proteins comprising the fibrous thread core. In order
to investigate HRD behavior at the molecular level, we have synthesized
a histidine-rich peptide derived from mussel proteins (His<sub>5</sub>-bys) and studied its reversible adhesive self-interaction in the
presence and absence of metal ions using PEG-based soft-colloidal
probes (SCPs). Adhesion energies of greater than 0.3 mJ/m<sup>2</sup> were measured in the presence of metal ions, and the stiffness of
the modified SCPs exhibited a 3-fold increase, whereas no adhesion
was observed in the absence of metals. Raman spectroscopy confirmed
the presence of metal-coordination via histidine residues by the peptide–supporting
the role of His-metal complexes in the mechanical behavior of the
byssus
Carbohydrate-Lectin Recognition of Sequence-Defined Heteromultivalent Glycooligomers
Multivalency as a key principle in
nature has been successfully
adopted for the design and synthesis of artificial glycoligands by
attaching multiple copies of monosaccharides to a synthetic scaffold.
Besides their potential in various applied areas, e.g. as antiviral
drugs, for the vaccine development and as novel biosensors, such glycomimetics
also allow for a deeper understanding of the fundamental aspects of
multivalent binding of both artificial and natural ligands. However,
most glycomimetics so far neglect the purposeful arranged heterogeneity
of their natural counterparts, thus limiting more detailed insights
into the design and synthesis of novel glycomimetics. Therefore, this
work presents the synthesis of monodisperse glycooligomers carrying
different sugar ligands at well-defined positions along the backbone
using for the first time sequential click chemistry and stepwise assembly
of functional building blocks on solid support. This approach allows
for straightforward access to sequence-defined, multivalent glycooligomers
with full control over number, spacing, position, and type of sugar
ligand. We demonstrate the synthesis of a set of heteromultivalent
oligomers presenting mannose, galactose, and glucose residues. All
heteromultivalent structures show surprisingly high affinities toward
Concanavalin A lectin receptor in comparison to their homomultivalent
analogues presenting the same number of binding ligands. Detailed
studies of the ligand/receptor interaction using STD-NMR and 2fFCS
indeed indicate a change in binding mechanism for trivalent glycooligomers
presenting mannose or combinations of mannose and galactose residues.
We find that galactose residues do not participate in the binding
to the receptor, but they promote steric shielding of the heteromultivalent
glycoligands and thus result in an overall increase in affinity. Furthermore,
the introduction of nonbinding ligands seems to suppress receptor
clustering of multivalent ligands. Overall these results support the
importance of heteromultivalency specifically for the design of novel
glycoligands and help to promote a fundamental understanding of multivalent
binding modes