Oligonucleotide-based systems for input-controlled and non-covalently regulated protein binding

Supramolecular chemists continuously take inspiration from complex biological systems to develop functional molecules involved in molecular recognition and self-assembly. In this regard, ‘smart’ synthetic molecules that emulate allosteric proteins are both exciting and challenging, because many allosteric proteins can be considered as molecular switches that bind to other protein targets in a non-covalent fashion and, importantly, are capable of having their output activity controlled by prior binding to input molecules. This review discusses the foundations and passage towards the development of non-covalently operated oligonucleotide-based systems with protein-binding capacity that can be precisely regulated in an input-controlled manner.     

Multivalent Interactions of Polyamide Based Sequence‐Controlled Glycomacromolecules with Concanavalin A

Binding of mannose presenting macromolecules to the protein receptor concanavalin A (ConA) is investigated by means of single‐molecule atomic force spectroscopy (SMFS) in combination with dynamic light scattering and molecular modeling. Oligomeric (M_w ≈ 1.5–2.5 kDa) and polymeric (M_w ≈ 22–30 kDa) glycomacromolecules with controlled number and positioning of mannose units along the scaffolds accessible by combining solid phase synthesis and thiol–ene coupling are used as model systems to assess the molecular mechanisms that contribute to multivalent ConA–mannose complexes. SMFS measurements show increasing dissociation force from monovalent (≈57 pN) to pentavalent oligomers (≈75 pN) suggesting subsite binding to ConA. Polymeric glycomacromolecules with larger hydrodynamic diameters compared to the binding site spacing of ConA exhibit larger dissociation forces (≈80 pN), indicating simultaneous dissociation from multiple ConA binding sites. Nevertheless, although simultaneous dissociation of multiple ligands could be expected for such multivalent systems, predominantly single dissociation events are observed. This is rationalized by strong coiling of the macromolecules' polyamide backbone due to intramolecular hydrogen bonding hindering unfolding of the coil. Therefore, this study shows that the design of glycopolymers for multivalent receptor binding and clustering must consider 3D structure and intramolecular interactions of the scaffold.     

Gold glyconanoparticles: synthetic polyvalent ligands mimicking glycocalyx-like surfaces as tools for glycobiological studies

A simple and versatile methodology is described for tailoring sugar-functionalised gold nanoclusters (glyconanoparticles) that have 3D polyvalent carbohydrate display and globular shapes. This methodology allows the preparation of glyconanoparticles with biologically significant oligosaccharides as well as with differing carbohydrate density. Fluorescent glyconanoparticles have been also prepared for labelling cells in biological tests. The materials are water soluble, stable under physiological conditions and present an exceptional small core size. All of them have been characterised by (1)H NMR, UV and IR spectroscopy, TEM and elemental analysis. Their highly polyvalent network can mimic glycosphingolipid clustering and interactions at the plasma membrane, providing an controlled system for glycobiological studies. Furthermore, they are useful building blocks for the design of nanomaterials.     

Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands

Multivalent receptor–ligand binding is a key principle in a plethora of biological recognition processes. Immense binding affinities can be achieved with the correct spatial orientation of the ligands. Accordingly, the incorporation of photoswitches, which can be used to reversibly change the spatial orientation of molecules, into multivalent ligands is a means to alter the binding affinity and possibly also the binding mode of such ligands. We report a divalent ligand for the model lectin wheat germ agglutinin (WGA) containing an arylazopyrazole photoswitch. This switch, which has recently been introduced as an alternative to the more commonly used azobenzene moiety, is characterized by almost quantitative E/Z photoswitching in both directions, high quantum yields, and high thermal stability of the Z isomer. The ligand was designed in a way that only one of the isomers is able to bridge adjacent binding sites of WGA leading to a chelating binding mode. Photoswitching induces an unprecedentedly high change in lectin binding affinity as determined by isothermal titration calorimetry (ITC). Furthermore, additional dynamic light scattering (DLS) data suggest that the binding mode of the ligand changes from chelating binding of the E isomer to crosslinking binding of the Z isomer.     

新型臂式氮杂冠醚的合成及其多价螯合的热力学特征

通过采用微波方法提高了1,10-二氧-4,7,13,16-四氮杂18-冠-6 (L1)的合成产率.以该化合物作为母体与溴乙酸乙酯反应合成了两种新型的臂式冠醚L2和L3.采用等温滴定量热法测定了这三种氮杂冠醚与Ca(Ⅱ)键合的热力学参数,量热滴定拟合结果表明,除母体氮杂冠醚外,臂式氮杂冠醚L2和L3均能与Ca(Ⅱ)形成1:1的稳定配合物,其稳定性主要来自于多价螯合的焓贡献.     

Hybrid Multivalent Jack Bean α-Mannosidase Inhibitors: The First Example of Gold Nanoparticles Decorated with Deoxynojirimycin Inhitopes

Among carbohydrate-processing enzymes, Jack bean α-mannosidase (JBα-man) is the glycosidase with the best responsiveness to the multivalent presentation of iminosugar inhitopes. We report, in this work, the preparation of water dispersible gold nanoparticles simultaneously coated with the iminosugar deoxynojirimycin (DNJ) inhitope and simple monosaccharides (β-d-gluco- or α-d-mannosides). The display of DNJ at the gold surface has been modulated (i) by using an amphiphilic linker longer than the aliphatic chain used for the monosaccharides and (ii) by presenting the inhitope, not only in monomeric form, but also in a trimeric fashion through combination of a dendron approach with glyconanotechnology. The latter strategy resulted in a strong enhancement of the inhibitory activity towards JBα-man, with a K_i in the nanomolar range (K_i = 84 nM), i.e., more than three orders of magnitude higher than the monovalent reference compound.