A Rhizavidin Monomer with Nearly Multimeric Avidin‐Like Binding Stability Against Biotin Conjugates

Developing a monomeric form of an avidin‐like protein with highly stable biotin binding properties has been a major challenge in biotin‐avidin linking technology. Here we report a monomeric avidin‐like protein—enhanced monoavidin—with off‐rates almost comparable to those of multimeric avidin proteins against various biotin conjugates. Enhanced monoavidin (eMA) was developed from naturally dimeric rhizavidin by optimally maintaining protein rigidity during monomerization and additionally shielding the bound biotin by diverse engineering of the surface residues. eMA allowed the monovalent and nonperturbing labeling of head‐group‐biotinylated lipids in bilayer membranes. In addition, we fabricated an unprecedented 24‐meric avidin probe by fusing eMA to a multimeric cage protein. The 24‐meric avidin and eMA were utilized to demonstrate how artificial clustering of cell‐surface proteins greatly enhances the internalization rates of assembled proteins on live cells.     

Fluorescent Silica Nanoparticles with Multivalent Inhibitory Effects towards Carbonic Anhydrases

Multifunctional silica nanoparticles decorated with fluorescent and sulfonamide carbonic anhydrase (CA) inhibitors were prepared and investigated as multivalent enzyme inhibitors against the cytosolic isoforms hCA I and II and the transmembrane tumor‐associated ones hCA IX and XII. Excellent inhibitory effects were observed with these nanoparticles, with K_I values in the low nanomolar range (6.2–0.67 nM ) against all tested isozymes. A significant multivalency effect was seen for the inhibition of the monomeric enzymes hCA I and II compared to the dimeric hCA IX and hCA XII isoforms, where no multivalent effect was observed, suggesting that the multivalent binding is occurring through enzyme clustering.     

Tetra- versus Pentavalent Inhibitors of Cholera Toxin

The five B-subunits (CTB₅) of the Vibrio cholerae (cholera) toxin can bind to the intestinal cell surface so the entire AB₅ toxin can enter the cell. Simultaneous binding can occur on more than one of the monosialotetrahexosylganglioside (GM1) units present on the cell surface. Such simultaneous binding arising from the toxins multivalency is believed to enhance its affinity. Thus, blocking the initial attachment of the toxin to the cell surface using inhibitors with GM1 subunits has the potential to stop the disease. Previously we showed that tetravalent GM1 molecules were sub-nanomolar inhibitors of CTB₅. In this study, we synthesized a pentavalent version and compared the binding and potency of penta- and tetravalent cholera toxin inhibitors, based on the same scaffold, for the first time. The pentavalent geometry did not yield major benefits over the tetravalent species, but it was still a strong inhibitor, and no major steric clashes occurred when binding the toxin. Thus, systems which can adopt more geometries, such as those described here, can be equally potent, and this may possibly be due to their ability to form higher-order structures or simply due to more statistical options for binding.     

Dynamic Expression of DNA Complexation with Self‐assembled Biomolecular Clusters

We report herein the implementation of a dynamic covalent chemistry approach to the generation of multivalent clusters for DNA recognition. We show that biomolecular clusters can be expressed in situ by a programmed self‐assembly process using chemoselective ligations. The cationic clusters are shown, by fluorescence displacement assay, gel electrophoresis and isothermal titration calorimetry, to effectively complex DNA through multivalent interactions. The reversibility of the ligation was exploited to demonstrate that template effects occur, whereby DNA imposes component selection in order to favor the most active DNA‐binding clusters. Furthermore, we show that a chemical effector can be used to trigger DNA release through component exchange reactions.     

Dendrimeric Bisphosphonates for Multivalent Protein Surface Binding

A single weak‐binding event is multiplied into an efficient receptor site for protein surfaces (<10^?1 to >10⁶ M ^?1 in buffered aqueous solution) in a biomimetic fashion. This has hitherto been done with natural host/guest pairs, but not with artificial receptors. The organic reaction presented is one of very few that enable chemists to fuse multiple ionic building blocks covalently in highly polar solution; this one‐pot reaction proceeds with virtually quantitative yield. According to this concept, other building blocks with aldehyde groups can likewise be multiplied into monodisperse functional dendrimers. Small basic proteins are bound by octameric dendrimers in 1:1 or 1:2 complexes with millimolar to submicromolar affinities. The complexation event is studied independently in buffered aqueous solution by three different spectroscopic methods (PFG‐LED, UV/Vis, and fluorescence). Potential new applications include recombinant protein purification through Arg tags on immobilized dendrimers and on/off switching of protein function by reversible active‐site capping of enzymes.