Clay Nanosheet-Based Nanocomposite Supramolecular Hydrogel Enabling Rapid, Reversible Phase Transition Only with Visible Light.

High mechanical properties and rapid sol/gel phase transition are mutually exclusive in the hydrogels reported to date, most likely because the 3D crosslinked networks of mechanically robust hydrogels comprise bundled thick fibers that are not rapidly dissociable or formable. Herein, we report a visible light-responsive hydrogel that showed a rapid, reversible sol/gel phase transition despite its relatively high mechanical properties (storage modulus ~10 Pa). To construct its 3D crosslinked network, we used a design strategy analogous to that employed for our highly water-rich yet mechanically robust nanocomposite supramolecular hydrogel ("aqua material").

Mechanotransducing Hydrogel for Switching Enzyme Reactions through Modulation of Multivalent Salt-Bridge Interactions.

Mechanoresponsive materials can harness mechanical forces to initiate molecular events and alter their physicochemical properties. Enzyme reactions, which enable diverse chemical transformations under mild conditions, have great potential as outputs of the mechanoresponse, especially in biological applications. Here, we present a hydrogel-based platform that realizes mechanotransduction to enzyme reactions through the modulation of multivalent salt-bridge interactions between a polymeric inhibitor incorporated within the gel network and an enzyme in the gel matrix.

ATP-Responsive Nanoparticles Covered with Biomolecular Machine "Chaperonin GroEL".

Herein, we report an ATP-responsive nanoparticle ( NP) whose surface is fully covered with the biomolecular machine "chaperonin protein GroEL". NP was synthesized by DNA hybridization between a gold NP with DNA strands on its surface and GroEL carrying complementary DNA strands at its apical domains. The unique structure of NP was visualized by transmission electron microscopy including under cryogenic conditions.

Reconstitution of microtubule into GTP-responsive nanocapsules.

Nanocapsules that collapse in response to guanosine triphosphate (GTP) have the potential as drug carriers for efficiently curing diseases caused by cancer and RNA viruses because GTP is present at high levels in such diseased cells and tissues. However, known GTP-responsive carriers also respond to adenosine triphosphate (ATP), which is abundant in normal cells as well. Here, we report the elaborate reconstitution of microtubule into a nanocapsule that selectively responds to GTP.

Photoreactive Molecular Glue for Enhancing the Efficacy of DNA Aptamers by Temporary-to-Permanent Conjugation with Target Proteins.

We developed a photoreactive molecular glue, Glue-N, which can provide a universal strategy to enhance the efficacy of DNA aptamers by temporary-to-permanent stepwise stabilization of their conjugates with target proteins. As a proof-of-concept study, we applied Glue-N to the SL1 (DNA aptamer)/c-Met (target protein) conjugate system. Glue-N can adhere to and temporarily stabilize this aptamer/protein conjugate multivalently using its guanidinium ion (Gu) pendants that form a salt bridge with oxyanionic moieties (e.

Bio-adhesive Nanoporous Module: Toward Autonomous Gating.

Here we report a bio-adhesive porous organic module ( COF) composed of hexagonally packed 1D nanopores based on a covalent organic framework. The nanopores are densely decorated with guanidinium ion (Gu ) pendants capable of forming salt bridges with oxyanionic species. COF strongly adheres to biopolymers through multivalent salt-bridging interactions with their ubiquitous oxyanionic species.

Intracellular Photoactivation of Caspase-3 by Molecular Glues for Spatiotemporal Apoptosis Induction.

Caspase-3 (Casp-3) is an enzyme that efficiently induces apoptosis, a form of programmed cell death. We report a dendritic molecular glue Glue that enables intracellular delivery of Casp-3 and its photoactivation. Glue carrying multiple guanidinium (Gu) ion pendants via photocleavable linkages can tightly adhere to Casp-3 and deliver it into the cytoplasm mainly by direct penetration through the plasma membrane.

Asymmetric catalysis mediated by a mirror symmetry-broken helical nanoribbon.

Although chirality has been recognized as an essential entity for life, it still remains a big mystery how the homochirality in nature emerged in essential biomolecules. Certain achiral motifs are known to assemble into chiral nanostructures. In rare cases, their absolute geometries are enantiomerically biased by mirror symmetry breaking.

Molecular Glue that Spatiotemporally Turns on Protein-Protein Interactions.

We developed a dendritic molecular glue Glue-NBD that can serve universally to "turn on" protein-protein interactions (PPIs) spatiotemporally. Glue-NBD carrying multiple guanidinium ion (Gu) pendants can adhere strongly to target proteins and cover their surfaces including the PPI interface regions, thereby suppressing PPIs with their receptor proteins. Upon irradiation with UV light, Glue-NBD on a target protein is photocleaved at butyrate-substituted nitroveratryloxycarbonyl linkages in the dendrimer framework, so that the multivalency for the adhesion is reduced.

Spatiotemporally Controlled Nuclear Translocation of Guests in Living Cells Using Caged Molecular Glues as Photoactivatable Tags.

The cell nucleus is one of the most important organelles as a subcellular drug-delivery target, since modulation of gene replication and expression is effective for treating various diseases. Here, we demonstrate light-triggered nuclear translocation of guests using caged molecular glue (Glue-R) tags, whose multiple guanidinium ion (Gu) pendants are protected by an anionic photocleavable group (butyrate-substituted nitroveratryloxycarbonyl; NVOC). Guests tagged with Glue-R are taken up into living cells via endocytosis and remain in endosomes.

Transferrin-Appended Nanocaplet for Transcellular siRNA Delivery into Deep Tissues.

Transferrin (Tf) is known to induce transcytosis, which is a consecutive endocytosis/exocytosis event. We developed a Tf-appended nanocaplet (NC⊃siRNA) for the purpose of realizing siRNA delivery into deep tissues and RNA interference (RNAi) subsequently. For obtaining NC⊃siRNA, a macromonomer (Gu) bearing multiple guanidinium (Gu) ion units, azide (N) groups, and trityl (Trt)-protected thiol groups in the main chain, side chains, and termini, respectively, was newly designed.

Nitrobenzoxadiazole-Appended Cell Membrane Modifiers for Efficient Optoporation with Noncoherent Light.

NBD-BAM, bearing a nitrobenzoxadiazole (NBD) unit and an oleyl terminus conjugated via a poly(ethylene glycol) (PEG) spacer ( M = 2,000), was designed to fluorescently label cell membranes by docking its hydrophobic oleyl terminus. During laser scanning microscopy in a minimal essential medium (MEM), human hepatocellular carcinoma Hep3B cells labeled with NBD-BAM appeared to undergo optoporation at their plasma membrane. We confirmed this unprecedented possibility by a series of cellular uptake experiments using negatively charged and therefore membrane-impermeable quantum dots (QDs; D = 4.

Caged Molecular Glues as Photoactivatable Tags for Nuclear Translocation of Guests in Living Cells.

We developed dendritic caged molecular glues (Glue-R) as tags for nucleus-targeted drug delivery, whose multiple guanidinium ion (Gu) pendants are protected by an anionic photocleavable unit (butyrate-substituted nitroveratryloxycarbonyl; NVOC). Negatively charged Glue-R hardly binds to anionic biomolecules because of their electrostatic repulsion. However, upon exposure of Glue-R to UV light or near-infrared (NIR) light, the NVOC groups of Glue-R are rapidly detached to yield an uncaged molecular glue (Glue-R) that carries multiple Gu pendants.

Mechanically robust, readily repairable polymers via tailored noncovalent cross-linking.

Expanding the range of healable materials is an important challenge for sustainable societies. Noncrystalline, high-molecular-weight polymers generally form mechanically robust materials, which, however, are difficult to repair once they are fractured. This is because their polymer chains are heavily entangled and diffuse too sluggishly to unite fractured surfaces within reasonable time scales.

Guanidinium-based "molecular glues" for modulation of biomolecular functions.

Molecular adhesion based on multivalent interactions plays essential roles in various biological processes. Hence, "molecular glues" that can adhere to biomolecules may modulate biomolecular functions and therefore can be applied to therapeutics. This tutorial review describes design strategies for developing adhesive motifs for biomolecules based on multivalent interactions.

Adhesive Photoswitch: Selective Photochemical Modulation of Enzymes under Physiological Conditions.

We developed a water-soluble adhesive photoswitch (Glue-Azo-SA, average n = 5) that selectively binds to a target enzyme and photochemically modulates its enzymatic activity even in cell lysates. Its design strategy features a photochromic azobenzene unit (Azo), which carries on one side an inhibitory motif for the target enzyme and on the other a glue part (Glue) that utilizes its multiple guanidinium ion (Gu) pendants for adhering onto the target surface. The target of Glue-Azo-SA is carbonic anhydrase (CA) because sulfonamide (SA) derivatives, such as SA at the terminus of Glue-Azo-SA, are known to bind selectively to the CA active site.

Boronic Acid-Appended Molecular Glues for ATP-Responsive Activity Modulation of Enzymes.

Water-soluble linear polymers GumBAn (m/n = 18/6, 12/12, and 6/18) with multiple guanidinium ion (Gu(+)) and boronic acid (BA) pendants in their side chains were synthesized as ATP-responsive modulators for enzyme activity. GumBAn polymers strongly bind to the phosphate ion (PO4(-)) and 1,2-diol units of ATP via the Gu(+) and BA pendants, respectively. As only the Gu(+) pendants can be used for proteins, GumBAn is able to modulate the activity of enzymes in response to ATP.

Reductively Cleavable Nanocaplets for siRNA Delivery by Template-Assisted Oxidative Polymerization.

A series of water-soluble telechelic dithiol monomers bearing multiple guanidinium ion (Gu(+)) units in their main chains were synthesized for packaging siRNA by template-assisted oxidative polymerization at their thiol termini. In the presence of siRNA, oxidative polymerization of (TEG)Gu4 affords a uniform-sized (7 ± 2 nm) nanocaplet containing siRNA (P(TEG)Gu4⊃siRNA; P(TEG)Gu4 = polymerized (TEG)Gu4). When this small conjugate is incubated with live cells, cellular uptake occurs, and the nanocaplet undergoes depolymerization in the reductive cytosolic environment to liberate the packaged siRNA.

Photoinduced Bioorthogonal 1,3-Dipolar Poly-cycloaddition Promoted by Oxyanionic Substrates for Spatiotemporal Operation of Molecular Glues.

PGlue(PZ), a pyrazoline (PZ)-based fluorescent adhesive which can be generated spatiotemporally in living systems, was developed. Since PGlue(PZ) carries many guanidinium ion (Gu(+)) pendants, it strongly adheres to various oxyanionic substrates through a multivalent salt-bridge interaction. PGlue(PZ) is given by bioorthogonal photopolymerization of a Gu(+)-appended monomer (Glue(TZ)), bearing tetrazole (TZ) and olefinic termini.

Ionic interactions. Subnanoscale hydrophobic modulation of salt bridges in aqueous media.

Polar interactions such as electrostatic forces and hydrogen bonds play an essential role in biological molecular recognition. On a protein surface, polar interactions occur mostly in a hydrophobic environment because nonpolar amino acid residues cover ~75% of the protein surface. We report that ionic interactions on a hydrophobic surface are modulated by their subnanoscale distance to the surface.

Molecular glues for manipulating enzymes: trypsin inhibition by benzamidine-conjugated molecular glues.

Water-soluble bioadhesive polymers bearing multiple guanidinium ion (Gu) pendants at their side-chain termini (Glue -BA, = 10 and 29) that were conjugated with benzamidine (BA) as a trypsin inhibitor were developed. The Glue -BA molecules are supposed to adhere to oxyanionic regions of the trypsin surface, even in buffer, a multivalent Gu/oxyanion salt-bridge interaction, such that their BA group properly blocks the substrate-binding site. In fact, Glue-BA and Glue-BA exhibited 35- and 200-fold higher affinities for trypsin, respectively, than a BA derivative without the glue moiety (TEG-BA).

Structure and shape effects of molecular glue on supramolecular tubulin assemblies.

The possibility to arrange biological molecules into ordered nanostructures is an important issue in nano- and biotechnology. Nature offers a wide range of molecular "bricks" (e.g.

Photoclickable dendritic molecular glue: noncovalent-to-covalent photochemical transformation of protein hybrids.

A water-soluble dendron with a fluorescein isothiocyanate (FITC) fluorescent label and bearing nine pendant guanidinium ion (Gu(+))/benzophenone (BP) pairs at its periphery (Glue(BP)-FITC) serves as a "photoclickable molecular glue". By multivalent salt-bridge formation between Gu(+) ions and oxyanions, Glue(BP)-FITC temporarily adheres to a kinesin/microtubule hybrid. Upon subsequent exposure to UV light, this noncovalent binding is made permanent via a cross-linking reaction mediated by carbon radicals derived from the photoexcited BP units.

Friction-mediated dynamic disordering of phospholipid membrane by mechanical motions of photoresponsive molecular glue: activation of ion permeation.

A water-soluble photoresponsive molecular glue, Azo-(18)Glue, consisting of a photochromic azobenzene core and two adhesive dendritic wedges with a total of 18 peripheral guanidinium ion (Gu(+)) pendants tightly adheres to the surface of a phospholipid membrane, even in buffer, via a multivalent salt-bridge formation with phosphate anions. A photomechanical motion of adhering Azo-(18)Glue possibly gives rise to dynamic structural disordering of the phospholipid membrane and activates transmembrane ion permeation. In sharp contrast, no activation of ion permeation results when poorly adhesive Azo-(6)Glue carrying only six Gu(+) pendants is used in place of Azo-(18)Glue.