Functional Linkers Support Targeting of Multivalent Tweezers to Taspase1.

Taspase 1 is a unique protease not only pivotal for embryonic development but also implicated in leukemias and solid tumors. As such, this enzyme is a promising while still challenging therapeutic target, and with its protein structure featuring a flexible loop preceding the active site a versatile model system for drug development. Supramolecular ligands provide a promising complementary approach to traditional small-molecule inhibitors. Recently, the multivalent arrangement of molecular tweezers allowed the successful targeting of Taspase 1's surface loop. With this study we now want to take the next logic step und utilize functional linker systems that not only allow the implementation of novel properties but also engage in protein surface binding. Consequently, we chose two different linker types differing from the original divalent assembly: a backbone with aggregation-induced emission (AIE) properties to enable monitoring of binding and a calix[4]arene scaffold initially pre-positioning the supramolecular binding units. With a series of four AIE-equipped ligands with stepwise increased valency we demonstrated that the functionalized AIE linkers approach ligand binding affinities in the nanomolar range and allow efficient proteolytic inhibition of Taspase 1. Moreover, implementation of the calix[4]arene backbone further enhanced the ligands' inhibitory potential, pointing to a specific linker contribution.

Multiresponsive hydrogels and organogels based on photocaged cysteine.

Here we present the readily accessible amino acid 4,5-dimethoxy-2-nitrobenzyl-l-cysteine (DNC), as an ultra-low molecular weight gelator (MW = 316 g mol-1). Sonication of DNC in water or organic solvents as well as pH adjustment in water trigger gelation. A diverse set of stimuli (UV irradiation, oxidation, heat or pH change) induce a gel-sol transition. Moreover, the photo-triggered gel-sol transition was used to obtain a controlled cysteine release from the hydrogel.

Heteromultivalent peptide recognition by co-assembly of cyclodextrin and calixarene amphiphiles enables inhibition of amyloid fibrillation.

Heteromultivalency, which involves the simultaneous interactions of more than one type of ligand with more than one type of receptor, is ubiquitous in living systems and provides a powerful strategy to improve the binding efficiency of heterotopic species such as proteins and membranes. However, the design and development of artificial heteromultivalent receptors is still challenging owing to tedious synthesis processes and the need for precise control over the spatial arrangement of the binding sites. Here, we have designed a heteromultivalent platform by co-assembling cyclodextrin and calixarene amphiphiles, so that two orthogonal, non-covalent binding sites are distributed on the surface of the co-assembly. Binding with model peptides shows a synergistic effect of the two receptors, (hetero)multivalency and self-adaptability. The co-assembly shows promise for inhibition of the fibrillation of amyloid-ß peptides and the dissolution of amyloid-ß fibrils, substantially reducing amyloid cytotoxicity. This self-assembled heteromultivalency concept is easily amenable to other ensembles and targets, so that versatile biomedical applications can be envisaged.

Bridging of membrane surfaces by annexin A2.

The protein-mediated formation of membrane contacts is a crucial event in many cellular processes ranging from the establishment of organelle contacts to the docking of vesicles to a target membrane. Annexins are Ca2+ regulated membrane-binding proteins implicated in providing such membrane contacts; however, the molecular basis of membrane bridging by annexins is not fully understood. We addressed this central question using annexin A2 (AnxA2) that functions in secretory vesicle exocytosis possibly by providing membrane bridges. By quantitatively analyzing membrane contact formation using a novel assay based on quartz crystal microbalance recordings, we show that monomeric AnxA2 can bridge membrane surfaces Ca2+ dependently. However, this activity depends on an oxidative crosslink involving a cysteine residue in the N-terminal domain and thus formation of disulfide-linked dimers. Alkylated AnxA2 in which this cysteine residue has been modified and AnxA2 mutants lacking the N-terminal domain are not capable of bridging membrane surfaces. In contrast, a heterotetrameric complex comprising two membrane binding AnxA2 subunits linked by a S100A10 dimer can provide membrane contacts irrespective of oxidation status. Thus, monomeric AnxA2 only contains one lipid binding site and AnxA2-mediated linking of membrane surfaces under non-oxidative intracellular conditions most likely requires AnxA2-S100 complex formation.

Writing with molecules on molecular printboards.

Nanotechnology aspires to create functional materials with characteristic dimensions of the order 1-100 nm. One requirement to make nanotechnology work is to precisely position molecules and nanoparticles on surfaces, so that they may be addressed and manipulated for bottom-up construction of nanoscale devices. Here we review the concept of a "molecular printboard". A molecular printboard is a monolayer of host molecules on a solid substrate on which guest molecules can be attached with control over position, binding strength, and binding dynamics. To this end, cyclodextrins were immobilized in monomolecular layers on gold, on silicon wafers and on glass. Guest molecules (for example, adamantane and ferrocene derivatives) bind to these host surfaces through supramolecular, hydrophobic inclusion interaction. Multivalent interactions are exploited to tune the binding strength and dynamics of the interaction of guest molecules with the printboard. Molecules can be positioned onto the printboard using supramolecular microcontact printing and supramolecular dip-pen nanolithography due to the specific interaction between the 'ink' and the substrate. In this way, nanoscale patterns can be written and erased on the printboard. Currently, the molecular printboard is exploited for nanofabrication, for example in combination with electroless deposition of metals and by means of supramolecular layer-by-layer deposition.