A Selective Cucurbit[8]uril-Peptide Beacon Ensemble for the Ratiometric Fluorescence Detection of Peptides

A convenient supramolecular strategy for constructing a ratiometric fluorescent chemosensing ensemble, consisting of a macrocyclic host (cucurbit[8]uril CB[8]), and a pyrene-tagged amphiphilic peptide beacon (AP 1), is reported. AP 1 unfolds upon encapsulation of the pyrene termini into the hydrophobic CB[8] cavity. This changes pyrene excimer to monomer emission. Substrates with higher affinity for the CB[8] cavity can displace AP 1 from the ensemble. The released AP 1 folds again to form a pyrene excimer, which allows for the ratiometric fluorescence monitoring of the substrate. In this report, the ensemble capacity for ratiometric fluorescence monitoring of biological substrates, such as amino acid derivatives, specific peptides, and proteins, in aqueous media is demonstrated.

Multivalent Ligands with Tailor-Made Anion Binding Motif as Stabilizers of Protein-Protein Interactions

Modulation of protein-protein interactions (PPIs) is essential for understanding and tuning biologically relevant processes. Although inhibitors for PPIs are widely used, the field still lacks the targeted design of stabilizers. Here, we report unnatural stabilizers based on the combination of multivalency effects and the artificial building block guanidiniocarbonylpyrrol (GCP), an arginine mimetic. Unlike other GCP-based ligands that modulate PPIs in different protein targets, only a tetrameric design shows potent activity as stabilizer of the 14-3-3ζ/C-Raf and 14-3-3ζ/Tau complexes in the low-micromolar range. This evidences the role of multivalency for achieving higher specificity in the modulation of PPIs.

Peptide-Based Probes with an Artificial Anion-Binding Motif for Direct Fluorescence "Switch-On" Detection of Nucleic Acid in Cells

This work reports two new peptide-based fluorescence probes (1 and 2) for the detection of ds-DNA at physiological pH. Probes 1 and 2 contain a fluorophore, either amino-naphthalimide or diethyl-aminocoumarin, respectively, and two identical peptide arms each equipped with a guanidiniocarbonylpyrrole (GCP) anion-binding motif. These probes show "switch-on" fluorescence response upon binding to ds-DNA, whereby they can differentiate between various types of polynucleotides. For instance, they exhibit more pronounced fluorescence response for AT-rich polynucleotides than GC-rich polynucleotides, and both give only negligible response to ds-RNA. The fluorimetric response of 1 is proportional to the AT-basepair content in DNA, whereas the fluorescence of 2 is sensitive to the secondary structure of the polynucleotide. Fluorescence experiments, thermal melting experiments and circular dichroism studies suggest that 1 interacts with ds-DNA in a combined intercalation and minor groove binding, whereas 2 interacts mainly with the outer surface of DNA/RNA. As 1 and 2 have a very low cytotoxicity, 1 can be applied for the imaging of nuclear DNA in cells.