Peptidosteroid Tweezers Revisited: DNA Binding Through an Optimised Design

Untapped Opportunities of Resin-to-Resin Transfer Reactions (RRTR) for the Convergent Assembly of Multivalent Peptide Conjugates

Handling of the individual fragments remains a bottleneck in the convergent assembly of peptides. Overlooked since the emergence of ligation chemistries during the past two decades, so-called resin-to-resin transfer reactions (RRTR) are here described as a strategic shortcut in this context. Condensation of the involved moieties at an acceptor resin is facilitated by shuttling peptide segments directly from a donor resin in a one-pot fashion. The straightforward synthesis of a sterically constrained 13-mer peptidosteroid model illustrates the utility of this approach, presenting the first successful application of the RRTR methodology in the field of multivalent design and bioconjugation. Relying on established procedures to generate, monitor and isolate intermediates and products, the solid-phase nature of the entire strategy allows for the fast construction of polypeptide adducts and libraries thereof. As such, a rejuvenated use and new opportunities for RRTR are reported.

Intracellular Reactions Promoted by Bis(histidine) Miniproteins Stapled Using Palladium(II) Complexes

The generation of catalytically active metalloproteins inside living mammalian cells is a major research challenge at the interface between catalysis and cell biology. Herein we demonstrate that basic domains of bZIP transcription factors, mutated to include two histidine residues at i and i+4 positions, react with palladium(II) sources to generate catalytically active, stapled pallado-miniproteins. The resulting constrained peptides are efficiently internalized into living mammalian cells, where they perform palladium-promoted depropargylation reactions without cellular fixation. Control experiments confirm the requirement of the peptide scaffolding and the palladium staple for attaining the intracellular reactivity.

Specific dsDNA recognition by a mimic of the DNA binding domain of the c-Myc/Max transcription factor

We here report on the synthesis of the first mimic of the DNA binding domain of the c-Myc/Max-bHLH-ZIP transcription factor able to selectively recognize its cognate E-box sequence 5'-CACGTG-3' through the major groove of the double-stranded DNA. The designed peptidosteroid conjugate was shown to be effective as DNA binder in the presence of excess competitor DNA.

Metal-Dependent DNA Recognition and Cell Internalization of Designed, Basic Peptides

A fragment of the DNA basic region (br) of the GCN4 bZIP transcription factor has been modified to include two His residues at designed i and i+4 positions of its N-terminus. The resulting monomeric peptide (brHis2) does not bind to its consensus target DNA site (5'-GTCAT-3'). However, addition of Pd(en)Cl2 (en, ethylenediamine) promotes a high-affinity interaction with exquisite selectivity for this sequence. The peptide-DNA complex is disassembled by addition of a slight excess of a palladium chelator, and the interaction can be reversibly switched multiple times by playing with controlled amounts of either the metal complex or the chelator. Importantly, while the peptide brHis2 fails to translocate across cell membranes on its own, addition of the palladium reagent induces an efficient cell internalization of this peptide. In short, we report (1) a designed, short peptide that displays highly selective, major groove DNA binding, (2) a reversible, metal-dependent DNA interaction, and (3) a metal-promoted cell internalization of this basic peptide.

Sequence-selective DNA recognition and enhanced cellular up-take by peptide-steroid conjugates

Several GCN4 bZIP TF models have previously been designed and synthesized. However, the synthetic routes towards these constructs are typically tedious and difficult. We here describe the substitution of the Leucine zipper domain of the protein by a deoxycholic acid derivative appending the two GCN4 binding region peptides through an optimized double azide-alkyne cycloaddition click reaction. In addition to achieving sequence specific dsDNA binding, we have investigated the potential of these compounds to enter cells. Confocal microscopy and flow cytometry show the beneficial influence of the steroid on cell uptake. This unique synthetic model of the bZIP TF thus combines sequence specific dsDNA binding properties with enhanced cell-uptake. Given the unique properties of deoxycholic acid and the convergent nature of the synthesis, we believe this work represents a key achievement in the field of TF mimicry.

A designed DNA binding motif that recognizes extended sites and spans two adjacent major grooves

We report the rational design of a DNA-binding peptide construct composed of the DNA-contacting regions of two transcription factors (GCN4 and GAGA) linked through an AT-hook DNA anchor. The resulting chimera, which represents a new, non-natural DNA binding motif, binds with high affinity and selectivity to a long composite sequence of 13 base pairs (TCAT-AATT-GAGAG).

Cyclodextrin-peptide conjugates for sequence specific DNA binding

Synthetic models of bZIP transcription factors have been developed with the capability of specific DNA recognition. Our design is based on the CuAAC mediated conjugation of basic region Leucine Zipper peptides to different derivatives of α, β and γ-cyclodextrins equipped with azide functionalities. Thorough optimization of reaction conditions allowed convergent and simultaneous conjugation of two long unprotected cationic peptides to cyclodextrin-bis azide derivatives. The resulting constructs were shown to specifically recognize their cognate DNA sequence with nM affinities. In comparison with previously developed TF models, the derivatives described here combine the enhanced DNA binding capabilities with an easy and convergent synthetic route.

Stapling monomeric GCN4 peptides allows for DNA binding and enhanced cellular uptake

Facile synthesis of DNA binding stapled peptides which show enhanced cellular uptake is described considering the GCN4 transcription factor as a model protein.