Mechanical properties of single double-stranded DNA (dsDNA) in the presence of different binding ligands were analyzed in optical-tweezers experiments with subpiconewton force resolution. The binding of ligands to DNA changes the overall mechanic response of the dsDNA molecule. This fundamental property can be used for discrimination and identification of different binding modes and, furthermore, may be relevant for various processes like nucleosome packing or applications like cancer therapy. We compared the effects of the minor groove binder distamycin-A, a major groove binding alpha-helical peptide, the intercalators ethidium bromide, YO-1, and daunomycin as well as the bisintercalator YOYO-1 on lambda-DNA. Binding of molecules to the minor and major groove of dsDNA induces distinct changes in the molecular elasticity compared to the free dsDNA detectable as a shift of the overstretching transition to higher forces. Intercalating molecules affect the molecular mechanics by a complete disappearance of the B-S transition and an associated increase in molecular contour length. Significant force hysteresis effects occurring during stretching/relaxation cycles with velocities>10 nm/s for YOYO-1 and >1000 nm/s for daunomycin. These indicate structural changes in the timescale of minutes for the YOYO-DNA and of seconds for the daunomycin-DNA complexes, respectively.

Changes in the elastic properties of single deoxyribonucleic acid (DNA) molecules in the presence of different DNA-binding agents are identified using atomic force microscope single molecule force spectroscopy. We investigated the binding of poly(dG-dC) dsDNA with the minor groove binder distamycin A, two supposed major groove binders, an alpha-helical and a 3(10)-helical peptide, the intercalants daunomycin, ethidium bromide and YO, and the bis-intercalant YOYO. Characteristic mechanical fingerprints in the overstretching behavior of the studied single DNA-ligand complexes were observed allowing the distinction between different binding modes. Docking of ligands to the minor or major groove of DNA has the effect that the intramolecular B-S transition remains visible as a distinct plateau in the force-extension trace. By contrast, intercalation of small molecules into the double helix is characterized by the vanishing of the B-S plateau. These findings lead to the conclusion that atomic force microscope force spectroscopy can be regarded as a single molecule biosensor and is a potent tool for the characterization of binding motives of small ligands to DNA.

Gene expression in eukaryotes is controlled at the transcriptional level by the specific binding of transcription factors to defined DNA sequences. In this way, cell growth, differentiation, and development are regulated. The possibility to influence and control cell metabolism through modified synthetic transcription factors [1][2][3][4] offers fascinating prospects for molecular cell biology in the framework of biomimetics and synthetic biology. [5,6] The design and synthesis of biologically active artificial enzymes and new protein-based materials can be investigated by the combination of bioorganic bottom-up synthesis and single-molecule affinity nanotechnology. With this approach important questions can be addressed, such as the extent to which a single recognition helix contributes to the specific binding of a complete protein to DNA, the effect that a single amino acid point mutation has upon biological specificity and affinity, and the minimal peptide sequence length to ensure binding specificity. This approach would also aid in the design of artificial proteins that contain a purely synthetic helix-turn-helix (HTH) binding motif.In this context, it is of considerable interest to elucidate the DNA-binding specificity of synthetic peptides with a primary sequence akin to the binding domain of a transcription factor. We studied a 20-residue peptide that represents the native sequence of a binding epitope of the transcription activator PhoB (E. coli) and three single point mutants of this peptide.PhoB is a transcription activator which, after phosphorylation by PhoR, binds to the phosphate box in the promoter region of the phosphate regulon pho and activates the expression of genes involved in phosphate metabolism.

Recent developments in single molecule force spectroscopy (SMFS) allow direct observation and measurements of forces that hold protein-DNA complexes together. Furthermore, the mechanics of double-stranded (ds) DNA molecules in the presence of small binding ligands can be detected. The results elucidate molecular binding mechanisms and open the way for ultra sensitive and powerful biosensor applications.

Synthetically challenging, the efrapeptins are a class of peptide antibiotics rich in α,α‐dialkylated amino acids. Efrapeptin C (see picture) was synthesized for the first time by a combination of solution‐phase and solid‐phase peptide synthesis steps with segment condensations.