Impact of Peptide Sequences on Their Structure and Function: Mimicking of Virus-Like Nanoparticles for Nucleic Acid Delivery.

We rationally designed a series of amphiphilic hepta-peptides enriched with a chemically conjugated guanidiniocarbonylpyrrole (GCP) unit at the lysine side chain. All peptides are composed of polar (GCP) and non-polar (cyclohexyl alanine) residues but differ in their sequence periodicity, resulting in different secondary as well as supramolecular structures. CD spectra revealed the assembly of ß-sheet-, α-helical and random structures for peptides 1, 2 and 3, respectively. Consequently, this enabled the formation of distinct supramolecular assemblies such as fibres, nanorod-like or spherical aggregates. Notably, all three cationic peptides are equipped with the anion-binding GCP unit and thus possess a nucleic acid-binding centre. However, only the helical (2) and the unstructured (3) peptide were able to assemble into small virus-like DNA-polyplexes and effectively deliver DNA into cells. Notably, as both peptides (2 and 3) were also capable of siRNA-delivery, they could be utilized to downregulate expression of the caner-relevant protein Survivin.

pH-Controlled Formation of a Stable ß-Sheet and Amyloid-like Fibers from an Amphiphilic Peptide: The Importance of a Tailor-Made Binding Motif for Secondary Structure Formation.

The new amphiphilic peptide 1 is composed of alternating cyclohexyl side chains and guanidiniocarbonyl pyrrole (GCP) groups. In contrast to analogue 2, which contains lysine instead of the GCP groups and only exists as a random coil owing to charge repulsion, peptide 1 forms a stable ß-sheet at neutral pH in aqueous medium. The weakly basic GCP groups (pKa ≈7) are key for secondary structure formation as they stabilize the ß-sheet through mutual interactions (formation of a "GCP zipper"). The ß-sheets further aggregate into left-handed helically twisted fibers. However, ß-sheet formation is completely reversible as a function of pH. At low pH (ca. 4), peptide 1 is unstructured (random coil) as all GCP units are protonated. Only round colloidal particles are observed. The amyloid nature of the fibers formed at neutral pH was confirmed by staining experiments with Congo Red and thioflavin T. Furthermore, at millimolar concentrations, peptide 1 forms a stable hydrogel.

Guanidiniocarbonyl pyrrole (GCP) conjugated PAMAM-G2, a highly efficient vector for gene delivery: the importance of DNA condensation.

A novel hybrid compound 1 efficiently shuttles genetic material into HeLa cells at concentrations as low as 0.6 µM, whereas the parent compound PAMAM-G2 is ineffective even at 200 µM. The high efficiency of 1 stems from its capabiliy to form highly condensed ligand-DNA polyplexes. Its binding affinity is actually lower than for the parent dendrimer. Compound 1 is even 200 times more effective and less cytotoxic than PEI, the current gold standard in gene transfection with cationic polymers.

Supramolecular double helix from capped γ-peptide.

The single crystal X-ray diffraction study of capped γ-peptide reveal that the peptide adopts helical conformation which self-assemble to form a supramolecular parallel double helical structure using intermolecular hydrogen bonding as well as π-π stacking interactions in the solid state.

Fabrication of hollow self-assembled peptide microvesicles and transition from sphere-to-rod structure.

This paper presents the construction of hollow peptide microspheres and the mechanism of transition of microspheres to rod-like vesicles at low concentration. The tripeptides Boc-Phe-Maba-Phe-OMe 1 and Boc-Phe-Maba-Tyr-OMe 2, each of them containing a rigid m-aminobenzoic acid (Maba) template at the central position, forms microspheres at a concentration of 1.6 mM in methanol. At low concentration, these vesicular structures are fused through neck formation, and this leads to sphere-to-rod transition of vesicles. Sizes of these microspheres increase with increasing concentration. We have successfully characterized this transition by fluorescence spectroscopy, DLS, and electron microscopic study. The scanning electron microscopy clearly shows that these spheres are hollow. One important property of these microvesicular structures is the encapsulation of a potent anticonvulsant and mood stabilizing drug carbamazepine, which holds future promise to use these microvesicles as delivery vehicles.