Crystal-state 3D-structural characterization of novel, Aib-based, turn and helical peptides

Relevance of amphiphilicity and helicity on the antibacterial action of a histatin 5-derived peptide

Peptide dhvar4, derived from the active domain of our salivary peptide histatin 5, bears a Phe residue in the middle of its hydrophilic face when folded into an α-helix. We then synthesized an analog with this Phe replaced by Lys and two analogs preserving Phe but bearing two and three α-aminoisobutyric acid (Aib) residues to stabilize the helical structure. The aim of this design was to verify which of the two features is more favorable to the biological activity. We performed a conformational study by means of circular dichroism and nuclear magnetic resonance, made antibacterial tests, and assessed the stability of the peptides in human serum. We observed that amphiphilicity is more important than helix stability, provided a peptide can adopt a helical conformation in a membrane-mimetic environment.

Secondary Structures in Synthetic Poly(Amino Acids): Homo- and Copolymers of Poly(Aib), Poly(Glu), and Poly(Asp)

The secondary structure of poly(amino acids) is an excellent tool for controlling and understanding the functionality and properties of proteins. In this perspective article the secondary structures of the homopolymers of oligo- and poly-glutamic acid (Glu), aspartic acid (Asp), and α-aminoisobutyric acid (Aib) are discussed. Information on external and internal factors, such as the nature of side groups, interactions with solvents and interactions between chains is reviewed. A special focus is directed on the folding in hybrid-polymers consisting of oligo(amino acids) and synthetic polymers. Being part of the SFB TRR 102 "Polymers under multiple constraints: restricted and controlled molecular order and mobility" this overview is embedded into the cross section of protein fibrillation and supramolecular polymers. As polymer- and amino acid folding is an important step for the utilization and design of future biomolecules these principles guide to a deeper understanding of amyloid fibrillation.

Homochiral and heterochiral associations observed in crystals of ArSO2-(Aib)5-OMe

We demonstrated two remarkably different types of network structures that consist of homochiral and heterochiral 1D chains of enantiomeric 3₁₀-helices in the crystals of ArSO2-(Aib)5-OMe.

Participation of non-aminoisobutyric acid (Aib) residues in the 310 helical conformation of Aib-rich foldamers: a solid state study

3₁₀ helical conformations that extend over 21 Å result when selected non-Aib terminal and central residues are incorporated into Aib-rich foldamers.

Conformational preference of 'CαNN' short peptide motif towards recognition of anions

Among several ‘anion binding motifs’, the recently described ‘C^αNN’ motif occurring in the loop regions preceding a helix, is conserved through evolution both in sequence and its conformation. To establish the significance of the conserved sequence and their intrinsic affinity for anions, a series of peptides containing the naturally occurring ‘C^αNN’ motif at the N-terminus of a designed helix, have been modeled and studied in a context free system using computational techniques. Appearance of a single interacting site with negative binding free-energy for both the sulfate and phosphate ions, as evidenced in docking experiments, establishes that the ‘C^αNN’ segment has an intrinsic affinity for anions. Molecular Dynamics (MD) simulation studies reveal that interaction with anion triggers a conformational switch from non-helical to helical state at the ‘C^αNN’ segment, which extends the length of the anchoring-helix by one turn at the N-terminus. Computational experiments substantiate the significance of sequence/structural context and justify the conserved nature of the ‘C^αNN’ sequence for anion recognition through “local” interaction.