Design, Construction, and Conformational Analysis of gamma Peptide Double Helices

Abstract

The double helix is the most common and very important structural motif in nucleic acids. In comparison, double helix motifs are rare in proteins and other biomolecules. Nevertheless, gramicidins A-D and feglymicin, linear natural polypeptides with alternating amino acid configuration, produced by Bacillus brevis have been shown to adopt double helix conformation. In addition, synthetic peptides with alternating αL and αD amino acids have also been shown to adopt double helix structures. These double helical structures of αL, αD -peptides are of particular interest because of their ability to form transmembrane channels. Extensive efforts have been made over the decades to design β-double helix structures from different building blocks. Besides the alternating αL and αD peptides, aromatic oligoamides and the aromatic building blocks capable of metal coordination have been used to construct double helices. Recently, we demonstrated the double helical structures from the homooligomers of achiral (E)-α,β-unsaturated 4, 4-dialkyl substituted -amino acids. In continuation, we sought to investigate the design of chiral double helices, the ability of the double helices to accommodate other than the (E)-α,β-unsaturated 4, 4-dialkyl substituted -amino acids, their supramolecular assemblies, and their transmembrane channel properties. In this work, we are demonstrating the construction of chiral double helices with opposite handedness from the oligomers of alternating (E)-α,β-unsaturated 4, 4-dialkyl substituted -amino acids (E)-α,β-unsaturated 4-amino acids and the utilization of chiral double helices as transmembrane channels. Further, we investigated the conformational flexibility of the double helix to accommodate saturated -amino acids and the transformation of β-double helices into C14-helices by varying -amino acid content. Using fluorescent reporter groups, we demonstrated the formation of double helices from the linear peptides in solution. Additionally, these double helices are self-assembled into a remarkable porous framework through H-bond networks in the solid state. In continuation, we further designed double helices appended with electron-donating and electron-deficient systems and studied their conformations and their molecular assembly. Overall, we designed and studied new double helices from gamma-peptide foldamers. The new beta-double helices described here may serve as transmembrane channel-forming candidates, light harvesting, and conducting materials.