Versatile peptide rafts for conjugate morphologies by self-assembling amphiphilic helical peptides

Amphiphilic helical peptides with opposite helicities and different hydrophobic helical block lengths were combined to prepare self-assemblies in water for constructing novel morphologies. (Sar)25-b-(L-Leu-Aib)6 and (Sar)25-b-(D-Leu-Aib)6 (sarcosine (Sar) chain, a hydrophobic helix of leucine (Leu) and α-aminoisobutyric acid (Aib)) have been reported to self-assemble into well-defined nanotubes, but a 1:1 mixture of these components self-assembles into vesicles. Their mixtures at molar ratios 8:2 and 2:8 have yielded round-bottom flask-shaped molecular assemblies, which are an AB-type conjugate morphology of a vesicle (A) and a nanotube (B). Here, we expand the conjugate morphologies to new AB-type, ABA-type, ABA′-type and A3B-type. The new AB-type conjugate morphology had a nano-test-tube shape. Two types of the nano-test-tube-shaped self-assemblies were prepared using different combinations of nanotubes and vesicles. One thin nanotube was sealed with vesicles at both open ends to generate the ABA-type conjugate morphology with a dumbbell shape. When the round-bottom flask-shaped self-assembly was combined with a small vesicle, the ABA′-type conjugate morphology was obtained. The combination of a three-neck nanotube with a vesicle produced the A3B-type morphology. These self-assemblies were thermodynamically stable owing to the phase separation in their fused membranes. Therefore, these self-assemblies are termed ‘peptide rafts’ as an analogy to ‘lipid rafts’.