Self-assemblies of triskelion A2B-type amphiphilic polypeptide showing pH-responsive morphology transformation

A pH-responsive rolled-sheet morphology was prepared from a triskelion A(2)B-type amphiphilic polypeptide having a histidine residue as a pH-responsive unit. The dimensions of the rolled sheet were 85 nm diameter and 210 nm length with a sheet turn number of 2.0 at pH 7.4. Upon decreasing the pH from 7.4 to 5.0, the layer spacing of the rolled sheets was widened from ca. 9 to ca. 19 nm due to electrostatic repulsion caused by histidine protonation. This morphology change occurred reversibly with a pH change between 7.4 and 5.0. The molecular packing in the rolled sheets was shown to be loosened at pH 5.0 on the basis of electron diffraction measurements. The tightness of the rolled sheets was thus controlled reversibly by a pH change due to a single protonation in the amphiphilic polypeptide.

Morphology transformation via pH-triggered self-assembly of peptides

Three flexible peptides (P1: (C(17)H(35)CO-NH-GRGDG)(2)KG; P2: (Fmoc-GRGDG)(2)KG; P3: (CH(3)CO-NH-GRGDG)(2)KG) self-assembled to form a variety of morphologically distinct assemblies at different pHs. P1 formed nanofibers at pH 3, then self-assembled into nanospheres with pH up to 6 and further changed to lamellar structures when the pH value was further increased to 10. P2 aggregated into an entwined network structure at pH 3, and then self-assembled into well-defined nanospheres, lamellar structures, and vesicles via adjusting the pH value. However, P3 did not self-assemble into well-ordered nanostructures, presumably due to the absence of a large hydrophobic group. The varying self-assembly behaviors of the peptides at different pHs are attributed to molecular conformational changes. These self-assembled supramolecular materials might contribute to the development of new peptide-based biomaterials.

Temperature-triggered fusion of vesicles composed of right-handed and left-handed amphiphilic helical peptides

Vesicles prepared from a mixture of (Sar)(25)-b-(L-Leu-Aib)(6) (SLL) and (Sar)(25)-b-(D-Leu-Aib)(6) (SDL) fused with themselves upon heating to 90 °C. The vesicles also fused with (Sar)(28)-b-(L-Leu-Aib)(8) vesicles upon heating to 90 °C. The temperature-triggered fusion was due to the phase transition of the mixed membrane of SLL and SDL at 90 °C and should be driven by the bending energy stored in the stereocomplex membrane upon taking a vesicular structure.