Nanometer to Millimeter-scale Peptide-Porphyrin Materials

摘要

AQ-Pal14 is a 30-residue polypeptide that was designed to form an α-helical coiled coil which contains a metal-binding 4-pyridylalanine residue on its solvent-exposed surface. However, characterization of this peptide shows that it exists as a three-stranded coiled coil, and not a two-stranded one as predicted from its design. Reaction with cobalt(III) protoporphyrin IX (Co-PPIX) produces a six-coordinate Co-PPIX(AQ-Pal14)2 species which creates two coiled-coil oligomerization domains coordinated to opposite faces of the porphyrin ring. It is found that this species undergoes a buffer-dependent self-assembly process: nanometer-scale globular materials were formed when these components were reacted in unbuffered H2O, while millimeter-scale rod-like materials were prepared when the reaction was performed in phosphate buffer (20 mM, pH 7). It is suggested that assembly of the globular material is dictated by the conformational properties of the coiled-coil forming AQ-Pal14 peptide, whereas that of the rod-like material involves interactions between Co-PPIX and phosphate ion.