| Abstract;Coiled coils, which mediate associations and regulate functions of various proteins, have a representative amino acid sequence of (defgabc)n and usually have hydrophobic residues at the a and d positions. We have designed a triple stranded parallel .ALPHA.-helical coiled coil, in which the amino acid sequence is YGG(IEKKIEA)4. To construct a peptide which undergoes a metal ion induced self-assembly, we engineered the metal binding site in the hydrophobic core of the coiled coil. We replaced two Ile residues of the third heptad with His residues. The peptide had a random structure in an aqueous solution. In contrast, in the presence of a transition metal ion, the peptide exhibited the .ALPHA.-helical conformation. The metal-complexed peptide was triple stranded and had a parallel orientation. We found that the dissociation constant is (4.3.+-.0.5)*10-14M3 for Co(II), (8.5.+-.1.7)*10-18M3 for Ni(II), (5.3.+-.0.8)*10-15M3 for Cu(II), and (1.2.+-.0.2)*10-14M3 for Zn(II). It was suggested that all of six His residues might ligate the metal ions with octahedral geometry. These results suggest that the peptide is a useful tool to control associations of functional domains attached to the peptide. (author abst.) |
