Construction of Polypeptide Tertiary Structure by the Template-Assisted Synthesis

Abstract

Two helical chains of dodecapeptides were connected to a cyclic octapeptide in a parallel (F12-C8KL) or an antiparallel orientation (CH2). CD measurements revealed that two dodecapeptide chains took α-helical conformation and were non-aggregative in organic solvents, but assembled intramolecularly in a buffer solution. The formation of the supersecondary structure was also indicated by fluorescent probes introduced to the chain- end region. Since each peptide chain was designed to take an amphiphilic α-helical structure, the hydrophobic surfaces face each other in the α-helix assembly. The intramolecular assembly caused a distortion of peptide chains from α-helical conformation in a buffer solution. The distortion of CH2 was less marked than that of F12-C8KL. CH2 was bound by λ DNA, while CHI, which is a single-chain analog of CH2, and F12-C8KL, which is analoguous to CH2 without a terminal anthryl group, were not. It is considered that CH2 binds itself to DNA backbone through electrostatic interaction of two Lys residues in one chain, and that the anthryl group of the other chain is intercalated into a base pair. The mechanism of CH2/DNA interaction changed by the addition of Ca²⁺ probably due to Ca²⁺ complexation with the cyclic moiety of CH2.