Metal Ion Induced Folding of a de Novo Designed Coiled-Coil Peptide

Abstract

A disulfide-bridged two-stranded α-helical coiled-coil peptide has been designed which undergoes a random coil to α-helical transition at pH 7 and 20 °C upon metal binding to two sites engineered into the molecule. The metal binding coiled-coil, dubbed Gla2Nx, is composed of identical 35 residue polypeptide chains based on the “Native” heptad sequence repeat QgVaGbAcLdQeKf and contains a Cys substitution for Val at position 2 to allow formation of an interchain disulfide bridge. The coiled-coil structure is destabilized in the apo form by two interhelical i to i‘ + 5 ionic repulsions between negatively charged γ-carboxyglutamic acid (Gla) side chains at position 15 of one strand and position 20 of the other strand. In contrast, the folded form is stabilized by metal binding because the metal is chelated by the Gla side chains which otherwise (in the absence of metal) repel one another. One such metal binding interaction was predicted to occur between each pair of repelling Gla side chains. Metal titration...