Ca2+-induced self-assembly in designed peptides with optimally spaced gamma-carboxyglutamic acid residues

We have previously elucidated a new paradigm for the metal ion-induced helix-helix assembly in the natural gamma-carboxyglutamic acid (Gla)-containing class of conantokin (con) peptides typified by con-G and a variant of con-T con-T[K7Gla] independent of the hydrophobic effect In these metallo zipper structures Gla residues spaced at i i+4 i+7 i+11 intervals which is similar to the arrangement of a and d residues in typical heptads of coiled-coils coordinate with Ca2+ and form specific antiparallel helical dimers In order to evaluate the common role of Gla residues in peptide self-assembly we extend herein the same Gla arrangement to designed peptides NH2-(gamma LS gamma EAK)(3)-CONH2 (peptide 1) and NH2-gamma LS gamma EAK gamma LS gamma QAN gamma LS gamma KAE-CONH2 (peptide 2) Peptide 1 and peptide 2 exhibit no helicity alone but undergo structural transitions to helical conformations in the presence of a variety of divalent canons Sedimentation equilibrium ultracentrifugation analyses showed that peptide 1 and peptide 2 form helical dimers in the presence of Ca2+ but not Mg2+ Folding and thiol-disulfide rearrangement assays with Cys-containing peptide variants indicated that the helical dimers are mixtures of antiparallel and parallel dimers which is different from the strict antiparallel strand orientations of con-G and con T[K7 gamma Gla] dimers These findings suggest that the Gla arrangement i i+4 i+7 i+11 i+14 plays a key role in helix formation without a strict adherence to strand orientation of the helical dimer (C) 2010 Elsevier Inc All rights reserved