Metal ion and proton stabilisation of turn motif in the synthetic octapeptide histidyltris(glycylhistidyl) glycine

Protonation and metal ion co-ordination can induce alpha- and gamma-turns respectively, of the linear octapeptide His-(Gly-His)(3)-Gly (His = histidine, Gly = glycine) and in both cases the imidazole groups of appropriately positioned His residues have been shown to be essential in the stabilisation of the folded structure; divalent metal ions exhibit different folding inducing ability of the octapeptide with Ni2+ having the greatest ability at physiological pH.