Can ionic effects induce α-sheet conformation of Peptides?

Highlights: • DFT data in aqueous solvent finds that α-sheet form of Ac-Ala₄-NMe is comparable in energy to β-strand. • Multiple cation-oxygen contacts in α-sheet stabilise this form further, especially for K⁺. • Two "real" peptides taken from PDB differ in response to ions. We report coupled cluster, MP2 and DFT data on the relative energy and geometry of α-sheet and β-strand conformations of model peptides. We show that ionic effects have a strong effect on energy balance through formation of multiple cation-oxygen contacts in the α-sheet form. Such effects are markedly dependent on both sequence and ion: two peptides considered favour α-sheet in the presence of cations, whereas a third, non-polar one favours β-strand in the same conditions.