A microscopic view of a helical poly(γ-peptide): Molecular dynamics simulations of a 20-residue un-ionized poly(γ-<SC>D</SC>-glutamic acid) in water

We present a molecular dynamics study of the helical conformation of the naturally occurring poly(γ-<SC>D</SC>-glutamic acid) in the un-ionized state. The study was conducted in both aqueous solution and gas-phase considering a 20 residue polypeptide. The results indicated that the left-handed helix with 19-membered ring hydrogen bonds set between the CO of the amide group i and the NH of amide group i + 3 is very stable in aqueous solution. This conformation was recently proposed for this poly(γ-amino acid) from a conformational search study. A detailed picture of the most relevant structural details of the helical conformation of poly(γ-<SC>D</SC>-glutamic acid) is provided.