A microscopic view of a helical poly(gamma-peptide): Molecular dynamics simulations of a 20-residue unionized poly(gamma-D-glutamic acid) in water

We present a molecular dynamics study of the helical conformation of the na turally occurring poly(gamma -D-glutamic acid) in the un-ionized state. The study was conducted in both aqueous solution and gas-phase considering a 2 0 residue polypeptide. The results indicated that the left-handed helix wit h 19-membered ring hydrogen bonds set between the CO of the amide group i a nd the NH of amide group i + 3 is very stable in aqueous solution. This con formation was recently proposed for this poly(gamma -amino acid) from a con formational search study. A detailed picture from a conformation of poly(ga mma -D-glutamic acid) is provided.