A mechanism for the stabilization of the secondary structure of a peptide by liquid ethylene glycol and its aqueous solutions

Molecular dynamics (MD) simulations have been performed to investigate the effects of ethylene glycol (EG) on the stabilization of the secondary structure of a polyserine helical peptide. Three model systems containing one peptide chain with initial helical structure and the following solvent components were considered: (a) 1379 SPC water molecules; (b) 1606 EG molecules; (c) EG/water mixture containing 1307 EG and 1978 water molecules performing a 40:60 composition. MD simulations show peptide stabilization in liquid EG and in an EG/water mixture but denaturation in aqueous solution. In the EG/water mixture water molecules on the first peptide solvation shell were displaced by EG ones. Structural analyses demonstrate that EG molecules are capable of forming multiple hydrogen bonds with the peptide side-chains, thus preventing the rupture of the intrapeptide hydrogen bonds. Therefore, the peptide stabilization is explained by the intercalation of EG molecules between its side-chains. This mechanism can also explain the stability of proteins secondary structure in solutions containing EG molecules as cosolvents.