Computational chemical study about the difference of behaviors of γ-PGAs depend on their secondary structures

Abstract

γ Poly glutamic acid (γ-PGA) has attracted great attention in various areas such as cosmetics because of its high water holding ability. Since the γ-PGA has one stereogenic center, there are L-γ PGA, D-γ-PGA and the mixed L,D-γ-PGA. It is believed that the secondary structure of L-γ-PGA is helical and that of the mixed D,L-γ-PGA is non-helical, although the structural detail of helix has not been disclosed. In this study, we investigate the helical structures of L-γ PGA and D,L-γ-PGA in detail. To this end, several helix models were constructed and compared. As a result, the helix which has 5 residues/helical cycle is the most stable in L-γ-PGA helices. It has been suggested experimentally that the viscosity of L-γ-PGA is higher than that of D,L-γ-PGA; that is, the distribution of L-γ-PGAs might be uniform in aqueous solution, and that of D,L-γ-PGA might not. We confirmed the difference in the distribution by using Monte Carlo (MC) simulation. We programmed our original MC simulation, and the interaction energy functions used in the MC simulation are simply Lennard-Jones' 6-12 potential and dipole-dipole interaction.