A coarse-grained MARTINI model of polyethylene glycol and of polyoxyethylene alkyl ether surfactants

Nonionic surfactants are used for the isolation and purification of membrane proteins, as well as for the study of fundamental aspects of protein diffusion in membranes. Here we present a new coarse-grained model of polyethylene glycol (PEG) and of the family of polyoxyethylene alkyl ether (C(i)E(j)) surfactants. The model is compatible with the MARTINI coarse-grained force-field for lipids and proteins. We validate the model by comparing molecular dynamics simulations with experimental data. In particular, we show that the model reproduces the phase behavior of water-surfactant mixtures as a function of water concentration. We also simulate the self-assembly of two ternary mixtures that have been used for the experimental measure of protein diffusion coefficients. The first includes a cosurfactant that affects the curvature of the surfactant bilayers; the second is a mixture of C(i)E(j) surfactants, alkanes and water. In both cases, the results of self-assembly simulations are in agreement with experimental observations and pave the way to the use of the surfactant model in combination with MARTINI peptides and proteins.