  The MARTINI coarse-grained (CG) force field is used to test the ability of CG
models to simulate ionic transport through protein nanopores. The ionic
conductivity of CG ions in solution was computed and compared with experimental
results. Next, we studied the electrostatic behavior of a solvated CG lipid
bilayer in salt solution under an external electric field. We showed this
approach correctly describes the experimental conditions under a potential
bias. Finally, we performed CG molecular dynamics simulations of the ionic
transport through a protein nanopore ($\alpha$-hemolysin) inserted in a lipid
bilayer, under different electric fields, for 2-3 microseconds. The resulting
$I-V$ curve is qualitatively consistent with experiments, although the computed
current is one order of magnitude smaller. Current saturation was observed for
potential biases over $\pm~350$~mV. We also discuss the time to reach a
stationary regime and the role of the protein flexibility in our CG
simulations.
