Interactions of two neurosteroids, inhibiting membrane-bound N-Methyl-D-aspartate receptors, with
phospholipid membranes are studied. Namely, endogenous pregnanolone sulfate is compared with
pregnanolone glutamate, the latter being a novel synthetic steroidal inhibitor of these receptors with
potential pharmaceutical use. Molecular-level details of steroid-phospholipid membranes interactions
are scrutinized employing molecular dynamics simulations supported by quantum chemical calculations
to assess steroid lipophilicity. Moreover, permeability of both species across membranes is
experimentally evaluated by immobilized artificial membrane chromatography. We demonstrate that
while there is no significant difference of lipophilicity and membrane permeability between the two
steroids, they differ significantly regarding detailed localization in phospholipid membranes. The bulky
glutamate moiety of pregnanolone glutamate is
flexible and well exposed to the water phase while the
sulfate group of pregnanolone sulfate is hidden in the membrane headgroup region. This dissimilarity of
behavior in membranes can potentially account for the observed different activities of the two steroids
toward membrane-bound N-Methyl-D-aspartate receptors.