Molecular dynamics simulation of the hydrated phospholipid membrane built up by the unsaturated dioleylphosphatidylcholine (DOPC) molecules, containing a GM1 ganglioside molecule in each of its two layers has been performed. The system can be regarded as a model of the infinitely dilute solution of gangliosides in a phospholipid membrane, and can serve as a reference system for future studies of mixed membranes of finite concentration.
It is found that the GM1 ganglioside molecule, the headgroup of which is bearing a negative charge can form charge pairs with the positively charged choline group of the zwitterionic head of the DOPC molecules. This charge pair can involve either 1 or 2 nearest neighbour DOPC molecules. The observed lifetime of such a charge pair is in the order of a few nanoseconds, whereas the lifetime of a bifurcated charge pairing formed with two DOPC molecules is considerably shorter, being in the order of a few hundred picoseconds. The dipole vector of the polar headgroup of the DOPC molecules charge paired to GM1, represented by the vector pointing from their P to N atom (PN vector) prefers to point straight to the centre of the negative charge located at the C atom of the negatively charged carboxylic (COO -) group of the GM1 molecule.