A simulation on the complexation of cyclodextrins with phospholipid headgroups

The inclusion complexes of alpha-, beta- and gamma-cyclodextrin (CD) with three isolated phospholipid (PI - phosphatidylinositol; PS - phosphatidylserine; and PE - phosphatidylethanolamine) headgroups were studied using a flexible docking algorithm FDOCK based on molecular mechanics (CFF91 force filed). In the three phospholipid headgroups, PI headgroup exhibits the strongest affinity for CD, and the affinity of PS headgroup is greater than that of PE headgroup. By investigating the energy distribution and the complex structure in the inclusion procedure, it can be found that the van der Waals force is the main driving force responsible for the complexation. For the alpha-CD complex of PI headgroup, more than one inclusion complex should coexist due to the steric hindrance, which is reasonably consistent with the experimental results. Furthermore, analyses of the complex of PS and PE headgroup with alpha-CD also show that two or three possible complexes may appear in the inclusion process, and the complex structure with full inclusion is of the lowest energy and should be the most stable structure in the mixture. For beta- and gamma-CD, the energies of the most stable complexes structures for the three phospholipids headgroups were also discussed.