Position and orientation of gallated proanthocyanidins in lipid bilayer membranes: influence of polymerization degree and linkage type.

It is well known that the biological activity of gallated proanthocyanidins (PAs) is highly structure-dependent. Polymerization degree (DP) and linkage types affect their biological activity greatly. Positions and orientations of gallated PAs in lipid bilayer reveal their structure-function activity at the molecular level. The present work aimed at determining the locations and orientations of epigallocatechin-3-gallate (EGCG) and its derivatives: A-type and B-type EGCG dimers and trimers in 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) and 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE) lipid bilayer via molecular dynamic (MD) simulations. The results showed that EGCG and its derivatives localized in the lipid bilayer or on the bilayer/water interface. Their penetration depths and orientations depended on both DP and linkage types. The penetration depths decreased with the increase of DP, sequencing to be EGCG > EGCG dimers > EGCG trimers. Spatially stretched A-type PAs could form more hydrogen bonds (H-bonds) with deep oxygen atoms of lipid bilayer and have higher affinity to the lipid bilayer than B-type PAs. Our results will provide an explicit evidence for PAs' distinct biological activities.