A) Overall structure of human PC-TP. The α-helix identifiers and residue ranges for human PC-TP are α1 (9–22), α2 (64–74), α3 (75–82) and α4 (184–209). The β-strand identifiers and residue ranges are β1 (31–36), β2 (39–46), β3 (51–61), β4 (84–93), β5 (96–104), β6 (111–123), β7 (130–138), β8 (150–162) and β9 (168–178). The Ω-loop identifiers and residue ranges are Ω1 (105–110) and Ω2 (139–149). B) Interactions of PC-TP (blue) with the glycerol-3-phosphorylcholine moiety of 1-palmitoyl,2-linoleoyl-sn-glycerol-3-phosphorylcholine (palmitoyl-linoleoyl phosphatidylcholine) (yellow). The structure of 1,2-dilinoleoyl-sn-glycerol-3-phosphorylcholine (dilinoleoyl phosphatidylcholine) from the PC-TP–phosphatidylcholine complex is superimposed (gray). C) Solvent accessible volume of the binding pocket containing phosphatidylcholine. The phosphatidylcholine molecule occupies approximately 89% of the lipid binding pocket, which extends through two narrow portals 3–5 Å in diameter to bulk solvent. (Reprinted with permission from reference [26]).

The C-terminus of PC-TP is the membrane binding domain. A) The α4 helix of the C-terminus of PC-TP can be subdivided into two functionally distinct types, a membrane spanning helix (α4a) and an amphipathic helix (α4b). B) A model of PC-TP-membrane binding that occurs when α4b aligns at the surface of a bilayer. Extraction of a phosphatidylcholine may be accomplished when α4a penetrates into the membrane.