Figure 2.

Annular lipids. (a) Part of the transmembrane surface of aquaporin, showing bound annular lipid molecules. The protein is shown as a surface plot colored by charge (blue, positive; red, negative), with the lipid molecules shown in space-filling format (red, oxygen; orange, phosphorus; grey, carbon). From Protein DataBank (PDB) code 2B6O. (b) A snapshot from a molecular dynamics simulation of a transmembrane α-helix in a lipid bilayer. The helix is the sixth transmembrane α-helix of the potassium channel Kv. The lysine side chain can be seen hydrogen bonding to phosphate and ester oxygens of a phosphatidylcholine (PC) molecule, and the tryptophan side chain forms a hydrogen bond to an ester oxygen. Modified from [8].