Orientation of lutein in a lipid bilayer - revisited.

Lutein is present in the human retina and lens, where it plays a protective role. As lutein is associated with the lipid matrix of biomembranes, the role depends on its membrane location. Experimental studies predicted two orientations of lutein in a phosphatidylcholine (PC) bilayer: vertical and horizontal. Using a molecular dynamics simulation, we observed, in two different PC bilayers, both orientations of lutein, and in each bilayer, a single change from vertical to horizontal orientation or vice versa. Both orientations were stabilized by hydrogen bonding of lutein OH groups with mainly carbonyl but also phosphate oxygen atoms of PC.