The structure of polyunsaturated lipid bilayers important for rhodopsin function: a neutron diffraction study

Abstract

The structure of oriented 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine bilayers with perdeuterated stearoyl- or docosahexaenoyl hydrocarbon chains was investigated by neutron diffraction. Experiments were conducted at two different relative humidities, 66 and 86%. At both humidities we observed that the polyunsaturated docosahexaenoyl chain has a preference to reside near the lipid water interface. That leaves voids in the bilayer center that are occupied by saturated stearoyl chain segments. This uneven distribution of saturated- and polyunsaturated chain densities is likely to result in membrane elastic stress that modulates function of integral receptor proteins like rhodopsin.

FIGURE 1

Diffraction data of 18:0-22:6-PC oriented multilayers, with protonated hydrocarbon chains (black), with deuterated stearoyl chains (orange), or with deuterated DHA chains (blue).

FIGURE 2

Scattering length density distributions of lipid hydrocarbon chains and water calculated as density difference of bilayers with protonated and deuterated hydrocarbon chains. The line width reflects the uncertainty bands. The SLDs reflect higher densities of DHA (blue) near the lipid water interface and of SA (red) in the bilayer center as shown in the model above the graph.