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The Structure of Polyunsaturated Lipid Bilayers Important for Rhodopsin Function: A Neutron Diffraction Study

Mihaela Mihailescu ^* and Klaus Gawrisch 

^* Department of Physiology and Biophysics, University of California, Irvine, California; and Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland 20892

Correspondence: Address reprint requests and inquiries to Klaus Gawrisch, E-mail: gawrisch{at}helix.nih.gov.

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.