Structure of the cholesteryl ester core of human plasma low density lipoproteins: selective deuteration and neutron...

The structural arrangement of cholesteryl esters in human plasma low density lipoproteins (LDL) has been studied by selective deuteration and neutron small-angle scattering. LDL were labeled by in vitro exchange with two different kinds of deuterated cholesteryl esters, one labeled in the fatty acyl chain (cholesteryl myristate-d27) and the other in the branched side chain of cholesterol (cholesteryl-25,26,27-d7 oleate). Neutron scattering data from deuterated and protonated LDL were compared to identify the locations of the fatty acyl and cholesterol side chain moieties. Below the thermotropic transition, radii of gyration of 60 A and 70 A were obtained for these two domains, respectively, indicating that the cholesteryl nuclei are situated more distantly from the center than the fatty acyl chains. At 37 degrees C, above the thermotropic transition of the cholesteryl esters in LDL, both parts have similar radii of gyration of approximately 56 A. This information is used in a discussion of possible structural models for the apolar lipid core of LDL.