Journal of Lipid Research, Vol 35, 2223-2231, Copyright © 1994 by Lipid Research, Inc.
Cryo-electron microscopy reveals human low density lipoprotein substructure
R Van Antwerpen and JC Gilkey
Department of Biochemistry, University of Arizona, Tucson 85721.
In the present study, we have examined the structure of human low density
lipoprotein (LDL) using cryo-electron microscopy. Human LDL particles were
analyzed in a vitrified frozen-hydrated condition, without chemical
fixation or any form of staining. Hence, the lipoproteins were visualized
close to their native state. Contrary to current spherical models, the
overall shape of human LDL is indicated to be discoidal. The observed LDL
disks have a diameter of 21.4 +/- 1.3 nm and a height of 12.1 +/- 1.1 nm
(mean +/- standard deviation). The average volume of LDL particles in
cryo-electron microscopic preparations is estimated to be 4352 nm3. This
value corresponds well with the LDL volume that has been determined by
sedimentation equilibrium studies [4130-4803 nm3; Kahlon et al., 1982.
Lipids. 17: 323-330]. Details of LDL ultrastructure, visible as a result of
local differences in mass density, are indicated to reflect the
distribution of protein within the lipoprotein particle. Thus,
apolipoprotein B-100 (apoB) appears to form two ring-shaped structures that
are organized around the perimeter of the LDL disk.