Journal of Lipid Research, Vol 38, 659-669, Copyright © 1997 by Lipid Research, Inc.

ARTICLES

Cryo-electron microscopy of low density lipoprotein and reconstituted discoidal high density lipoprotein: imaging of the apolipoprotein moiety

R van Antwerpen, GC Chen, CR Pullinger, JP Kane, M LaBelle, RM Krauss, C Luna- Chavez, TM Forte and JC Gilkey
Department of Biochemistry, University of Arizona, Tucson 85721, USA.

Cryo-electron microscopy was used to analyze the structure of low density lipoprotein from normolipidemic subjects (N-LDL), phospholipid- depleted N-LDL (PD-LDL), small dense LDL from hypertriglyceridemic subjects (SD-LDL), and reconstituted discoidal high density lipoproteins (rHDL). In different projections of N-LDL, a high density component of the particle was visible as two parallel bands or as a single ring. Projections of PD-LDL were very similar to those of N-LDL, indicating that the contribution of phospholipid headgroups to the observed high density structure is minor. In preparations of SD-LDL, projections with two high density bands or a single high density ring were rare. Instead, triangular and diamond-shaped projections were recognized. In different projections of discoidal rHDL, a high density component was visible as a single band or as a single ring. The present results indicate that cryo-electron microscopy reveals the distribution of apolipoproteins within lipoprotein particles. Thus, apolipoprotein B- 100 (apoB) in N-LDL appears to be organized as a double ring around the particle, while apoB in SD-LDL is indicated to have a different conformation. Cryo-electron micrographs of rHDL are consistent with the presence of apolipoprotein A-I on the periphery of the lipoprotein disc.
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