Cryo-electron microscopy of low density lipoprotein and reconstituted discoidal high density lipoprotein: imaging of the apolipoprotein moiety.
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.
van Antwerpen
R
R
Department of Biochemistry, University of Arizona, Tucson 85721, USA.
Chen
G C
GC
Pullinger
C R
CR
Kane
J P
JP
LaBelle
M
M
Krauss
R M
RM
Luna-Chavez
C
C
Forte
T M
TM
Gilkey
J C
JC
D016632:Apolipoprotein A-I / Q000737:chemistry; D015925:Cryopreservation; D006801:Humans; D007053:Ice; D008075:Lipoproteins, HDL / Q000737:chemistry / Q000648:ultrastructure*; D008077:Lipoproteins, LDL / Q000737:chemistry / Q000648:ultrastructure*; D008854:Microscopy, Electron / Q000379:methods*
D016632:Apolipoprotein A-I; D007053:Ice; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL