Structural heterogeneity of apoB-containing serum lipoproteins visualized using cryo-electron microscopy

Cryo-electron microscopy was used to analyze the structure of lipoprotein p articles in density gradient subfractions of human very low density lipopro tein (VLDL), intermediate density lipoprotein (IDL), and low density lipopr otein (LDL), Lipoproteins from a normolipidemic subject with relatively lar ge and buoyant LDL (pattern A) and from a subject with a predominance of sm all dense LDL (pattern B) were compared. Projections of VLDL in vitreous ic e were heterogeneous in size, but all were circular with a relatively even distribution of contrast. Selected projections of LDL, on the other hand, w ere circular with a high density ring or rectangular with two high density bands. Both circular and rectangular LDL projections decreased in average s ize with increasing subfraction density, but were found in all of 10 densit y gradient subfractions, both in pattern A and in pattern B profiles, Prepa rations of total IDL contained particles with the structural features of VL DL as well as particles resembling LDL, IDL particles resembling LDL were o bserved in specific density gradient subfractions in the denser region of t he VLDL-IDL density range, Within the group of IDL particles resembling LDL considerable heterogeneity was observed, but no structural features specif ic for the pattern A or pattern B lipoprotein profile were recognized. jlr The observed structural heterogeneity of the apolipoprotein B-containing se rum lipoproteins may reflect differences in the composition of these partic les that may also influence their metabolic and pathologic properties.