All low density lipoprotein particles are partially desialylated in plasma

Desialylation has been proposed as a natural modification of low density lipoprotein (LDL) increasing atherogenicity. The galactose (Gal)-specific lectin, Ricinus communis agglutinin I (RCA120), has been used to analyse LDL prepared by different methods and it was found that more than 96% of LDL binds to the lectin. The bound LDL could be eluted with Gal or Lactose (Lac), but not with sialic acid, mannose (Man), glucose (Glu) or sodium chloride, indicating that binding occurs via exposed Gal residues on the LDL particle. When freshly isolated whole plasma was loaded on an RCA120 column, apo B-containing lipoproteins (including LDL) were quantitatively bound, whereas other glycosylated serum proteins, like transferrin, were not. Thus desialylation of LDL is not a consequence of its isolation from plasma, or a general property of all serum proteins. Analysis of apolipoprotein B from LDL indicates that only monodesialylated oligosaccharide chains are present, consistent with the rapid clearance of particles having biantennary Gal residues exposed.