Title : Glycosylation and
sialylation of macrophage-derived human
apolipoprotein E analyzed by
SDS-PAGE and mass spectrometry: evidence for a novel
site of glycosylation on
Ser290
Abstract :
- Apolipoprotein E ( apoE ) is a 34-kDa glycoprotein secreted from various cells including hepatocytes and macrophages and plays an important role in remnant lipoprotein clearance, immune responses, Alzheimer disease, and atherosclerosis
- Cellular apoE and plasma apoE exist as multiple glycosylated and sialylated glycoforms with plasma apoE being less glycosylated/sialylated than cell-derived apoE
- Some of the glycan structures on plasma apoE are characterized; however, the more complicated structures on plasma and cellular/secreted apoE remain unidentified
- We investigated glycosylation and sialylation of cellular and secreted apoE from primary human macrophages by one- and two-dimensional gel electrophoresis and mass spectrometry
- Our results identify eight different glycoforms with (HexNAc)(2)-Hex(2)-(NeuAc)(2) being the most complex glycan detected on Thr(194) in both cellular and secreted apoE
- Four additional glycans were identified on apoE ( 283-299 ), and using beta-elimination/alkylation by methylamine in vitro, we identified Ser(290) as a novel site of glycan attachment
- Comparison of plasma and cellular/secreted apoE from the same donor confirmed that cell-derived apoE is more extensively sialylated than plasma apoE
- Given the importance of the C terminus of apoE in regulating apoE solubility, stability, and lipid binding, these results may have important implications for our understanding of apoE biochemistry