Sugar chain structure of apolipoprotein B-100 and its role in oxidation

The aim of this research was to determine the structure of oligosaccharide antennae located on the surface of apoB-100, and to examine their roles in the oxidation process and in the signal transduction of endothelial cells. The profiles of oligosaccharides on apoB-100 were determined by enzymatic digestions as follows. First, N-glycanase was used to release a mixture of oligomannose and complex types of oligosaccharides. Second, endoglycosidase H was used to release high-mannose and hybrid types. Third, O-glycosidase DS was used to release O-linked oligosaccharides. The released oligosaccharides were then labeled and quantified by electrophoresis. In vitro apoB-100 oxidation was mimicked by adding transition copper ions. For the signal transduction study, I examined the expression of adhesion molecules on cultured human coronary artery endothelial cells by adding LDL in which the oligosaccharide sequences were enzymatically modified. The sugar chain structures on the surface part of apoB-100 were composed predominantly of N-linked oligosaccharides, i.e., two forms of complex type and five forms of high-mannose type. The digestion of sugar chains by exoglycosidases and endoglycosidases did not result in any changes in the susceptibility of LDL to oxidation. Also, LDL without monosaccharides such as sialic acid, galactose, and N-acetylglucosamine did not induce any significant effect on the expression of ICAM-1, VCAM-1, or ELAM-1. I found that the sugar chains did not play any significant roles in the oxidative processing of LDL and also in the expression of ICAM-1, VCAM-1, or ELAM-1.