The oligosaccharide structure of human C4 was studied by using C4 purified from plasma and C4 secreted by human hepatoma-derived cell line, HepG2. The α- and β-chains of human C4 are glycosylated, whereas the γ-chain is devoid of carbohydrate. The α-chain has three complex fucosylated oligosaccharides of the biantennary type, one each on the α2, α3, and α4 fragments. The β-chain has a single high mannose oligosaccharide primarily of the Man9GlcNAc2 type. The ~2000 M(r) difference between the α-chains of the two C4 gene products (C4A and C4B) was localized to the α2 fragment and is not due to carbohydrate. Sulfation of the C4 α-chain was localized to the α4 fragment of the α-chain. Hence, the M(r) difference between the two gene products is likely to reside in amino acid differences. The oligosaccharide structure of three incompletely processed C4 molecules was also analyzed. These molecules have the oligosaccharide composition of the appropriate individual subunits. Therefore, intracellular proteolytic processing to the multi-chain form of C4 is not required for proper oligosaccharide processing.
|Number of pages||9|
|Journal||Journal of Immunology|
|State||Published - Jan 1 1985|