Study of the glycosylation of apolipoprotein H

Apolipoprotein H is a single chain polypeptide composed of 326 amino acids highly glycosylated. Its carbohydrate content is approximately 19% of the m olecular weight. We show that it is rich in sialic acid linked alpha(2-6) t o galactose or N-acetylgalactosamine. Sialic acid is not alpha(2-3) linked to galactose. Galactose is beta(1-4) linked to N-acetylglucosamine and beta (1-3) linked to N-acetylgalactosamine. Carbohydrate O-linked chains (mainly sialic acid) are alpha(2-6) linked to galactose or N-acetylgalactosamine. Galactose is also organised in O-linked chains and beta(1-4) linked to N-ac etylglucosamine and beta(1-3) linked to acetylgalactosamine. Concanavalin A lectin was used to isolate two groups of apolipoprotein H molecules bearin g biantennary and truncated hybrids and high mannose and hybrid oligosaccha rides. Apolipoprotein H fails to bind lysine-Sepharose. Our results thus sh ow that it presents truncated hybrid or hybrid-type carbohydrate chains whi ch bear few unmasked mannose residues as a terminal sugar. Biochemical anal ysis of carbohydrate structures conducted on single isoforms separated thro ugh IEF revealed that no specific carbohydrate complex is bound to a single isoform. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.