Carbohydrate Composition of Hepatitis B Surface Antigen

This 1977 study determined the carbohydrate composition of hepatitis B surface antigen (HBsAg) using gas chromatography. Researchers purified approximately 20 mg of highly purified HBsAg from plasma using multiple centrifugation and precipitation methods, then analyzed carbohydrate content after delipidation. The main carbohydrate components identified were N-acetylglucosamine (45.8 μg/mg protein), mannose (12.1 μg/mg protein), galactose (8.3 μg/mg protein), and sialic acid (8.5 μg/mg protein), with trace amounts of fucose. No N-acetylgalactosamine was detected. The total carbohydrate content was 75.8 μg/mg protein. Critically, no sugars were found in lipid-containing fractions, indicating that carbohydrates in HBsAg exist exclusively as glycoproteins rather than glycolipids, contradicting previous reports. The high N-acetylglucosamine content supports the hypothesis that carbohydrate chains are linked to the protein backbone via asparagine-N-acetylglucosamine linkages. The sugar composition suggests the presence of both acidic complex and mannose-based oligosaccharide chains in HBsAg.

Key findings

• HBsAg contains 75.8 μg carbohydrate per mg protein, primarily composed of N-acetylglucosamine, mannose, galactose, and sialic acid
• Carbohydrates in HBsAg exist exclusively as glycoproteins; no glycolipids were detected despite previous reports
• The high N-acetylglucosamine content and absence of N-acetylgalactosamine suggest protein-sugar linkage occurs via asparagine rather than serine or threonine residues
• Sugar composition indicates both acidic complex and simple mannose-based oligosaccharide chains are present in HBsAg