Partial amino acid sequence of two major component polypeptides of hepatitis B surface antigen.

Abstract

Determination of the amino acid sequence of the immunogenic polypeptides of hepatitis B surface antigen may not only permit molecular localization of the distinct determinants a, d and y but may also lead to the synthesis of a hapten useful in prophylactic immunization against hepatitis B virus infection. For this purpose purified monotypic hepatitis B surface antigen of adw subtype was resolved into equal amounts of 2 major polypeptides (22,000 and 28,000 daltons) and up to 6 other minor polypeptides by polyacrylamide gel electrophoresis. With the periodate staining reaction only the 28,000-dalton polypeptide stained as a glycoprotein. Guinea pigs immunized with the 22,000-dalton polypeptide produced potent antisera against determinants a and d, but the 28,000-dalton glycoprotein did not induce a response. Both polypeptides isolated by preparative polyacrylamide gel electrophoresis showed amino acid composition identical with that of the intact antigen. For both polypeptides hydrazinolysis gave Ile as the carboxyterminus, and carboxypeptidase A digestion gave the same terminal sequence, Val-Tyr-Ile. Both peptides also yielded an identical sequence of amino acids in 9 steps of Edman degradation-Met-Glu-Asn-Ile-Thr-Ser(Cys)-Gly-Phe-Leu. Hepatitis B surface antigen probably contains a single major immunogenic 22,000-dalton polypeptide component, part of which is modified by the addition of carbohydrate to give rise to the glycopeptide of apparent MW 28,000.