The antigenic structure of HBsAg: study of the d/y subtype determinant by chemical modification and site directed mutagenesis.

Lysine residue 122 of the major protein of HBsAg/adw has been shown previously to be involved in the d subtype determinant. We demonstrate here that the corresponding residue of the HBsAg/ayw, arginine 122, does not play such a critical role the y site of this antigen subtype. Thus, conversion by site directed mutagenesis of arginine 122 to lysine 122 in HBsAg/ayw does not result in the loss of y activity nor gain of d activity. Moreover, chemical modification studies of both the adw and ayw antigens with the reagents o-methylisourea and cyclohexanedione, demonstrate that arginine 122 plays at most only a minor role in this subtype antigenic site.