An HBV large surface antigen protein which can be secreted from mammalian cells

The N-terminal 54 base pairs (encoding amino acid residues 2-19) within the preS1 region of the human hepatitis B virus surface antigen gene were deleted by site-directed mutagenesis. Unlike the wild type large surface antigen protein, when this mutated gene was expressed in monkey kidney cell line COS-M6, the protein product (S301 protein) could be secreted from the cells. Moreover, the inhibition of the secretion of the major surface antigen protein by this altered large surface antigen protein was greatly reduced, suggesting that the deleted region contained a retention sequence which prevented the secretion of the large surface antigen. However, the coexpression of the major S protein was essential for the secretion of the S301 protein. When coexpressed, the secretion of these two proteins was synchronous. Like the wild type large surface antigen protein, the S301 protein could be translocated into endoplasmic reticulum and glycosylated after its synthesis in COS cells. The S301 protein was thermostable and proteinase-resistant. It also retained the antigenicity of the large S and major S proteins. Given the fact that the S301 protein is readily secretable, stable and identical to the large S protein in terms of their antigenicity, it may be developed into a new generation of recombinant vaccine for the prevention of viral hepatitis.