FUNCTIONS OF THE LARGE HEPATITIS-B VIRUS SURFACE PROTEIN IN VIRAL PARTICLE MORPHOGENESIS

The hepatitis B virus (HBV) envelope and the subviral lipoprotein part icles contain three viral surface proteins (L, M, and S) which are exp ressed from one open reading frame by the usage of three start codons and a common stop codon. The largest surface protein L has some unusua l properties. It adopts two different transmembrane topologies due to a posttranslational switch of the folding in approximately half of the L proteins. L molecules which expose their N-terminal preS1 domain on the viral particle surface are probably ligands for a putative virus receptor and determine the species specificity and liver tropism of th is virus. L chains with internal preS1 domains are required in virion morphogenesis and mediate the contact to the nucleocapsid like a matri x protein. Overexpression of this form of the L protein is also respon sible for the inhibition of viral particle release. This short review summarizes our knowledge on the biosynthesis and maturation of the HBV surface proteins and their functions in viral particle morphogenesis with special emphasis on the L protein.