LHDAg Hdv Rnp

Fig. 3 The S-HBsAg and L-HBsAg HBV envelope proteins are key elements of the HDV replication cycle. S-HBsAg and L-HBsAg are integral membrane proteins. S-HBsAg comprises TMD1 (I) between amino acid residues 4 and 24; the cytosolic loop (c.L.) 29-79; TMD2 (II) 80-100; the antigenic loop (a.l.) 101-164; two predicted carboxyl terminal TMDs, 173-193 and 202-222. L-HBsAg is identical to S-HBsAg except for the additional pre-S (pS) domain (pre-S1 + pre-S2) at its amino terminus. The pre-S1 domain contains a putative receptor binding site (thick line). For HDV morphogenesis, S-HBsAg proteins interact with each other and with L-HBsAg (step 1) to form aggregates that bud in the lumen of the IC. The HDV RNP is probably recruited by the envelope proteins through an interaction between S-HBsAg and L-HDAg (step 2). Viral entry is mediated by the L-HBsAg protein through an interaction between the pre-S1 domain and a receptor on the hepatocyte membrane (step 3). The glycosylation site (N146) in the antigenic loop is indicated. The broken line indicates the myristate group linked to the amino terminus of L-HBsAg. Elements important for interaction with L-HDAg are indicated: W196, W199, W201

was proven that the S-HBsAg protein could fulfill these functions on its own (Sureau et al. 1992; Wang et al. 1991). Hence, all the information necessary for assembly and secretion of HDV resides in the S-HBsAg polypeptide (Fig. 3).

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