Hepatitis B surface antigen assembles in a post-ER, pre-Golgi compartment

The consensus view of HBsAg assembly localized the processes which convert the monomeric, transmembrane HBsAg protein to the oligomeric, soluble lipoprotein particle to the ER. Here, we present evidence that the later stages of this process, in which the I-IBsAg lipoprotein particle is assembled from dimeric HBsAg, occurs in an intermediate compartment between the ER and the Golgi. This result expands our understanding of the assembly pathway of this lipoprotein particle and of the role of this intermediate compartment in biosynthesis in that assembly utilizes the special environment in this compartment to promote the extensive disulphide crosslinking of the HBsAg particle. Once again, a study of the way in which a virus exploits the cellular machinery has resulted in a better understanding of that machinery.