Hepatitis B virus capsid particles are assembled from core-protein dimer precursors.
Our studies on the assembly of hepatitis B virus capsids or core particles in Xenopus oocytes have demonstrated that unassembled p21.5 core proteins ("free p21.5") provide a pool of low-molecular-mass precursors for core-particle assembly. Here we have characterized this material. Free p21.5 sedimented through gradients of 3-25% sucrose (wt/vol) as a single protein species of approximately 40 kDa, corresponding to a p21.5 dimer. On nonreducing SDS/polyacrylamide gels, free p21.5 migrated as disulfide-linked p21.5 dimeric species of 35 and 37 kDa. Truncated core proteins lacking most or all of the 36-amino acid protamine region at the p21.5 carboxyl terminus were also found to behave as disulfide-linked dimers with appropriately reduced molecular masses. Our experiments failed to reveal monomeric core proteins or stable intermediates between dimers and capsids along the assembly pathway. We conclude that hepatitis B virus core particles are most likely assembled by aggregating 90 (or possibly 180) disulfide-linked p21.5 dimers. We discuss similarities between the assembly of hepatitis B virus capsids and simple T = 3 plant virus and bacteriophage structures.
Zhou
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Hormone Research Institute, University of California, San Francisco 94143-0534.
Standring
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D000818:Animals; D002213:Capsid / Q000096:biosynthesis* / Q000302:isolation & purification; D002499:Centrifugation, Density Gradient; D003545:Cysteine / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006515:Hepatitis B virus / Q000378:metabolism*; D046911:Macromolecular Substances; D008970:Molecular Weight; D009865:Oocytes / Q000378:metabolism; D010957:Plasmids; D011498:Protein Precursors / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D013462:Sulfur Radioisotopes; D014758:Viral Core Proteins / Q000302:isolation & purification / Q000378:metabolism*; D014981:Xenopus
D046911:Macromolecular Substances; D011498:Protein Precursors; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013462:Sulfur Radioisotopes; D014758:Viral Core Proteins; D003545:Cysteine