Stability and morphology comparisons of self-assembled virus-like particles from wild-type and mutant human hepatitis B virus capsid proteins.
Instead of displaying the wild-type selective export of virions containing mature genomes, human hepatitis B virus (HBV) mutant I97L, changing from an isoleucine to a leucine at amino acid 97 of HBV core antigen (HBcAg), lost the high stringency of selectivity in genome maturity during virion export. To understand the structural basis of this so-called "immature secretion" phenomenon, we compared the stability and morphology of self-assembled capsid particles from the wild-type and mutant I97L HBV, in either full-length (HBcAg1-183) or truncated core protein contexts (HBcAg1-149 and HBcAg1-140). Using negative staining and electron microscopy, full-length particles appear as "thick-walled" spherical particles with little interior space, whereas truncated particles appear as "thin-walled" spherical particles with a much larger inner space. We found no significant differences in capsid stability between wild-type and mutant I97L particles under denaturing pH and temperature in either full-length or truncated core protein contexts. In general, HBV capsid particles (HBcAg1-183, HBcAg1-149, and HBcAg1-140) are very robust but will dissociate at pH 2 or 14, at temperatures higher than 75 degrees C, or in 0.1% sodium dodecyl sulfate (SDS). An unexpected upshift banding pattern of the SDS-treated full-length particles during agarose gel electrophoresis is most likely caused by disulfide bonding of the last cysteine of HBcAg. HBV capsids are known to exist in natural infection as dimorphic T=3 or T=4 icosahedral particles. No difference in the ratio between T=3 (78%) and T=4 particles (20.3%) are found between wild-type HBV and mutant I97L in the context of HBcAg1-140. In addition, we found no difference in capsid stability between T=3 and T=4 particles successfully separated by using a novel agarose gel electrophoresis procedure.
Newman
Margaret
M
Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555-0609, USA.
Suk
Fat-Moon
FM
Cajimat
Maria
M
Chua
Pong Kian
PK
Shih
Chiaho
C
D002213:Capsid / Q000378:metabolism / Q000648:ultrastructure*; D036022:Capsid Proteins / Q000378:metabolism / Q000648:ultrastructure; D004587:Electrophoresis, Agar Gel; D006512:Hepatitis B Core Antigens / Q000378:metabolism / Q000648:ultrastructure; D006515:Hepatitis B virus / Q000378:metabolism / Q000648:ultrastructure*; D006801:Humans; D008854:Microscopy, Electron; D008958:Models, Molecular; D009154:Mutation; D016624:Negative Staining / Q000379:methods; D014771:Virion / Q000378:metabolism / Q000648:ultrastructure*; D019065:Virus Assembly
D036022:Capsid Proteins; D006512:Hepatitis B Core Antigens