[转移帖]PLoS Pathog, 2010：HBV入核假说

cao1976

原帖由bigben发表于 2010-6-9 02:05 ：

Title: Nucleoporin 153 arrests the nuclear import of hepatitis B virus capsids in the nuclear basket.
Author: Schmitz, A.; Schwarz, A.; Foss, M. (...)
Source: PLoS Pathog, 2010, 6(1): e1000741

http://www.plospathogens.org/art ... ournal.ppat.1000741;jsessionid=051F510D741753C4C5B2A4CE33BE0B26

Abstract:
  Virtually all DNA viruses including hepatitis B viruses (HBV) replicate their genome inside the nucleus. In non-dividing cells, the genome has to pass through  the nuclear pore complexes (NPCs) by the aid of nuclear transport receptors as e.g. importin beta (karyopherin). Most viruses release their genome in the cytoplasm or at the cytosolic face of the NPC, as the diameter of their capsids exceeds the size of the NPC. The DNA genome of HBV is derived from reverse transcription of an RNA pregenome. Genome maturation occurs in cytosolic capsids  and progeny capsids can deliver the genome into the nucleus causing nuclear genome amplification. The karyophilic capsids are small enough to pass the NPC, but nuclear entry of capsids with an immature genome is halted in the nuclear basket on the nuclear side of the NPC, and the genome remains encapsidated. In contrast, capsids with a mature genome enter the basket and consequently liberate the genome. Investigating the difference between immature and mature capsids, we  found that mature capsids had to disintegrate in order to leave the nuclear basket. The arrest of a karyophilic cargo at the nuclear pore is a rare phenomenon, which has been described for only very few cellular proteins participating in nuclear entry. We analyzed the interactions causing HBV capsid retention. By pull-down assays and partial siRNA depletion, we showed that HBV capsids directly interact with nucleoporin 153 (Nup153), an essential protein of  the nuclear basket which participates in nuclear transport via importin beta. The binding sites of importin beta and capsids were shown to overlap but capsid binding was 150-fold stronger. In cellulo experiments using digitonin-permeabilized cells confirmed the interference between capsid binding and nuclear import by importin beta. Collectively, our findings describe a unique nuclear import strategy not only for viruses but for all karyophilic cargos.

cao1976

bigben发表于 2010-6-9 02:16 ：

Title: Nuclear entry of hepatitis B virus capsids involves disintegration to protein dimers followed by nuclear reassociation to capsids.
Author: Rabe, B.; Delaleau, M.; Bischof, A. (...)
Source: PLoS Pathog, 2009, 5(8): e1000563

http://www.plospathogens.org/art ... ournal.ppat.1000563

Abstract:
  Assembly and disassembly of viral capsids are essential steps in the viral life cycle. Studies on their kinetics are mostly performed in vitro, allowing application of biochemical, biophysical and visualizing techniques. In vivo kinetics are poorly understood and the transferability of the in vitro models to  the cellular environment remains speculative. We analyzed capsid disassembly of the hepatitis B virus in digitonin-permeabilized cells which support nuclear capsid entry and subsequent genome release. Using gradient centrifugation, size exclusion chromatography and immune fluorescence microscopy of digitonin-permeabilized cells, we showed that capsids open and close reversibly.  In the absence of RNA, capsid re-assembly slows down; the capsids remain disintegrated and enter the nucleus as protein dimers or irregular polymers. Upon the presence of cellular RNA, capsids re-assemble in the nucleus. We conclude that reversible genome release from hepatitis B virus capsids is a unique strategy different from that of other viruses, which employs irreversible capsid  destruction for genome release. The results allowed us to propose a model of HBV  genome release in which the unique environment of the nuclear pore favors HBV capsid disassembly reaction, while both cytoplasm and nucleus favor capsid assembly.

cao1976

jane200988发表于 2010-12-10 09:08 ：学习了，下次journal club讲这篇文章