Lec 6 - Virus assembly, maturation and release Flashcards
What are the steps in a general assembly?
- Synthesise structural units
- Assemble capsid
- Package genome into capsid
- Acquire envelope if needed
- Release from cell
- Mature if needed
List the sites of assembly in a eukaryotic cell
Cell membrane, nuclear membrane, nucleus, ER, cytoplasm
How do viral proteins enter the nucleus?
Importins transport viral proteins from dyneins through nuclear pore complex with nuclear localisation sequence
Briefly describe the 3 types of assembly
- From folded protein monomers
- From polyproteins: viral protease cleaves them to monomers
- Assisted assembly: chaperones move subunits to correct position and fold unnecessary proteins
Describe the protein subunits, chaperone, and other proteins in polyomavirus assembly
VP1 and VP3 capsid proteins need chaperone Hsc70 with ATPase activity that’s activated by viral large T antigen
What are scaffold proteins?
Support forming capsids but are not incorporated into mature virion
Compare concerted and sequential assembly
Concerted: capsid and genome assemble together
Sequential: procapsid then genome assemble
How are envelopes obtained?
Capsid interacts with membrane bound by spike proteins then virion pinches off
Describe the assembly of HIV
- CA capsid proteins assemble in a ring of MA matrix proteins
- Genome associates with NC proteins inside capsid
- Structural polyproteins gag and gag-pol cleaved and incorporated
How does HIV mature and what shape is associated with maturity?
Mature HIV is cone shaped from viral protease cleaving gag and gag-pol polyproteins
What are the functions of HIV’s Nef and Vpu accessory proteins?
Nef: downregulate MHC-1, packages CD4 in vesicles
Vpu: translocates vesicles with CD4 to proteosome for degradation
How does adenovirus cause cell lysis?
Viral transmembrane death protein accumulates, allowing virions to burst out
