Lec 4 - assembly, exit and exocytosis Flashcards
how do viruses ensure the proteins find each other to assemble in cellular environemnt
proteins are made in massive excess
where are sites of assembly of viruses in a cell
internal membranes
provides a means of concentrating protein
where does polio virus assemble
- disassembles the Golgi apparatus
- produces tubules and vesicles for it to use
what things does host provide for viral assembly
- host cell machinery (some)
- chaperones
- cellular transport systems (MT)
- host secretory pathway
- host nuclear import and export machinery
4 types of AA sequences viral proteins have to ensure correct localisation
- signal seq
- retention seq
- nuclear localisation seq
- nuclear export seq
example of assembly from individual protein molecules
- simian virus 40
- only 2 types of proteins made
- one central and 5 units to form the entamer
- correct stoichiometry needed when proteins being made
exmaple of assembly from polyprotein protein
- poliovirus
- all 4 proteins it needs to form a unit are translated as ONE protein
- otherwise impossible to find each other
- when its folded, the links get cleaved
- and forms a unit
(no issues with stoichiometry)
how is bacteriophage T4 formed
- assembly ine, ordely fasion
- allows assembly of the more complex viruses
- discreet intermediate structures made
- wont proceed unless previous structure formed
- head, tail, tail fibres
- then assembled
examples of self assembled viruses
- TMV
- Polio
- Haemagglutinin of influenza
- hep B (surface antigen can form virus like particles)
what are scaffolding proteins
- needed for assisted assembly of more complex proteins
- TRANSIENT intermediate structures
how are scaffolding porteins transient
- not in the mature virus
- proteolytic degradation by viral proteases prior to DNA genome entry into capsid
herpes simplex 1
- linear ds DNA
- memb bound, icosohedral
- targets mucosal epithelial cells
herpes simplex virus 1:
inital scaffolding protein subunit name
> pre-VP22a
stimulates binding of VP5 structural protein
and Vp23 and VP19C triplexes
VP5, VP23 and VP19C are part of mature virus
how is scaffold in herpes simplex 1 dismantles
VP24 protease
- cleaves c terminal sequences from the scaffolding protein
- degrades scaffolding proteins
- conformational change = VP5 hexamers and pentamers tightly associate AND dna genome can enter via UL6 portal
what are the scaffolding proteins used for adenovirus
L1 52/55