how do enveloped viruses penetrate the membrane
fusion at plasma membrane
fusion in endosome
how do naked viruses enter the membrane
puncture
injection
endocytic lysis
whats the pH at fusion at the plasma membrane
neutral
how is fusion at the plasma membrane initiated
protein cleavage
receptor binding
how is fusion in the endosome triggered
low pH
3 triggering events for fusion
receptor binding
protein cleavage
endosome acidification
what does a fusion trigger do
induces a major change in protein structure of virions fusion proteins - releases a hydrophobic fusogenic domain (fusion peptide)
what draws viral and cellular membranes together to initiate fusion
protein hairpin formation
what is the pH when fusion is activated by receptor binding
neutral because there’s no change in pH on the outside of the cell
when there is a neutral pH, what is fusion triggered by
receptor binding or cleavage
what is not needed for syncytia formation
change in pH is not needed
how is fusion in an endosome activated
by the acidic pH of the endosome
class 1 fusion proteins
always trimers in endosome
influenza
class 2 fusion proteins
dimers that convert to homo-trimers in the endosome
semilike firest virus
dengue virus
what releases the fusion peptide in HA (influenza)
cleavage is required to activate it, a triggering event releases it
why must virus fusion be regulated
prevent premature fusion
maintain resistivity (fusion protein can only be triggered out once)
how do attachment proteins induce fusion (3)
pH change
cleavage
receptor binding
attachement protein
the viral surface protein whose main job is to bind to a receptor on the host cell
perforation
non enveloped viruses entire capsid is transferred through the membrane
endosome lysis
naked virus particles induce breakage of the membrane of cytoplasmic organelles
adenovirus
membrane puncture
naked virus generates a pore in the membrane through which the virus genome is released
poliovirus
2 nuclear import strategies
entry at the nuclear pore
wait in cytosol for the nuclear membrane dissolution during the cell cycle
where does the uncoating system come from
its built into the virion
what is needed for virus assembly ? and how does assembly forsure happen?
viral protein high in concentration at late times of the infection
and cellular factors required for uncoating are inactivated later (conditions in cytoplasm must be different)
