Lecture 12 Flashcards
Macromolecular Synthesis
permissive cell
allow for productive virus replication
resistant cell
does not express the virus receptor
movement of large protein complexes will not occur by diffusion because
the cytoplasm is crowded
membrane fusion is regulated by
viral fusogens, (enveloped glycoproteins)
fusion is highly _____
regulated
what are the appropriate conditions for fusion
- lower pH: plasma membrane (pH 7) or an endosomal membrane (pH 5-6)
- binding to a second protein co-receptor (on plasma membrane or endosomal)
- proteolytic cleavage (activates fusion protein)
fusion at the plasma membrane examples
sendai: viral attachment protein binds to receptor to stimulate a change and simulate a fusion peptide
HIV: viral attachment protein, interacts with receptor for HIV, binds to CCR and stimulates a change to push the fusion peptide in
fusion at an endosomal membrane
- virions enter by endocytosis
- acidification changes conformation of VAP (low pH)
- reveals a hydrophobic fusion peptide
- fusion peptide penetrates host membrane
- further conformational change fuses membranes
what viruses are already on the “right side” of the membrane
enveloped viruses
how does a non-enveloped virus cross a membrane
makes a hole
how does a non-enveloped virus make a hole through the membrane
conformational changes in the capsid expose something hydrophobic: hydrophobic amino acid sequence, fatty acid
conformational changes can be due to
binding receptors, proteolysis, pH changes, etc
what promotes membrane reorganization
hydrophobic domains from viral fusogen
what is membrane reorganization
pore formation, membrane dissolution, usually use receptor-mediated endocytosis leading to endosomes
poliovirus (non-enveloped) makes what size holes
small
adenovirus (enveloped) makes what size hole
large
poliovirus entry
-binds to its receptors
-conformational change reveals myristic acid
-myristic acid is ejected into membrane and disrupts the membrane
-allows hydrophobic amino acid residues to penetrate membrane
-creates a small pore in membrane
-the +ssRNA genome is injected directly into cytoplasm
adenovirus entry
-initial binding to CAR by adenovirus fiber
-secondary binding to integrin
-acidification in endosome degrades capsid
-protein VI penetrates endosomal membrane
-membrane disruption allows remaining capsid to associate with microtubules and traffic nucleus
viral polymerases
transcription and genome replication
RNA viruses
-replicate in cytoplasm
-virus must use a viral polymerase
-viral RdRP generates both mRNA and new viral genomes
- +RNA virus must make a RdRP before any other transcription
- -RNA must package a RdRP in the virions
DNA viruses
-replicate in the nucleus
-use Pol II to transcribe mRNA
-use host DNA-dependent DNA polymerases to replicate their genome
-drive cell cycle to S-phase
-replication is divided into early and late genome replication
leaky scanning
-viral mRNA have start codons, can have poor Kozak consensus sequence
-scanning small ribosome subunit can sometimes miss these AUGs
-eg. Paramyxoviridae (measles)
polyprotein synthesis
-entire viral genome is translated as a giant protein
-viral proteases self-cleave out and further process the genome
-eg. Picornaviridae (polio), Coronaviridae (SARS)
why are virus particles built from sub-assemblies
ensures orderly formation and concentration dependent formation of viral particles
how are virus particles built from sub-assemblies
formation of discrete intermediate structures
P1 cleaved to capsid proteins VP1, VP3, and VP0
these proteins assemble into pentamers which can form empty capsids
packaging of genome and cleavage of VP0 to VP2 and VP4 by a viral protease locks the capsid
virus assembly occurs in
concentrated viral factories that are often visible by like microscopy
viruses concentrate ______
proteins
assembly and egress
acquiring an envelope
virus can acquire a membrane from cellular membranes, often the plasma membrane
viral glycoproteins accumulate on plasma membrane
recruit other viral proteins and the viral genome (matrix and nucleocapsid)
virion buds from surface
virions can also acquire envelopes from
anywhere in the secretory system
some virions require ______
maturation
APUTTGAR(M)
maturation
proper maturation is required for virion infectivity in some viruses
e.g. HIV Gag polyprotein cleavage is prevented by protease inhibitors (Antivirals)
