16. Parvovirus Flashcards
2 general characteristics of parvovirus
- icosahedral
- 18-26nm diameter
3 characteristics of parvovirus genome
- ssDNA
- 4-6kb
- linear
2 general types of parvovirus
- autonomous
- requires helper virus
what is an autonomous virus?
infects cells that are already dividing
what does it mean for parvoviruses to require a helper virus?
requires adenovirus to be able to replicate
example of parvovirus requiring helper virus
dependovirus
what does densovirus infect?
insects, silkworms
what happens with canine parvovirus?
infects puppies and can cause death
what happens with feline panleukopenia?
infects cats and affects blood formation and cause death
why do parvoviruses often infect young animals?
because they are still growing so their cells are still dividing –> better for parvovirus
what parvovirus infects humans?
B19
what type of parvovirus is B19?
autonomous
what happens if a pregnant person is infected with B19 for the first time?
can cause severe anemia, Hydrops fetalis which can lead to miscarriage
what happens with B19 infection?
infects erythroid progenitors, leading to anemia and reduced blood cells in circulation
what disease in children can B19 cause? what symptom does it cause? how is it treated?
Erythema Infectiosum aka Fifth Disease
causes rash on cheeks
just wait for it to be resolved
how was B19 discovered?
in sera of patient with severe anemia
why does B19 infect erythroid precursor?
they still have their nuclei and are rapidly proliferating
what are the main capsid proteins in parvovirus? and their relative amounts
VP1: 60 copies, 3 per face
less VP2 and VP3
do parvovirus capsid proteins self-assemble?
yes, they self-assemble into VLP
do the positive or negative regions of parvovirus interact with receptors?
positive
why does AAV have spiky proteins on the outside?
to reduce antibody efficacy in animals
why does densovirus not have spiky proteins on the outside?
because densovirus infects insects but insects don’t have antibodies
describe general parvovirus genome structure
- 2 promoters
- encodes non-structural/replicase protein and viral/cap protein
- each end has different structures
describe general dependovirus genome structure
- 3 promoters
- encodes non-structural/replicase protein and viral/cap protein
- each end has identical structures
describe general B19 genome structure
- 1 promoter
- encodes non-structural/replicase protein, viral/cap protein, and extra protein
- each end has identical structures
describe general densovirus structure
- 2 promoters in opposite direction
- encodes non-structural/replicase protein and viral/cap protein
- each end has identical structures
what is the purpose of the dsDNA structures on the ends of ssDNA? how do they form?
form via complementary repeats for replication and packaging
do all parvoviruses use the same receptor for entry?
no
what receptor is used by B19 for entry?
erythrocyte P antigen –> surface protein on erythrocytes and pre-erythrocytes
what receptor is used by CPV/FPV for entry?
transferin receptor –> found on most cells for iron transport
what receptor is used by AAV for entry?
heparin sulphate or EGFR integrins –> diff receptors by diff AAV
how does parvovirus enter the cell?
endocytosis
how is the virus released from the endosome?
endosome acidifies, which changes conformation of capsid and releases phospholipase so it can leave endosome
how does the virus enter the nucleus?
via a nuclear localization signal from the virus
function of inverted terminal repeats on the ends of DNA?
DNA polymerase can use them as primer for dsDNA
does parvovirus use primers?
no, it is self-priming
describe the 5 steps of DNA replication:
- DNA pol extends 3’ end from inverted terminal repeat
- NS1/rep protein binds original strand and nicks with endonuclease activity
- NS1/rep protein unwinds the hairpin and the 3’ OH at the nick site can be extended by DNA pol
- hairpin refolds and DNA pol continues extending 3’ end
- 1 ssDNA and 1 dsDNA product are produced
what is the name for parvovirus replication?
Rolling Hairpin Replication
describe the promoter and coding/non-coding regions of MVM genome and how this corresponds to early/late genes
p4 promoter for early genes (NS1/2) in coding region at beginning of transcript (end of transcript is non-coding in early phase)
then, p38 promoter for late genes (VP1/VP2) in coding region at end of transcript
describe the promoter and coding/non-coding regions of AAV genome and how this corresponds to early/late genes
p5 and p19 make diff truncated versions of replicase in coding region at beginning of transcript (end of transcript is non-coding in early phase)
p40 promoter for late genes (VP1/2/3) in coding region at end of transcript
parvovirus genomes has binding sites for ______ ________
parvovirus genomes has binding sites for transcription factors
what is an important transcription factor that binds MVM and other autonomous parvovirus genome?
E2F
why is it important that autonomous parvovirus genomes bind E2F?
Allows the virus to sense that Rb is phosphorylated so the cell is actively replicating and making S phase genes
what binds both the early and late transcripts for autonomous parvovirus?
why?
NS1 –> binds at promoter region to increase transcription
how does adenovirus help AAV?
E1A protein turns on early and late promoter
besides E1A, what protein binds AAV transcript? early or late?
NS1/rep78 binds early transcript to make NS1
what allows for AAV early transcription?
E1A induced S phase activation
what happens if a dependovirus infects a cell that is not actively replicating / no adenovirus is present? (3 steps)
- ssDNA is turned into dsDNA
- Rep78 allows dsDNA to integrate into host chromosome
- virus sits latent
what happens if an adenovirus infects a cell with latent parvovirus? (3 steps)
- adenovirus mediates S phase
- Rep78 allows parvovirus genome to be released
- parvovirus co-replicates with adenovirus
besides replication, how are the dsDNA structures used?
recognized by capsid proteins for assembly
if the genome has inverted repeats on the ends, is the (+) or (-) sense strand added?
either, bc both ends have the same structure
if the genome has unique structures on each end, is the (+) or (-) sense strand added?
it depends, but a specific virus will only use one or the other
4 functions of NS1/Rep78
- binding viral DNA to induce late gene expression
- ATPase dependent helicase to unwind viral DNA
- sequence specific endonuclease to begin replication
- keeps cells in S phase
what type of therapy is AAV used for?
AAV is used as a vector for gene therapy
5 advantages of gene therapy vector
- does not cause disease in humans
- different AAV serotypes use diff receptors so can target specific tissue
- low toxicity
- stable expression (observed up to 1 year)
- can genetically manipulate bc small genome
3 steps of producing AAV as gene therapy vector
- remove rep and cap from genome and add transgene with strong promoter
- transfect in E1-expressing cell with AAV helper and AD helper
- produces recombinant virus particles that cannot replicate and only deliver genes of interest
what is the AAV helper?
contains rep and cap
what is the AD helper?
contains E2A, E4, VARNA
why do you need AAV and AD helpers?
bc the virus with transgene is dead so must have genes that can allow virus particles to be made
AAV vectors have different _____ to target different areas
AAV vectors have different capsids to target different areas of body
7 diseases that AAV can be used for:
- PKU
- Hemophilia A
- Hemophilia B
- Duchenne’s Muscular Dystrophy
- Aromatic amino acid decarboxylase (AADC) deficiency
- mutation associated retinal dystrophy
- spinal muscular atrophy
how much does 1 dose of Zolgensma cost for spinal muscular atrophy?
$2.8 million
