24. Picornaviruses & Togaviruses Flashcards
1
Q
most well-known picornavirus?
A
poliovirus
2
Q
how is polio transmitted?
A
fecal-oral
3
Q
10 symptoms of polio
A
- fever
- headache
- vomiting
- diarrhea
- neck stiffness
- arm and leg pain
- muscle weakness
- paralytic poliomyelitis
- respiratory arrest
- death
4
Q
what type of vaccine is the injected polio vaccine?
A
inactivated poliovirus vaccine (IPV)
5
Q
how was the injected poliovaccine developed?
A
developed in monkey kidney cells and inactivated with formalin
6
Q
what type of vaccine is the oral polio vaccine?
A
attenuated vaccine
7
Q
how is the oral polio vaccine produced?
A
many passages in culture –> loses virulence via sequence change but still causes immune response
8
Q
describe how incidence of polio changed in USA with oral and injected vaccines
A
oral vaccine decreased the incidence but virus mutated to cause cases in kids and immunocompromised ppl
9
Q
what baltimore class are picornaviruses?
A
4 –> +RNA
10
Q
Where does the name picornavirus come from?
A
PICO = small
RNA = RNA virus
11
Q
are picornaviruses enveloped or naked?
A
naked
12
Q
shape of picornavirus capsid? size?
A
icosahedral –> 25-30nm diameter
13
Q
describe the picornavirus genome
A
monopartite, linear, 7-8.5kb
14
Q
what type of picornavirus is poliovirus?
A
enteroviruses
15
Q
3 examples of picornaviruses
A
- foot and mouth disease virus (animal stock)
- Hep A virus
- Rhinovirus
16
Q
describe the 5’ UTR of picornavirus genome
A
cloverleaf + IRES + no cap
17
Q
describe the 3’ UTR of picornavirus genome
A
polyA tail
18
Q
describe the IRES of picornavirus genome
A
6 stem loops that bind viral proteins and host factors to initiate replication and translation
19
Q
describe the production of proteins in picornavirus
A
1 long ORF that makes polyprotein that is cleaved to make individual proteins
20
Q
describe the cleavage of picornavirus proteins
A
polypeptide cleaved into:
P1 = capsid proteins
P2 and P3 = non-structural proteins
^these are further cleaved into individual proteins
21
Q
what are the 4 picornavirus capsid proteins?
A
VP1, VP2, VP3, VP4
22
Q
describe the 3 P2 non-structural proteins in picornavirus and their functions
A
- 2A –> protease, host protein synthesis shutoff
- 2B –> cell permeability
- 2C –> vesicle formation
23
Q
describe the 4 P3 non-structural proteins in picornavirus and their functions
A
- 3A –> cellular transport
- 3B –> VpG
- 3C –> protease, host transcription shutoff
- 3D –> RdRP
24
Q
which picornavirus protease is responsible for most of the cleavage?
A
3C protein
25
how many copies of each capsid protein are there in each capsid of picornavirus?
60
26
describe the picornavirus life cycle (4 steps)
1. some endocytosed, some inject their genome
2. polyprotein is made in cytoplasm
3. polyprotein is cleaved
4. assembly
27
what are most picornavirus cellular receptors made of?
Ig-like
28
what are 3 types of receptors that rhinoviruses use to enter cells?
1. ICAM
2. LDLR
3. CDHR3
29
which 2 picornaviruses use receptor-mediated endocytosis?
1. rhinovirus
2. FMDV
30
which picornavirus inject their viral RNA across the PM?
poliovirus
31
how do picornaviruses inject their RNA?
conformation change of VP1 where it inserts into membrane and makes channel with lipids that are inside cleft of VP1
32
how can the cleft of VP1 be used for drugs? downside?
drugs can bind in the cleft and prevent insertion but virus can mutate VP1 very rapidly and prevent drug binding
33
is picornavirus translation cap-dependent or cap-independent?
CAP-INDEPENDENT --> no 5' cap
34
what is the cap-independent mechanism called?
Internal Ribosomal Entry Site (IRES) mechanism
35
what does IRES allow?
allows viral translation during host protein synthesis shutoff
36
describe the IRES mechanism in comparison to cap-dependent mechanism
3C protease cleaves eIF4G so only part of it can bind IRES with host factors --> shuts off host translation and allows viral translation
37
what is the dilemma of +RNA viruses?
cannot translate and make -RNA at the same time
38
describe the switch from translation to replication
1. 3C protease cleaves host PCBP2
2. PCBP2 loses interaction with translation complex
3. then allows for -RNA synthesis for replication
39
does poliovirus use a nt primer for RNA synthesis?
NO
40
what is the primer for poliovirus RNA synthesis? how does it work?
VpG primer --> has OH on conserved tyrosine to make 1st linkage
41
describe poliovirus RNA replication
UU-VpG primer binds polyA tail of +RNA and RNA pol adds nt to make -RNA
42
where does picornavirus replication occur?
on virus-induced cellular vesicles
43
how are vesicles induced for picornavirus replication?
induced by viral proteins 2B, 2C, 2A
44
what is the role of virus-induced cellular vesicles?
REQUIRED for picornavirus RNA replication --> acting as nucleation site for replication complex formation
45
describe the 2 types of virus-induced vesicles for picornavirus
1. EARLY in infection --> single membrane vesicles holding dsRNA are derived from ER and golgi
2. LATER in infection --> vesicles wrap around themselves to form double membrane vesicles
46
what is the role of PCbp?
anchors proteins at viral replication complex to allow elongation for replication
47
describe the 5 steps for virion assembly
1. protomer of VP0, VP1, VP3
2. pentamer of 5x VP0, VP1, VP3
3. procapsid of 60x VP0, VP1, VP3
4. provirion with packaged RNA
5. virion of 60x VP1, VP2, VP3, VP4
48
Which 3 cellular processes are inhibited by picornaviruses?
1. protein synthesis
2. transcription
3. cellular secretion
49
in vitro system for production of infectious poliovirus (4 steps)
1. put poliovirus DNA in plasmid
2. in vitro +RNA synthesis
3. transfect into cultured cells
4. virus is produced
50
where does the name togavirus come from?
latin for gown or cloak
51
2 genera of togaviridae
1. Rubivirus
2. Alphavirus
52
is togavirus enveloped or naked?
enveloped
53
what is unique about togavirus envelope?
has lipid envelope proteins that assemble into icosahedral envelope
54
shape and size of togavirus capsid?
icosahedral and 70nm diameter
55
what baltimore class is togavirus?
4 --> +RNA
56
4 qualities of togavirus genome
1. +RNA
2. monopartite
3. linear
4. 9-11kb
57
disease associated with rubivirus
Rubella Virus
58
Rubella aka
Rubella aka german measles or 3-day measles
59
symptoms of rubella virus
fever and rash (mild)
60
how is rubella spread?
thru air via coughing
61
how is rubella transmitted?
HUMANS only
62
how effective is rubella vaccine?
95%
63
what are Arboviruses?
Arthropod-Borne Viruses --> transmitted by arthropod vectors
64
what type of hosts do arboviruses replicate in?
1. cold-blooded arthropods
2. warm-blooded vertebrate hosts
VERY ADAPTABLE!
65
is arbovirus infection in insects cytopathic?
no but it is persistent
66
3 families of arboviruses
1. Togaviridae
2. Flaviviridae
3. Bunyaviridae
67
what type of togaviridae are arboviruses?
alphaviruses
68
transmission cycle of alphaviruses
mosquitos are primary vector and can pass to other animals which pass it to humans as incidental hosts
69
explain Chikungunya disease
"disease that bends up the joints"
70
which 2 types of mosquitos transmit Chikungunya?
1. Aedes aegypti
2. Aedes albopictus
71
what percent of Chikungunya cases are asymptomatic?
5-25% of cases
72
7 symptoms of Chikungunya
1. abrupt fever
2. severe joint pain, arthritis
3. skin rash
4. myalgia
5. neurological issues
6. cardiac issues
7. death
73
what type of people does chikungunya cause death in?
babies, >65 years, and immunocompromised
74
where in the world is Chikungunya disease most common? why?
in southern hemisphere because persists in mosquitos
75
describe the togavirus genome organization
2 open reading frames: non-structural proteins and structural proteins
76
what are the 4 nonstructural togavirus proteins and their roles?
1. nsP1 --> RNA capping enzyme (methyltransferase)
2. nsP2 --> protease/helicase
3. nsP3 --> unknown function
4. nsP4 --> RdRP
77
what are the 4 structural proteins of togavirus and their roles?
1. C --> capsid
2. PE2 --> precursor to E2
3. 6K --> assembly
4. E1 --> envelope glycoprotein
78
togavirus structure:
1. envelope protein that spans the lipid bilayer membrane
2. capsid protein
3. viral RNA inside capsid
79
how many copies are there of E1, E2, and capsid proteins?
240 copies
80
togavirus life cycle (4 steps)
1. endocytosed and releases capsid and RNA
2. non-structural proteins made first
3. forms replication complex which makes negative strand intermediate
4. -RNA makes 2 transcripts: nonstructural proteins and structural proteins
81
what is the major difference in togavirus and picornavirus life cycles?
togavirus RNA is transcribed in 2 diff regions
82
what is the role of E2? what happens if there are mutations in E2 protein?
E2 can bind Laminin and Heparin sulfate receptors in culture
mutations in E2 can alter receptor binding
83
in general, describe virus entry and uncoating of togavirus
entry = receptor-mediated endocytosis
uncoating = pH drop in endosomes causes conformational change in E1/E2 leading to membrane fusion and release of nucleocapsid
84
describe genomic togavirus at 5' and 3' ends
5' --> methylated cap
3' --> polyA tail
85
are nonstructural proteins of togavirus translated directly from genome or from replicated RNA?
nonstructural proteins are translated directly from genome
86
describe readthrough of togavirus nonstructural proteins translation
10-20% of the time, there is a bad stop codon so it makes full-length P1234 polyprotein
if stop codon works, makes shorter P123 polyprotein
87
P123 and P1234 are both ________
P123 and P1234 are both core of replication complex
88
describe P123 in replication
nsP4 (RdRP) partially/cis cleaved off of P1234 but still associated to P123--> allows -RNA synthesis
89
what 2 things can the partially cleaved NSP catalyze?
1. -RNA synthesis
2. transcription of subgenomic mRNA
90
what do subgenomic mRNA encode for?
structural proteins
91
cis-cleaved NSP vs trans-cleaved NSP
cis-cleaved is partially cleaved and can catalyze -RNA
trans-cleaved is proteolytically cleaved and can catalyze +RNA and subgenomic mRNA production
92
where does togavirus replication occur?
on cytopathic vacuoles
93
describe cytopathic vacuole formation
dsRNA spherules form at the PM --> internalized by endo-lysosomal pathway to form cytopathic vacuoles
94
what happens to the structural proteins of togavirus?
cleaved during translation and directed to diff cellular locations
95
what happens to the capsid proteins of togavirus?
capsids self-cleave and bind packaging signal in genomic RNA to form nucleocapsids
96
what happens to pE2, 6K, and E1 in togavirus?
processed by host signal peptidase and furin protease in ER
97
when does modification of envelope proteins occur for togavirus?
during translocation thru trans-golgi network as they move to cell surface
98
how does togavirus exit the cell?
budding
99
how does togavirus budding occur?
capsid proteins interact with cytoplasmic tails of envelope proteins on cell surface --> virions exit the cell by budding
