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MIMM 324 > 24. Picornaviruses & Togaviruses > Flashcards

24. Picornaviruses & Togaviruses Flashcards

1
Q

most well-known picornavirus?

A

poliovirus

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2
Q

how is polio transmitted?

A

fecal-oral

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3
Q

10 symptoms of polio

A
  1. fever
  2. headache
  3. vomiting
  4. diarrhea
  5. neck stiffness
  6. arm and leg pain
  7. muscle weakness
  8. paralytic poliomyelitis
  9. respiratory arrest
  10. death
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4
Q

what type of vaccine is the injected polio vaccine?

A

inactivated poliovirus vaccine (IPV)

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5
Q

how was the injected poliovaccine developed?

A

developed in monkey kidney cells and inactivated with formalin

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6
Q

what type of vaccine is the oral polio vaccine?

A

attenuated vaccine

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7
Q

how is the oral polio vaccine produced?

A

many passages in culture –> loses virulence via sequence change but still causes immune response

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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

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9
Q

what baltimore class are picornaviruses?

A

4 –> +RNA

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10
Q

Where does the name picornavirus come from?

A

PICO = small
RNA = RNA virus

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11
Q

are picornaviruses enveloped or naked?

A

naked

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12
Q

shape of picornavirus capsid? size?

A

icosahedral –> 25-30nm diameter

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13
Q

describe the picornavirus genome

A

monopartite, linear, 7-8.5kb

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14
Q

what type of picornavirus is poliovirus?

A

enteroviruses

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15
Q

3 examples of picornaviruses

A
  1. foot and mouth disease virus (animal stock)
  2. Hep A virus
  3. Rhinovirus
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16
Q

describe the 5’ UTR of picornavirus genome

A

cloverleaf + IRES + no cap

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17
Q

describe the 3’ UTR of picornavirus genome

A

polyA tail

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18
Q

describe the IRES of picornavirus genome

A

6 stem loops that bind viral proteins and host factors to initiate replication and translation

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19
Q

describe the production of proteins in picornavirus

A

1 long ORF that makes polyprotein that is cleaved to make individual proteins

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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

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21
Q

what are the 4 picornavirus capsid proteins?

A

VP1, VP2, VP3, VP4

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22
Q

describe the 3 P2 non-structural proteins in picornavirus and their functions

A
  1. 2A –> protease, host protein synthesis shutoff
  2. 2B –> cell permeability
  3. 2C –> vesicle formation
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23
Q

describe the 4 P3 non-structural proteins in picornavirus and their functions

A
  1. 3A –> cellular transport
  2. 3B –> VpG
  3. 3C –> protease, host transcription shutoff
  4. 3D –> RdRP
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24
Q

which picornavirus protease is responsible for most of the cleavage?

A

3C protein

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25
Q

how many copies of each capsid protein are there in each capsid of picornavirus?

A

60

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26
Q

describe the picornavirus life cycle (4 steps)

A
  1. some endocytosed, some inject their genome
  2. polyprotein is made in cytoplasm
  3. polyprotein is cleaved
  4. assembly
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27
Q

what are most picornavirus cellular receptors made of?

A

Ig-like

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28
Q

what are 3 types of receptors that rhinoviruses use to enter cells?

A
  1. ICAM
  2. LDLR
  3. CDHR3
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29
Q

which 2 picornaviruses use receptor-mediated endocytosis?

A
  1. rhinovirus
  2. FMDV
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30
Q

which picornavirus inject their viral RNA across the PM?

A

poliovirus

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31
Q

how do picornaviruses inject their RNA?

A

conformation change of VP1 where it inserts into membrane and makes channel with lipids that are inside cleft of VP1

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32
Q

how can the cleft of VP1 be used for drugs? downside?

A

drugs can bind in the cleft and prevent insertion but virus can mutate VP1 very rapidly and prevent drug binding

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33
Q

is picornavirus translation cap-dependent or cap-independent?

A

CAP-INDEPENDENT –> no 5’ cap

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34
Q

what is the cap-independent mechanism called?

A

Internal Ribosomal Entry Site (IRES) mechanism

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35
Q

what does IRES allow?

A

allows viral translation during host protein synthesis shutoff

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36
Q

describe the IRES mechanism in comparison to cap-dependent mechanism

A

3C protease cleaves eIF4G so only part of it can bind IRES with host factors –> shuts off host translation and allows viral translation

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37
Q

what is the dilemma of +RNA viruses?

A

cannot translate and make -RNA at the same time

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38
Q

describe the switch from translation to replication

A
  1. 3C protease cleaves host PCBP2
  2. PCBP2 loses interaction with translation complex
  3. then allows for -RNA synthesis for replication
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39
Q

does poliovirus use a nt primer for RNA synthesis?

A

NO

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40
Q

what is the primer for poliovirus RNA synthesis? how does it work?

A

VpG primer –> has OH on conserved tyrosine to make 1st linkage

41
Q

describe poliovirus RNA replication

A

UU-VpG primer binds polyA tail of +RNA and RNA pol adds nt to make -RNA

42
Q

where does picornavirus replication occur?

A

on virus-induced cellular vesicles

43
Q

how are vesicles induced for picornavirus replication?

A

induced by viral proteins 2B, 2C, 2A

44
Q

what is the role of virus-induced cellular vesicles?

A

REQUIRED for picornavirus RNA replication –> acting as nucleation site for replication complex formation

45
Q

describe the 2 types of virus-induced vesicles for picornavirus

A
  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
Q

what is the role of PCbp?

A

anchors proteins at viral replication complex to allow elongation for replication

47
Q

describe the 5 steps for virion assembly

A
  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
Q

Which 3 cellular processes are inhibited by picornaviruses?

A
  1. protein synthesis
  2. transcription
  3. cellular secretion
49
Q

in vitro system for production of infectious poliovirus (4 steps)

A
  1. put poliovirus DNA in plasmid
  2. in vitro +RNA synthesis
  3. transfect into cultured cells
  4. virus is produced
50
Q

where does the name togavirus come from?

A

latin for gown or cloak

51
Q

2 genera of togaviridae

A
  1. Rubivirus
  2. Alphavirus
52
Q

is togavirus enveloped or naked?

53
Q

what is unique about togavirus envelope?

A

has lipid envelope proteins that assemble into icosahedral envelope

54
Q

shape and size of togavirus capsid?

A

icosahedral and 70nm diameter

55
Q

what baltimore class is togavirus?

A

4 –> +RNA

56
Q

4 qualities of togavirus genome

A
  1. +RNA
  2. monopartite
  3. linear
  4. 9-11kb
57
Q

disease associated with rubivirus

A

Rubella Virus

58
Q

Rubella aka

A

Rubella aka german measles or 3-day measles

59
Q

symptoms of rubella virus

A

fever and rash (mild)

60
Q

how is rubella spread?

A

thru air via coughing

61
Q

how is rubella transmitted?

A

HUMANS only

62
Q

how effective is rubella vaccine?

63
Q

what are Arboviruses?

A

Arthropod-Borne Viruses –> transmitted by arthropod vectors

64
Q

what type of hosts do arboviruses replicate in?

A
  1. cold-blooded arthropods
  2. warm-blooded vertebrate hosts

VERY ADAPTABLE!

65
Q

is arbovirus infection in insects cytopathic?

A

no but it is persistent

66
Q

3 families of arboviruses

A
  1. Togaviridae
  2. Flaviviridae
  3. Bunyaviridae
67
Q

what type of togaviridae are arboviruses?

A

alphaviruses

68
Q

transmission cycle of alphaviruses

A

mosquitos are primary vector and can pass to other animals which pass it to humans as incidental hosts

69
Q

explain Chikungunya disease

A

“disease that bends up the joints”

70
Q

which 2 types of mosquitos transmit Chikungunya?

A
  1. Aedes aegypti
  2. Aedes albopictus
71
Q

what percent of Chikungunya cases are asymptomatic?

A

5-25% of cases

72
Q

7 symptoms of Chikungunya

A
  1. abrupt fever
  2. severe joint pain, arthritis
  3. skin rash
  4. myalgia
  5. neurological issues
  6. cardiac issues
  7. death
73
Q

what type of people does chikungunya cause death in?

A

babies, >65 years, and immunocompromised

74
Q

where in the world is Chikungunya disease most common? why?

A

in southern hemisphere because persists in mosquitos

75
Q

describe the togavirus genome organization

A

2 open reading frames: non-structural proteins and structural proteins

76
Q

what are the 4 nonstructural togavirus proteins and their roles?

A
  1. nsP1 –> RNA capping enzyme (methyltransferase)
  2. nsP2 –> protease/helicase
  3. nsP3 –> unknown function
  4. nsP4 –> RdRP
77
Q

what are the 4 structural proteins of togavirus and their roles?

A
  1. C –> capsid
  2. PE2 –> precursor to E2
  3. 6K –> assembly
  4. E1 –> envelope glycoprotein
78
Q

togavirus structure:

A
  1. envelope protein that spans the lipid bilayer membrane
  2. capsid protein
  3. viral RNA inside capsid
79
Q

how many copies are there of E1, E2, and capsid proteins?

A

240 copies

80
Q

togavirus life cycle (4 steps)

A
  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
Q

what is the major difference in togavirus and picornavirus life cycles?

A

togavirus RNA is transcribed in 2 diff regions

82
Q

what is the role of E2? what happens if there are mutations in E2 protein?

A

E2 can bind Laminin and Heparin sulfate receptors in culture

mutations in E2 can alter receptor binding

83
Q

in general, describe virus entry and uncoating of togavirus

A

entry = receptor-mediated endocytosis

uncoating = pH drop in endosomes causes conformational change in E1/E2 leading to membrane fusion and release of nucleocapsid

84
Q

describe genomic togavirus at 5’ and 3’ ends

A

5’ –> methylated cap
3’ –> polyA tail

85
Q

are nonstructural proteins of togavirus translated directly from genome or from replicated RNA?

A

nonstructural proteins are translated directly from genome

86
Q

describe readthrough of togavirus nonstructural proteins translation

A

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
Q

P123 and P1234 are both ________

A

P123 and P1234 are both core of replication complex

88
Q

describe P123 in replication

A

nsP4 (RdRP) partially/cis cleaved off of P1234 but still associated to P123–> allows -RNA synthesis

89
Q

what 2 things can the partially cleaved NSP catalyze?

A
  1. -RNA synthesis
  2. transcription of subgenomic mRNA
90
Q

what do subgenomic mRNA encode for?

A

structural proteins

91
Q

cis-cleaved NSP vs trans-cleaved NSP

A

cis-cleaved is partially cleaved and can catalyze -RNA

trans-cleaved is proteolytically cleaved and can catalyze +RNA and subgenomic mRNA production

92
Q

where does togavirus replication occur?

A

on cytopathic vacuoles

93
Q

describe cytopathic vacuole formation

A

dsRNA spherules form at the PM –> internalized by endo-lysosomal pathway to form cytopathic vacuoles

94
Q

what happens to the structural proteins of togavirus?

A

cleaved during translation and directed to diff cellular locations

95
Q

what happens to the capsid proteins of togavirus?

A

capsids self-cleave and bind packaging signal in genomic RNA to form nucleocapsids

96
Q

what happens to pE2, 6K, and E1 in togavirus?

A

processed by host signal peptidase and furin protease in ER

97
Q

when does modification of envelope proteins occur for togavirus?

A

during translocation thru trans-golgi network as they move to cell surface

98
Q

how does togavirus exit the cell?

99
Q

how does togavirus budding occur?

A

capsid proteins interact with cytoplasmic tails of envelope proteins on cell surface –> virions exit the cell by budding

MIMM 324 (37 decks)

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