Retrovirus/HIV

Question 0

Retorvirus genes (4) and proteins

Answer 0

GAG- structural proteins (eg. capsid)
PRO- protease
POL- RT and integrase
ENV- glycoproteins for lipid bilayer envelop (gp120, gp41)

Question 1

Features of retrovirus-

Answer 1

2 ssRNA strands with poly A tail

capsid with lipid bilayer envelop

Question 2

Complex vs simple retrovirus

Answer 2

complex has more regulatory and accessory genes for mRNA

Question 3

LTR?

Answer 3

Long terminal replete sequencces

flank ends of retroviral genome (TF binds here, regulatory sequencces)

Question 4

Provirus?

Answer 4

retrovirus that integrates into host cell genome

Question 5

Endogenous retrovirus?

Answer 5

integrates into germline DNA of ova and sperm (will be transmitted to offspring)

Question 6

Two types of human retroviruses?

Answer 6

Oncoviruses and lentiviruses

Question 7

Oncovirus mechanism and ex?

Answer 7

Transforming retrovirus
do not kill cell, make them immortal
ONC gene turns cell to oncogene
HTLV- human T cell lymphotrophic virus (has TAT gene that regulates viral replication) –> T cell leukemia

Question 8

Lentivirus mechanism and ex

Answer 8

Nontransforming, just kills cell during viral replication
typically infects lymphocytes or NS
HIV

Question 9

How HIV enters cell? What type of cell?

Answer 9

gp120 binds CD4 lymphocyte (also binds coreceptor: CCR5 or CXCR4)
gp41 (Transmembrane) fuses cell membrane with viral envelope

(Both are ENV proteins)

Question 10

GAG gene proteins?

Answer 10

4 cleaved from a polyprotein by protease (structural proteins)

• p24 forms capsid
• matrix protein on inner surface of lipid bilayer
• p7 and p9 (nucleic acid binding proteins)

Question 11

PRO codes for?

Answer 11

Protease (cleaves GAG polypeptide)

Question 12

POL codes for?

Answer 12

RT- RT has ribonuclease activity (digests RNA , leaving ssDNA)
Integrase- splices dsDNA of HIV into host DNA

Question 13

5 types of anti-HIV drug targets

Answer 13

RT antiretrovirals- nucleoside analogues to stop action (ex. AZT) or non-nucleoside inhibitors directly block RT activity
Protease inhibitors
Integrase inhibitors

Attachment/binding inhibitors (blocks gp120-CCR5)
Membrane fusion blocker (interferes with gp41)

Question 14

Steps of HIV replication

Answer 14

1. RT: RNA –> dsDNA (ribonuclease digests RNA)
2. dsDNA circularizes (via matching LTR)
3. integrase and dsDNA enter nucleus, insert
4. with activation (nrmlly latent), TF binds LTR and starts synthesis
5. structural prots and RNA produced; to cytoplasm, reassemble
6. ENV proteins to cell membrane
7. new capsid buds off with ENV glycoproteins

Question 15

Preventing drug resistance to anitretrovirals?

Answer 15

Cocktail (3 drugs) to completely stop replication (no mutation)

Question 16

HIV transmission rate between +/-? Factors that influence?

Answer 16

1/1000 per vaginal penile sex act (best case scenario)

• viral load
• disease stage (acute and end stage AIDS)
• circumcision
• STI coinfection

Question 17

Specific mechanism of HIV entry

Answer 17

gp120 binds CD4 –> confo change, allows gp120 bind CCR5/CXCR4 –> confo change, expose gp41 (has hydrophobic tail that inserts to membrane) –> fusion

Question 18

2 major HIV types

Answer 18

depends on the coreceptor it binds

• CCR5 mainly on macrophages (“MAC tropic”)
• CXCR4 “lymphotroic”

-“dualtropic” uses both

Question 19

Which type of HIV is more common for sex transmitted HIV?

Answer 19

CCR5 “macrophage trophic”

Question 20

Gene mutation protective against HIV infection?

Answer 20

CCR5 delta 32 bp deletion (homozygous)
–> short CCR5 protein (no extracell portion), resistant to HIV
(15% Europeans are carriers)

heterozygous has slow progression of disease

Question 21

Acute HIV infection

Answer 21

Seen in ~50% new infections
onset 2-6 weeks
fever, fatigue, sore throat, rash, diarrhea, large lymph nodes (similar to severe mono)

Question 22

CD4+ cell count v clinical presentation

Answer 22

500+ is asymptomatic
Below 500 is symptomatic
Below 200 = AIDS
Below 50: 2year life expectancy

Question 23

seroconversion to HIV?

Answer 23

Body detects HIV, makes antibody

Seropositive for HIV antibodies (diagnosis for HIV)

Question 24

Seronegative window?

Answer 24

High levels of virus, but body has not made antibodies

Question 25

CD8 role in immune response to HIV?

Answer 25

• Initial response is massive; direct killing (targets capsid)
• Contributes to “viral set point” (broader antigen recognition –> lower set point)
• secretes cytokine that block CCR5 binding
• BUT CD8+ function dependent on CD4+ cells (activated CD4+ preferentially infected; quickly eliminated by HIV)

Question 26

HIV/AIDS diagnosis?

Answer 26

• EIA (enzyme immunoassays)- test for HIV antibodies; highly sensitive
• Western blot- run viral proteins on gel, then add patient serum (aB will bind), then add labelled anti-IgG antibody (will show up as dark band)