Retrovirus/HIV Flashcards
Retorvirus genes (4) and proteins
GAG- structural proteins (eg. capsid)
PRO- protease
POL- RT and integrase
ENV- glycoproteins for lipid bilayer envelop (gp120, gp41)
Features of retrovirus-
2 ssRNA strands with poly A tail
capsid with lipid bilayer envelop
Complex vs simple retrovirus
complex has more regulatory and accessory genes for mRNA
LTR?
Long terminal replete sequencces
flank ends of retroviral genome (TF binds here, regulatory sequencces)
Provirus?
retrovirus that integrates into host cell genome
Endogenous retrovirus?
integrates into germline DNA of ova and sperm (will be transmitted to offspring)
Two types of human retroviruses?
Oncoviruses and lentiviruses
Oncovirus mechanism and ex?
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
Lentivirus mechanism and ex
Nontransforming, just kills cell during viral replication
typically infects lymphocytes or NS
HIV
How HIV enters cell? What type of cell?
gp120 binds CD4 lymphocyte (also binds coreceptor: CCR5 or CXCR4)
gp41 (Transmembrane) fuses cell membrane with viral envelope
(Both are ENV proteins)
GAG gene proteins?
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)
PRO codes for?
Protease (cleaves GAG polypeptide)
POL codes for?
RT- RT has ribonuclease activity (digests RNA , leaving ssDNA)
Integrase- splices dsDNA of HIV into host DNA
5 types of anti-HIV drug targets
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)
Steps of HIV replication
- RT: RNA –> dsDNA (ribonuclease digests RNA)
- dsDNA circularizes (via matching LTR)
- integrase and dsDNA enter nucleus, insert
- with activation (nrmlly latent), TF binds LTR and starts synthesis
- structural prots and RNA produced; to cytoplasm, reassemble
- ENV proteins to cell membrane
- new capsid buds off with ENV glycoproteins
Preventing drug resistance to anitretrovirals?
Cocktail (3 drugs) to completely stop replication (no mutation)
HIV transmission rate between +/-? Factors that influence?
1/1000 per vaginal penile sex act (best case scenario)
- viral load
- disease stage (acute and end stage AIDS)
- circumcision
- STI coinfection
Specific mechanism of HIV entry
gp120 binds CD4 –> confo change, allows gp120 bind CCR5/CXCR4 –> confo change, expose gp41 (has hydrophobic tail that inserts to membrane) –> fusion
2 major HIV types
depends on the coreceptor it binds
- CCR5 mainly on macrophages (“MAC tropic”)
- CXCR4 “lymphotroic”
-“dualtropic” uses both
Which type of HIV is more common for sex transmitted HIV?
CCR5 “macrophage trophic”
Gene mutation protective against HIV infection?
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
Acute HIV infection
Seen in ~50% new infections
onset 2-6 weeks
fever, fatigue, sore throat, rash, diarrhea, large lymph nodes (similar to severe mono)
CD4+ cell count v clinical presentation
500+ is asymptomatic
Below 500 is symptomatic
Below 200 = AIDS
Below 50: 2year life expectancy
seroconversion to HIV?
Body detects HIV, makes antibody
Seropositive for HIV antibodies (diagnosis for HIV)
Seronegative window?
High levels of virus, but body has not made antibodies
CD8 role in immune response to HIV?
- 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)
HIV/AIDS diagnosis?
- 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)
