HIV Virology/Replication Flashcards
(34 cards)
HIV is surrounded by a lipid membrane with two different membrane associated proteins. What are these two proteins?
- gp41: transmembrane glycoprotein
- gp120: A docking protein.
take the 1’s away from these proteins and you get 420 remember?
HIV has 3 enzymes that it uses to take over. What are they?
- Protease
- Integrase
- Reverse transcriptase
What kind of virus is HIV? DNA? RNA?
RNA retrovirus. It goes from RNA to DNA using its magically reverse transcriptase protein.
There are two kinds of HIV, HIV-1 and HIV-2. What is their distribution.
HIV-1: EVERYWHERE
HIV-2: Western Africa
Within HIV-1 we divide infection types into groups. There is O group, N group and M group. Which one is the most common and describe its classification.
M group is the most common (95% of all infections). This group is split into different CLADES (A, B, C, D etc) that we use to classify what strain of HIV is where in the world.
O group: outlier group
N group: not M or O group. I did not make this up.
What clade is most common in North America (and Europe, Australia and South America too)
Clade B.
Because we’re the BEST!
A,C,D in Africa.
C in Asia.
E in the Asian Pacific
What host receptors does HIV bind to?
On the CD4 cell, the CD 4 receptor binds to gp120, and the CCR5 receptor binds to gp41. CCR5 is predominantly affected in the PRIMARY infection.
CXCR4 is the CD4 receptor that is predominantly affected in the progression to AIDS.
Which receptor is more ubiquitously expressed on the CD4 cell, CXCR4 or CCR5?
CXCR4
But remember that the first receptor HIV goes for is CCR5
We always talk about CD4 cells being affected by HIV. What other immune cells are HIV targets?
- Monocytes/macrophages
2. Dendritic cells (aka Langerhans cells in epithelium)
Where does HIV find all the CD4 T cell to infect? What are the main target tissues?
Mucosal tissue: lots of activated CD4+
- Cervix
- Vagina
- Anus
- Rectum
- Foreskin
Once HIV infects the CD4/Macrophage/Dendritic cells in the genital mucosa, what happens next?
These infected cells go to the genital lymph nodes. Here they replicate more and then travel either free or associated with cells through vessels leading to systemic lymphoid replication.
Let’s talk about the genes of HIV and what they code for. Name the 3 most important genes and their products
Gag: codes for nucleocapsid core protein
Pol: codes for reverse transcriptase protease, and integrase
Env: codes for the envelope glycoprotein
Walk me through HIV replication, from first site to entry into the cell. General terms first.
- HIV spots a CD4 cell from across the room
- HIV gp120 binds to CD4 receptor
- gp41 then binds to CCR5
- They binding leads to conformational changes that expose the p41 fusion protein that helps the membranes of HIV and CD4 cell fuse.
- Viral capsid is released into the CD4 cell
- HIV has gained access to the cell. Shit’s bout to go down.
Now HIV is in the cell. WHAT HAPPENS NEXT??
The viral RNA is released and reverse transcriptase is used to make some good old DNA. Viral DNA duplicated to make double stranded DNA. This goes to the nucleus and is integrated into the host DNA by integrase enzyme. Transcription occurs, so now all the viral proteins have been made. You make a new virus and now you’re royally fucked.
Describe attachment and entry of HIV in detail.
- CD4 binds to gp120
- This causes conformational change in gp120 so that it also binds CCR5, and also releases gp41’s fusion protein.
- Gp41’s fusion protein integrates into the host membrane and then folds in on itself. This allows viral entry to occur.
DNA formation. Discuss in detail.
Viral mRNA is made into DNA by reserve transcriptase enzyme. The enzyme starts working at the LTR (long terminal repeat) site. Reverse transcriptase also destroys the RNA after DNA is made. DNA is then duplicated so you’ve got a double stranded helix.
Why does HIV mutate so much?
- Can use either strand of RNA to make DNA
2. Reverse transcriptase lack self-correcting function that our DNA polymerases have.
What protein helps the double stranded viral DNA into the nucleus?
Viral protein R (Vpr) puts the dsDNA in the PIC (preintegration complex) which contains the integrase enzyme and other transport proteins
What exactly does integrase do?
It nicks the viral DNA at the LTR site making “sticky ends” and nicks the host DNA at complimentary sites. Cellular ligase enzyme seals the viral DNA into the host. And now you’re infected with HIV for the rest of your life.
Where on the LTR does TRANSCRIPTION occur? Not reverse transcription! Making mRNA after the HIV is already in the host genome.
The TAR site (tac activated response element). On the viral DNA.
What accessory protein initiates transcription of the host genome?
TAT protein (trans-activator of transcription). This protein has a TAR binding domain which makes sense since that’s where we are starting transcription!
Ok so TAT binds to TAR and then a bunch of other cell cycle proteins join the party so you have this big protein complex on the to-be transcribed DNA. What’s the point?
This complex activates RNA polymerase II, which does the transcribing. Now you’ve got mRNA.
You have to get the transcribed mRNA out of the nucleus so that it can be translated into proteins in the cytoplasm. Remember that this mRNA transcript is made in spliced pieces. What HIV protein helps to transport our HIV transcripts to the cytoplasm.
HIV rev protein binds to RRE (rev response element), which is on many (but not all) HIV transcripts. Rev helps get these suckers out so that HIV can unleash its rath.
So we translate our RNA transcripts into proteins in the cytoplasm. Do the 3 protein we care most about: gag, pol and env, just start doing their job or are they cleaved first?
Env: is translated as gp160 and then cleaved into gp120 and gp41
Pol: translated as a precursor protein with gag and cleaved into its active parts
*Gag: translated as a precursor protein but is not cleaved until it leaves the cell. Since it is cleaved by proteases, this is the site of action for protease inhibitor antiretrovirals.
