I&I B7/8

HIV, Arboviruses I & II, Ebola

Describe the structure of the HIV genome

2x single stranded (+)ssRNA encoding 9 genes that have overlapping sequences

What structural features does HIV have? (4)

Nucleocapsid

Capsid

Matrix

Envelope

What proteins does HIV have a) on its surface envelope and b) inside?

a) gp120, gp41

b) Reverse Transcriptase, Integrase, Protease

HIV transmission routes

• Sexual contact

• Intravenous drug use

• Blood transfusions

• Mother to child transmission

HIV infection life cycle (10 steps)

1. CD207 on DCs binds to gp120 on HIV

2. DCs migrate to draining Lymph nodes

3. Binding of HIV gp120 to cell surface protein CD4

4. conformational change in gp120

5. Binding of HIV gp41 to a cellular co-receptor (CXCR4 or CCR5)

6. Formation of six-helix bundle

7. Fusion of virus envelope & plasma membrane

8. Release of NC into cytoplasm

9. HIV integration and replication in host genome

10. budding and release

What functions does reverse transcriptase (in HIV) have? (3)

RNA dep DNA pol activity

RNase H activity: cleaves RNA from RNA:DNA hybrids.

DNA dep DNA pol activity

Process of reverse transcription of the HIV genome (8)

1. -ve DNA synthesis is initiated using cellular tRNA annealed to the 18-base sequence Primer Binding Site

2. RNA strand of the RNA:DNA duplex is degraded by RNase H of RT.

3. First strand transfer: newly formed DNA —^{R sequences}→ 3′ end of the viral genome

4. -ve DNA synthesis + RNase H digestion of all template RNA except polypurine tract (PPT)

5. PPT is used as a primer for second strand DNA synthesis.

6. RNase H removes the tRNA and the PPT RNA.

7. Second strand transfer: annealing of the newly formed PBS DNA (second strand) to the PBS DNA from the first strand.

8. Completion of second strand synthesis → linear DNA duplex with LTRs at both ends

Integration of HIV DNA (5 steps)

1. Linear HIV DNA enters nucleus

2. HIV integrase: Circularisation of linear DNA

3. “ : Cleavage of terminal dinucleotides

4. “ : Single-stranded nick & end-joining to host DNA

5. “ : Ligation into host DNA

What is a well known example of a) host protein that is a target for a certain b) HIV protein and c) what is the outcome?

a) APOBEC3G

b) Vif

c) poly-ubiquitination of APOBEC3G→ protease

What kind of protein is APOBEC3G?

cytidine deaminase: C→U in the ss DNA substrate

TRUE OR FALSE: HIV can establish reservoirs in latently infected cells with an integrated viral genome

TRUE

HIV reservoirs can exist in…(4)

Central nervous system

Gastrointestinal tract

Genital tract

Lymph node

Describe the genome of ebola (+ gene products)

Negative-stranded RNA linear genome encodes for 7 proteins:

• NP: Nucleoprotein

• VP30: Minor nucleoprotein

• VP35: Polymerase complex protein

• VP40: Matrix

• GP + sGP: envelope glycoprotein, secretory glycoprotein

• L: RNA dep RNA Pol

• VP24: Inhibits STAT1 nuclear transport

How is ebola transmitted?

• broken skin or unprotected mucous membranes

• Contact with infected animals

• Direct contact with body fluids

• Hand-to-eye contact

• potentially Inhalation of aerosol particle

• Sexual transmission

ebola target cells (6)

Monocytes

Macrophages

Dendritic cells

Hepatocytes

Endothelial cells

Epithelial cells.

Ebola infection life cycle (11 steps)

1. GP binds to TIM-1

2. Receptor mediated endocytosis

3. Cathepsins L and B perform sequential proteolytic cleavage on GP1 inside endosome

4. GP1 binds to NPC1

5. Exposure of GP2

6. Fusion of virus membrane with the endosome

7. Release of nucleocapsid

8. Genome replication

9. mRNA translation using host ribosome

10. assembly of nucleocapsid and association with matrix and envelope proteins

11. cytopathic release by budding

How can ebola evade IFN action? (3)

VP35 protein: suppresses the activation of PKR by ISGs (no translation→ apoptosis), suppresses the activation of RIG-I /induction of downstream IFN genes.

VP24: blocks STAT1 activation of ISRE

How can ebola evade antibody action?

deploy sGP to decoy Ab responses

The GP gene of ebola codes for … proteins which are produced by…

The GP gene of ebola codes for 3 proteins which are produced by editing of transcript

How can ebola improve its cellular uptake? (2)

• attached antibodies mediate attachment to host cell FcR

• C1q component of the complement system binds to antibody associated with ebola

What causes symptoms of haemorrhagic fever in ebola? (2)

hepatocytes infected; the liver produces coagulation factors

endothelial cells infected; cytopathic effect and damage to the endothelial barrier → loss of vascular integrity

TRUE OR FALSE: All arthropod borne (arbo-) viruses are RNA genome

TRUE

How are arboviruses transmitted between arthropod and mammal/bird host?

through blood transfer

What are the hosts of Ross River virus?

host and vector generalist—many many!

Describe the structure of Ross River Virus

icosahedral nucleocapsid with envelope embedded with E1 and E2 glycoprotein

RRV symptoms

flu like, but can cause chronic arthralgia

What produces Type 1 interferons upon stimulation with alphaviruses?

TLR 3 & 7