Virus tropism & entry Flashcards
Name 4 cellular barriers to virus entry
- glycocalyx (proteogylcans + protein layer)
- plasma membrane
- late endosomal pH
- can only use one high affinity receptors OR a few low affinity receptors
What are the 7 major stages of virus entry?
- binding to cell surface
- lateral movement/diffusion
- activation of signaling
- virus endocytosis/membrane fusion
- penetration
- intracellular transport
- genome uncoating
Name a few ways viruses enter cells – state if this pathway is done by enveloped or naked or both viruses
- env – fusion at the pm
- naked – pore-mediated penetration
- both – endocytosis: RME (clathrin, caveloin, lipid rafts)
name 3 properties that makes a good viral entry receptor?
- ubiquitous expression
- evolutionarly conserved across species
- essential for cell/host survival
what are some common cellular receptors used by viruses?
- sialic acid residues
- cell adhesion molecules, IgSF or integrins (e.g. CD4 and JAM-A)
- PtdSer receptors
when does a measles rash appear post exposure?
14 days
how does measles lead to death among young children?
infects and kills immune cells (including memory cells) – can wipe out preexisitng immunity
what are two reasons why some kids are not vaccinated against measles?
- poor accessibility in developing countries
- vaccine hesistancy (claims that measles vaccine causes autism)
Describe the general features of the measles virus
- (-)ssRNA genome
- enveloped
- replication occurs in the cytoplasm
- MeV P, C, and V proteins block innate antiviral repsonses within HCs
what are the 3 known measles virus entry receptors?
- SLAM/CD150
- MCP/CD46
- PVRL4/Nectin 4
CD46/MCP: what is its normal cellular function, expression, what other pathogens use it as an entry receptor, what MeV strains use it, why is a target of gene therapy/oncolytic virus applications?
- regulator of complement activation
- expressed on all nucleated cells
- pathogens: human herpesvirus 6, adenoviruses, strep pyogenes, neisseria
- strains: vaccine only
- target: in cancer cells CD46 is highly upregulated –> selective and this R is ubiquitous
CD150/SLAM: what does SLAM stand for, which cells is this expressed on, what domains does this R contain, what MeV strains use it?
- SLAM = signaling lymphocyte activating molecule
- expressed on a subset of immune cells: DCs, macrophages, activated T and B cells –> can cause immunosuppression by decreasing circulating T and B cells
- contains Ig-like domains (variable or constant)
- strains: vaccine and wt
Nectin4/PVRL4: which cells express this, what is this a marker of, what do mutations in this receptor cause, what MeV strains use this?
- expression normally restricted to placenta in humans (epithelial cells)
- tumor associated marker for breast, lung and ovarian cancer
- mutations –> ectodermal dysplasia/syndactyly syndrom (webbed hands and feet)
- strains: vaccine and wt – use to get out not in!
describe how MeV receptors dictate disease progression following infection
when using SLAM in immune cells (wt): infects upper respiratory LNs –> trojan horses to LNs
when using Nectin4: MeV dissemination and viremina –> MeV exit via respiratory epitherlium (aersolized)
when MeV enters the respiratory tract how does it enter ICs?
- uses DC-SIGN (measles coR) and SLAM to enter ICs –> specifically DCs and macrophages
- virus attatchement causes increases SMase activity and increased SLAM R clustering
how does MeV enter lymphocytes?
DCs present it to T cells in the LNs
how does MeV exit the body/is coughed out?
infected T cells and DCs are present on the basolateral side of airway epithelial cells and squeeze into the tight junctions where MeV enters the epithelial cells via Nectin 4 and then the virus is apically releases into the lumen and coughed out
what is the major protein decorating SARS-Cov2?
spike (S) a glycoprotein
Briefly describe SARS-CoV-2 entry into cells: endosomal entry and cell surface entry
endosomal entry
- virus binding to ACE2
- internatlization
- endosomal acidification
- cleavage of S2 by cathepsin L
- membrane fusion
- uncoating of viral RNA
cell surface entry
- virus binding to ACE2
- cleavage of S2 by TMPRSS2
- membrane fusion
- unocating of viral RNA
what makes SARS CoV 2 spike different from other beta-coronaviruses?
before release, spike is cleaved into S1 and S2 domains at the furin cleavage site
describe how a SARS CoV2 pseudovirus is made and what this assay would look for? whats the advanatages what are the disadvantages?
- trasnfect HEK293T cells with lentriviral vector-GFP plasmis and spike plasmid –> spike-pseudotypes lentiviral partciles are packaged and releases –> newly infected cells will express GFP –> cannot replicate because no replication machinery in pseudovirus
- looks for cells that can sufficiently intake the virus
- advantages: safety and quanity one round of infection
- disadvantages: only one round of infection, role of other viral proteins
do SARS and COVID enter different or similar cell types?
similar cell types
Describe sars-cov-2 membrane fusion
RBD samples “one-up”/”three-down” conformation –> RBD in “up” conformation binds ACE2 which exposes the S2’ cleavage sight (secondary cleavage via Cathepsin L or TMPRSS2) –> cleavage at the S2’ site releases structural constraints on the fusion peptide (major conformational changes in S2) –> post fusion structure of S2 forms, which brings the cell and viral membranes together, facillitating formation of the fusion pore and virus entry
what does the sars cov 2 virion architecture look like, what is a consequence of this? what consideration does this make for vaccination?
have s1/s2 trimers and just s2 proteins –> body created non-neutralizing Abs to s2 –> should make vaccine to stimulate S1 Abs
what are the two S cleavage sites for TMPRSS2?
S1/S2 and S2’ sites
which cells highly express TMPRSS2?
upper airway respiratory cells
what is the function of hydroxychloroquine?
prevents acidification of the late endosome
what is the function of camostat?
blocks TMPRSS2 protease cleavage
describe a couple of proposed therapeutic treatments for COVID19
- target ACE2 receptors: souble RBC mimic or scFV against ACE2 –> virus cannot bind to ACE2
- target RBD of spike protein: mAb therapy (bamlanivimab)
what is the ancestral lineage of Sars Cov 2? what did this mutate to? what is the advantage of this mutation?
ancestral: D614 –> G614
G614 –> less premature s1 shedding on spike –> –> more spike in one up conformation –> productive viral entry –> March Lockdown
