Virus tropism & entry Flashcards
(30 cards)
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
