Pathogens and Intracellular Membranes #2 Flashcards
(17 cards)
1
Q
what are the steps of salmonella invasion?
A
- salmonella cells attach to the intestinal epithelium by means of adhesins.
- invasion of bacteria follows, engulfment is mediated by virulence factors (molecule produced by pathogen, enhancers its ability to cause disease in host)
- once inside the cytoplasm, salmonella is localized within salmonella containing vacuole (SCV), where it replicates.
- the SCVs transcytose to baso-lateral membrane and release the internal cells to the submucosa.
2
Q
what secretion system does salmonella use?
A
- secretion III system
-> injection of proteins into the cytoplasm of enterocytes.
3
Q
what type of membrane systems does bacteria have?
A
- bacteria lack internal membrane system (like in the secretory pathway of eukaryotic cells)
- instead specialized machinery to translocate proteins through their plasma membrane
4
Q
what is the different between gram (+) and (-) bacteria?
A
- (-) have two membranes
- (+) have one membrane
5
Q
what is the function of secretion system III and IV?
A
- they can deliver proteins through bacterial membranes but also through endosomal or plasma membrane of a eukaryotic cell.
- more elaborate systems -> specific bacteria groups.
6
Q
salmonella containing vacuoles (SCVs)
A
- incorporate into early endosome pathway.
- bacterium encodes for effector proteins that prevent SCV from fusing to lysosomes (to prevent them from being destroyed)
effector protein functions:
1. keep elevated and prolonged levels of PI3P. this blocks production of PI(3,5)P2, important for vacuole progression.
- SCV acquires Rab7, links SCV to cell’s transport machinery (dynactin-dynein), moves it closer to nucleus.
- SopD2 interfers with above - removes RILP protein that aids Rab7 from interacting with other proteins needed to eventually fuse with lysosome.
- resulting SCV has early and late characteristics - arrests in late maturation stage.
7
Q
what secretion system does Legionella Pneumophila contain? what is its function?
A
- contains IV secretion system
- can deliver proteins through plasma membrane of a eukaryotic cell
- after phagocytosis, Type IV secretion injects protein that causes Rab5 to be ubiquitinated and removes from endosomal membranes, without recruiting Rab7.
- result is abnormal early endosome which cannot mature, but which can support bacterial growth.
8
Q
what is the life cycle of a virus?
A
- entry into cell
- duplication of genetic material and alterations to host cell
- ‘early into cell’
- construction of ‘virus factories’ - production of new virus particles
- late phase - new virus particles leave cell
9
Q
what are the characteristics of enveloped virus?
A
- examples: reovirus (dsRNA), adenovirus (dsDNA), poliovirus ((+))-ssRNA), T4 bacteriophage.
- any kind of genome
-virus particle consists of protein complex with nucleic acid.
- enters cell by endocytosis.
- release of new virus particles may require the cell to lyse (break open) - cell dies - virus have to wait until cell dies before it can spread to other cells.
10
Q
what are the characteristics of enveloped virus?
A
- examples: HIV (retrovirus with RNA) , Herpes (DNA virus). influenza ((-)-strand ssRNA), Sars-Cov2 ((+))-strand RNA.
- any kind of genome
- virus has lipid bilayer as envelope
- normally derived from cellular membranes - can be destroyed by detergent
- internal part of the virus (within the envelope) consists of a protein complexed with nucleic virus.
- integral membrane proteins cross the envelope.
- may recognize proteins on the target cell and can permit direct fusion of virus with cells membrane or fusion after endocytosis .
11
Q
how do non-enveloped viruses enter the cell?
A
- must disrupt the endosome membrane to get their nucleic acid into the cytoplasm.
12
Q
replication cycle of a non enveloped virus - poliovirus
A
- virus binds to receptor on cell surface and is endocytosed.
- endocytosis & exposure to low endosomal pH.
- poliovius inject their RNA genome into the cytoplasm.
- viral RNA is threaded through a pore made in the endosomal membrane by a viral protein.
- RNA binds to ribosomes and is translated, producing viral proteins, including RNA-directed RNA pol.
4 Once viral replication begins, viral replication organelles are created that are associated with ER membranes.
- ribosomes modified so they preferentially translate viral mRNA.
- most translation of cellular proteins stop .
13
Q
what associates with the viral RNA produced in the replication cycle of poliovirus ?
A
- viral structural proteins (VP1, VP2, VP3, VP4) associated with the viral RNA in the cytoplasm to form virus particles.
- virus particles can be released when cell dies, or process where multiple virus particles are enclosed in phosphoserine-rich membrane.
- the phosphoserine-rich membrane is enclosed in an autophagosome structure - fuses with plasma membrane and releases phosphorich vesicle - while infected cell is still alive.
- this vesicle can be endocytosed by adjacent cell, resulting in its infection.
14
Q
how do enveloped viruses enter the cell?
A
- integral membrane proteins in the envelopes of enveloped viruses drive fusion with plasma membrane of target cells
- some cases: immediate fusion with cell surface
- other cases, enveloped viruses only fuse with membrane after exposure to low pH in endosomes (early endosomes)
- integral membrane proteins found in the virus’ envelope must use the secretory pathway to reach the destination where virus budding occurs.
15
Q
replication cycle of enveloped virus: Sars-Cov-2 entery into cells
A
- spike (s) protein on a virus particle binds to ACE2 receptor at cell surface.
- this triggers conformational change in S, causes virus envelope to fuse with cell’s membrane.
- dependent on variant, virus may fuse directly at cell surface (delta) or be endocytosed and fuse with endosomal membrane (omicron)
- fusion results in entry of entire nucleocapsid including viral RNA into cytoplasm.
- genome of SARS-CoV-2 virus can bind directly to a ribosome and be translated.
- Sars-Cov2 reorganizes ER membrane to sheild viral RNA during replication.
16
Q
usually, budding of many enveloped viruses is very
simple. explain the process
A
- ‘nucleocapsid’ composed of proteins associated with viral nucleic acid (DNA or RNA) assembles in cytoplasm.
- one or more viral, integral membrane ‘envelope’ proteins are synthesized and translocated to ER. (use secretory pathway normally and reach the cell surface)
- viral nucleocapsids bind to cytoplasmic domains of env. proteins at the cell surface - leads to virus budding.
17
Q
sars-cov-2 budding isnt simple - what happens?
A
- bud into lysosomes
- lysosomal pH is modified to be less acidic such that lysosomal enzymes are inactive
- ion channel encoded by virus may be responsible for deacidifying endosomes
- means that envelope proteins of sars-2-cov2 must be targeted to endosome/lysosome system. - buds into multiple intracellular membranes including ERGIC/VTCs.
