Intracellular Survival Flashcards
phagocytosis: what is involved in uptake (2)
- microfilament rearrangements
- lead to formation of a phagosome membrane
what does phagocytosis activate
- activation of respiratory/oxidative burst
what host cell enzyme aids in the respiratory/oxidative burst
- NADPH oxidase
respiratory/oxidative burst: NADPH oxidase (3)
- an electron transport chain
- moves from cytosol to the phagosome membrane
- transfers electrons from NADPH in the cytosol across the vacuole membrane
oxygen-dependent killing (3)
- transfer of electrons reduces oxygen (O2) to superoxide (O2-)
- results in productive of reaction oxygen and nitrogen species
- causes damage to DNA, protein, and lipids inside the phagosome
reactive oxygen species (4)
- superoxide
- hydrogen peroxide
- hypochlorite
- hydroxyl radicals
reactive nitrogen species (3)
- nitric oxide
- peroxynitride
- nitrogen dioxide
oxygen-dependent killing: how is superoxide (O2-) produced
- NADPH oxidase converts O2 and NADPH to O2-
oxygen-dependent killing: how is hydrogen peroxide produced
- superoxide dismutase converts superoxide (O2-) to hydrogen peroxide (H2O2) using protons (H+)
oxygen-dependent killing: how are hydroxyl radicals created
- hydrogen peroxide (H2O2) combines with superoxide (O2-) to produce hydroxyl radicals (OH)
oxygen-dependent killing: how is hypochlorite created
- myeloperoxidase converts hydrogen peroxide (H2O2) into hypochlorite (OCl-) using Cl-
oxygen-dependent killing: how are singlet oxygens made
- hypochlorite (OCl-) and hydrogen peroxide (H2O2) combine to form a single oxygen (1O2)
oxygen-independent killing (6)
- acid pH
- lysozyme
- cationic proteins
- bacteriostatic molecules
- acid hydrolases
- fusion with lysosome
oxygen-independent killing: acid pH (2)
- vacuolar ATPase pumps H+ into the phagosome to create a acid pH environment
- affect the bacterial surface
oxygen-independent killing: lysozyme
- dissolves the cell of certain Gram-positive bacteria
oxygen-independent killing: cationic proteins
- bactericidal activity/damages bacteria
oxygen-independent killing: bacteriostatic molecules (2)
- lactoferrin sequesters iron
- vitamin B12-binding proteins sequesters B12
oxygen-independent killing: acid hydrolases
- post-mortem digestion of the microorganism
oxygen-independent killing: fusion with lysosome (2)
- activation of lysosomal enzymes
- acid hydrolases, cationic antimicrobial peptides, and lysozyme
oxygen-independent killing: result (2)
- bacteria are killed and digested
- damage to cell wall, cell membrane, and DNA
normal endocytic events (4)
- early endosome
- late endosome
- fusion with lysosome to create the phagolysosome
- destruction of the bacteria
Rabs
- small GTPases
Rab5
- early endosome marker
Rab7
- late endosome marker
LAMP1 (2)
- lysosomal associated membrane protein
- phagolysosome fusion marker
what tools can we use to see where the phagosome is located in the pathway (3)
- western blot
- IH
- IF
bacterial phagosome survival mechanisms (4)
- failure to trigger oxidative burst by inhibiting phagosome acidification
- inhibit/stall the fusion of the phagosome with the lysosome
- survival within the phagolysosome
- escape from the phagosome
legionella pneumophila
- resulting illness
- spread
- demographic
- symptoms
- intracellular survival
- causes Legionnaire’s Disease
- spread by water droplets/aerosols
- usually found in elderly or smokers
- cough, pneumonia, high fevers
- survives and grows in macrophages
how does legionella pneumophila survive in macrophages; basic steps (6)
- legionella pneumophila are taken up into a phagosome
- phagosome does not become acidified or fuse with the lysosome (fusion may be delayed)
- instead, phagosome is surrounded by ER studded with ribosomes
- bacteria multiple in the phagosome
- the phagosome ruptures, releasing the bacteria into the cytoplasm to further replicate
- the bacterial lyse the host cell and escape
how does legionella pneumophila release effectors into the host cyotsol
- it delivers 280 proteins to the cytosol using the Dot system, a T4SS
what is the name of the phagosome that Legionella is found in
- Legionella containing vacuole (LCV)
how does Legionella achieve early diversion of the endocytic pathway (3)
- LCV membrane resembles the ER
- reminiscent of an autophagous vacuole (autophagy)
- does not contain Rab5 or Rab7 markers, and LAMP1 marker is delayed
autophagy (2)
- induced when cell undergoes starvation
- mechanism for recycling proteins
how does Legionella pneumophila stall phagosome maturation for several hours (3)
- LCV has Rab1-GTP on membrane, a protein associated with autophagosomes
- Legionella proteins LidA and DrrA ensure that Rab1 remains in GTP-bound state
- results in delay of phagosome maturation and delayed fusion with lysosome
what occurs while Legionella delays the phagosome maturation (2)
- legionella pneumophila undergoes a developmental cycle
- transformed bacterium is able to survive within the phagolysosome environment
how does Legionella continue the phagosome maturation and allow for lysosomal fusion (3)
- Legionella secretes LepB protein
- LepB allows for conversion of Rab1-GTP to Rab1-GDP
- LCV is now able to fuse with lysosomes and LAMP1 appears on the LCV membrane
chlamydia
- type of pathogen
- varieties (3)
- obligate intracellular pathogens
- C. trachomatis
- C. pneumonia
- C. psittaci
Chlamydia trachomatis (4)
- disease type
- early symptoms
- acute symptoms
- long-term symptoms
- sexually transmitted disease
- early stages are mild with few symptoms
- painful urination, discharge from vagina/penis
- can lead to pelvic inflammatory disease, infertility, and blindness
Chlamydia pneumonia (2)
- symptoms
- linked to
- causes pneumonia
- linked to atherosclerosis
Chlamydia psittaci
- causes psittacosis in birds
what is the name for the phagosome that contains Chlamydia
- Inclusion
how does Chlamydia generally survive inside the Inclusion (2)
- it has a bi-phasic developmental cycle
- cycle takes place entirely within the Inclusion
bi-phasic developmental cycle of Chlamydia (2)
- elementary body (EB): environmentally stable form that can infect cells
- reticulate body (RB): intracellular replicative form
life cycle of Chlamydia (5)
- 0-2 hours: internalized EBs fuse to form an Inclusion
- 2-6 hours: EBs differentiate into RBs
- 12-24 hours: RBs replicate by binary fission and peak in numbers as the Inclusion matures; RB juxtaposed to Inclusion membrane
- 24-40 hours: RBs differentiate back to EBs
- 48-72 hours: lysis/release occurs and EBs exit
Chlamydia: aberrant body (2)
- RBs may transition into aberrant bodies during stress and remain dormant
- aberrant bodies are reactivated in RBs when stress is reduced and continue through cycle
how does Chlamydia release effectors into the host cytoplasm
- releases multiple effectors using a T3SS
Chlamydia: dynein-dynactin complex
- causes trafficking of Inclusion toward ER
Chlamydia Inclusion properties (4)
- no Rab5 or Rab7 markers on the membrane
- Rab4, Rab11, Rab1 markers found on secretory vesicles
- found in peri-Golgi area of the cell
- Chlamydia fuses Inclusion with vesicles in secretory pathway and stalls/delays secretion until cell lyses
Chlamydia: Inc
- bacterial Inclusion protein that prevents fusion with lysosomes and promotes interactions with recycling endosomes for iron acquisition
Listeria monocytogenes and Shigella flexneri: escape from phagosome
- although Listeria is gram positive and Shigella is gram negative, they have the same mechanism for survival/escape from phagosomes
Listeria monocytogenes
- bacteria type
- growth and location
- type of illness
- symptoms (2)
- gram positive, non-spore former
- grows well at 4C (fridge) and is often found in unpasteurized milk and milk products
- food-borne illness
- causes flu-like symptoms in healthy individuals
- can be fatal for fetus, newborns, immunocompromised individuals, elderly, and pregnant women
Listeria monocytogenes: host cells (2)
- infects a variety of cells
- monocytes, macrophages, epithelial cells, etc
how does Listeria monocytogenes invade cells (2)
- invades via InlA/InlB using zipper-mediated uptake
- following uptake, it is found in an early endosome
how does Listeria monocytogenes escape the phagosome (2)
- endosome containing Listeria becomes more acidic
- at low pH, Listeria toxin Listeriolysin O (LLO) and phospholipase C gets activated and lyses the phagosome membrane
how does Listeria monocytogenes escape the host cell after phagosome escape (2)
- actin tails form at one end of the bacterium in the cytosol
- serve to propel bacteria throughout the cytosol and to adjacent cells
what is the process of Listeria monocytogenes escaping the host cell called and what is it mediated by (2)
- actin nucleation
- protein ActA
ActA (4)
- nucleates actin polymerization
- asymmetry (only expressed at one pole)
- initiates movement
- increased velocity due to recruitment of host proteins profilin and VASP
what occurs after Listeria is propelled into adjacent cells (3)
- formation of phagosome with a double membrane in adjacent cells (one from original cell and one from adjacent host cell)
- double membrane is lysed by Listeria Proteins called Phospholipases (PlcA, PlcB, PlcC) and LLO
- cycle continues
phagosome escape: Shigella flexneri
- Shigella employs the same strategy as Listeria, but uses different proteins for phagosome escape
Listeria proteins: Bacteria taken up in vacuole in host cell (2)
- InlA
- InlB
Shigella proteins: Bacteria taken up in vacuole in host cell (2)
- IpaB
- IpaC
Listeria proteins: Vacuole is lysed; bacterium escapes into cytosol and replicates (3)
- LLO
- PlcA
- PlcC
Shigella proteins: Vacuole is lysed; bacterium escapes into cytosol and replicates (2)
- IpaB
- IpaC
Listeria proteins: Actin tail formation; intracellular movement; cell to cell spread
- ActA
Shigella proteins: Actin tail formation; intracellular movement; cell to cell spread
- IcsA
Listeria proteins: Lysis of double membrane vacuole in new host cell (3)
- LLO
- PlcA
- PlcB
Shigella proteins: Lysis of double membrane vacuole in new host cell
- IcsB
