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53 Cards in this Set
- Front
- Back
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What is required for H. pylori colonization of the gastric mucosa?
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Flagella
Urease: neutralize acidic pH of stomach Adhesins: stick to epithelial cells |
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What does the chronic and limited inflammatory response cause?
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Disrupts epitehlium
Induces tissue damage |
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What is VacA?
What does it do? |
Vacuolating cytotoxin
-Encodes a secreted ptn that induces vacuole formation inf host epithelial cells -Promotes apoptosis |
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How many different forms of vac A are there?
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4 (m1/2, S1,2)
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What do these 4 types result in?
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Homologous recombination among vacA alleles from diffferent strains
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What does type s1/m1 do?
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Extensive vacuolation of many different cell types (not just epithelial cells)
-Most pathogenic form of vacA |
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What does type s1/m2 do?
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Causes detectable vacuolation in a limited range of cells (mainly epithelial cells)
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Why are vacA molec of s2 type inactive in asays for vacuolating cytotoxicity?
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Have a 12 aa insertion in signal peptide
-> but can still contribute to the bacteria's virulence in vivo through additional activities |
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What is VacA synthesized as?
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140 kDa protoxin
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How is VacA transported in the periplasm?
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Sec-dependent process
Cleavage of the signal peptide |
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Describe the autotransport activity (Type V secretion) of vacA
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C-terminal autotransporter domain (B-barrel) inserts into the OM and exports the toxin outside of the bacterial cell (passenger domain passes through the B-barrel)
Proteolytic cleavage and release of mature toxin (not all autotransporters can self cleave, but this one can) |
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Where is the mid region located?
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in the p55
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What is the structure of p55 vacA?
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B-helix structure
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How many toxins is the VacA toxin made up of?
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12 subunits (dodecamer)
-> 2 layers of 6 arms p33 on the inner part of the arm, p55 on the outer part |
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What is the proposed mechanism of action of VacA?
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VacA binds to sphingomyelin at the cell surface and is internalized
VacA forms ANION-selective channels in the mb of the late endosomes -Get increased intraluminal [Cl-] (Cl- goes into the vacuole) -vacuolar ATPase acitvity increases to compensate for influx of Cl- and there is an influx of H+ ->Get reduction in intraluminal pH (more acidic) -Mb permeant weak bases like Ammonia diffuse into the late endosomes and become proteated and trapped in these compartments -Osmotic swelling of the compartments lears to cell vacuolation |
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What are other putative actions of vacA? (3)
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1) vacA involved in adhesion (not secreted)
Interacts with receptors on host cells and causes proinflam signals -> Causes cytokine secretion 2) Vac A gets to mitochondrial mb and alters it, releasing Cyt C ->causes cell apoptosis 3) Acts on T-cells, inhibits their proliferation To do this, vacA has to go through 2 epithelial cell .: it must diss't CagA disrupts the tight jcts , allowing vacA to pass through and act on T cells in the mucosa, where it inhibits their activation |
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Describe the cag pathogenicity island?
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40 Kbp
30 genes ->12 genes encode a T4SS |
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What does the CagA gene encode?
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146-kDa CagA ptn
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How many effector ptns does H. pylori inject into the host through its T4SS?
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only 1
CagA (compared to in T3SS where 10-15 effector ptns are usuallt secreted) |
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What does the T4SS look like?
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Pilus like structure
Crosses inner and outer mbs of bacteria Inserts into host cell mb Injects CagA into cytosol |
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What is a T3SS structurally similar to?
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Flagellar apparatus
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What is a T4SS structurally similar to?
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Conjugative apparatus
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Which species has both type 3 and 4 SS?
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Bordetella bronch..
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What secretion systems does H. pylori have?
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Only T4SS
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What SS does Salmonella have? Why?
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2 T3SS's
1st: go through eppithelium, trigger invasion 2nd: once in macrophage, inject into cytoplasm from host vacuole , some ptns |
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What are the fcts of T4SS in:
E. coli? |
Conjugative transfer of DNA
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What is the fct of T4SS in Bordetella persussis?
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Export of pertussis toxin (PT) in the extracellular env't
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What is the fct of T4SS in H. pylori?
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Inject virulence factor (CagA)
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What is the fct of T4SS in Agrobacterium tumefaciens?
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Transfer of Ti PLASMID DNa from the bacteria to the plant cell nucleus
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What is the fct of T4SS in Rickettsia, Legionella and Brucella?
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Delivery of effector moleculees to the cell cytoplasm or to the vacuolar mb
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Describe the interaction btw CagA and Gastric epithelial cells
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Translocated CagA ptn localizes to the inner surface of the plasma mb
CagA is then P on tyrosine residues by Src family tyrosine kinases |
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Where does the Src family P CagA?
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EPIYA motif
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What are the 4 EPIYA sites?
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EPIYA-A/B/C/D
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What form does CagA take in western H. pylori strains?
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EPIYA -A and EPIYA-B, followed by 1-3 EPIYA Cs
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What form does CagA take in eastern H. pylori strains?
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Similar to western, except has only 1 EPIYA-D (not C's)
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Which strain is more likely to cause disease?
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Eastern strain
Causes greater activation of CagA Higher incidence of gastric cancer |
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How does CagA activate SHP2?
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P of CagA promotes its interaction with SH2 domains of the ptn tyrosine phosphatase SHP2
This causes conformation change in SHP2 that stimulates its phosphatase activity |
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What can activated SHP2 induce?
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Activated SHP2 induces extracellular signal regulated kinase (ERK) through Ras-dependent and independent mechs
(works on kinase paths) |
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Which EPIYA has stronger SHP2 binding? C or D?
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EPIYA-D
this is why it has a higher incidence of gastric cancer |
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What does SHP2 cause, as a result of CagA induced activation?
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Abnormal mitogenic signalling
Hummingbird phenotype Cell scattering |
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What is the hummingbird phenotype?
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Cell elongation
Followed by cytoskeletal rearrangements -> the more P, themore binding of SHP2, the more the hummingbird effect |
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What happens once CagA deregulates SHP2?
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Induction of abnormal proliferation of gastric epithelial cells
->leads to gastric ulcers and eventually gastric carcinomas |
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How can H. pylori inhibit epithelial cell apoptosis?
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CagA dependent manner
(VacA and CagA have opposing effects on host cell apoptosis) |
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What is required to transfer CagA into host cell?
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CagL (ptn on the surface of the secretion apparatus)
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Where does CagL bind?
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Host cell integrins (a5B1)
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What mediates this interaction?
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RGD sequence on CagL
(this sequence specifically binds integrins) |
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What else can CagL do?
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Stimulate integrin mediated signalling (ex: activation of FAK (focal adhesion kinase) and Src family)
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Why is CagL important?
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Ensure P of CagA and .: its activation
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How is CagA transfered into host cells?
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H. pylori synthesizes all the ptns needed to form T4SS
CagL secreted and interacts with the a5B1 ptn CagA can then go in -Whole process take ~90 min |
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What else can the T4SS inject into the host, other than CagA?
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small pieces of p/g
(including the GM-meso-DAP rec'z by NOD1, the dipeptide in the p/g in G- bacteria) |
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What is the purpose of this?
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Engagement of Nod1 leads to NF-kB activation and inflammation
Injecting p/g into the host cell keeps level of inflammation low |
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Can T3SS deliver PAMPs like this into the cytosol of the host?
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Yes
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Why does the bac want to keep only low levels of host inflam?
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Low levels over many years leads to chronic inflammation
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