Lecture 5 Flashcards
Where does Helicobacter pylori colonize?
The gastric Mucosa
What occurs due to infection by H.pylori?
Stomach Ulcers; Gastritis
How does H.pylori achieve this?
Secretion of Urease; which hydrolyses Urea to ammonia, creating micro environments at higher pH. Modifying the environment to allow its own growth
What other pathogens have urease? What do they use it for?
Proteus mirabilis and Klebsiella use urease when urea is the carbon source. Presence of urea and lack of nitrogen respectively
What are PAMP’s?
Pathogen Associated Molecular Patterns Generic molecules that will generate an innate immune response
Give some example PAMP’s
Lipid tail of LPS on Gram -ve bacteria recognised by TLR-4 Peptidoglycan of gram +ve bacteria recognised by TLR-2
What effect does a capsule have on a bacteria ability to evade the innate immune system
Physical prevention against ingestion by macrophage
How does salmonella enterica use its capsule?
Stops neutrophils being able to use chemotaxis to extended towards the bacterium
Give one way in which pathogens can use host-like compounds to hide?
Presenting sialic acid makes the pathogen appear as ‘self’
What three things can lead to a population of cells being different to each other?
Stochastic variation, antigenic variation and phase variaiton
What is phase variation?
Within a population a gene can be on/off and hence cause a difference in the population
What is antigenic variation?
Antigenic variants of each protein exist, and each cell is not identical due to ability to express each variant
How is antigenic variation used to evade the immune system?
Once the immune system is able to elicit a sufficient response to one antigenic variant and remove it from the population, another antigenic variant can grow into the space now available and the immune system has to start again. This is repeated for each antigenic variant
What type of proteins commonly show antigenic variation?
Cell surface structures and proteins
What type of plasmids exist?
Expression plasmids and storage plasmids
Why are storage plasmids important in antigenic variation?
Hold the protein variants. These loci can undergo recombination into the expression plasmid
Give some examples of antigenic surface structures
Flagells, outer membrane proteins, LPS and fimbriae
What is the difference between transcriptional and translational fusion?
Transcriptional fusion you will tag a reporter after a promoter of interest and will be able to see when that promoter is active and hence when the downstream gene is being transcribed
Translational fusion you tag the protein of interets and can see where, and how much of, the protein is actually in the cell
What effect can short sequence repeats have on DNA replication?
May cause DNA polymerase to make a mistake incorporating too few or too many of the repeated nucleotide
How can short sequence repeats then have transcriptional effect?
- The activator may not be able to make contact with the RNAPolymerase
- Changes to the spacing between the -10 and -35 locations can stop RNA polymerase being able to bind
- Stability of the RNA may be compromised
- Missense or nonsense mutation if happens in coding region
What is classified as a short sequence repeat?
Mono-, di-, tri- or tetra-nucleotide repeats between 30 and 50 bp long
What causes site-specific recombination?
Inverted repeat recombinase recognition sequences either side of DNA sequence can be recognised by a recombinase and the DNA can be inverted.
Outline an example of site-specific recombination
Type 1 fimbriae
DNA inversion in Fim operon
Controlled by site-specific recombinases: FimE and FimB
FimE promotes ON to OFF transition
FimB promotes both directions equally
Outline an experiment which investigated if phase variation is a virulence factor
E.coli on murine bladder model
Locked ON and locked OFF Type 1 Fim
Locked ON survived as well as wild type, but locked OFF did not
Doesn’t prove that phase variation is virulence factor only that the fimriae was important for survival
How can phase variation been controlled at the non-DNA sequence level?
DNA Methylation
What protein is imporant in DNA methylation?
Deoxyadenosine methylase - which methylates adenine of GATC sequence
What are the substares of DAM?
Both unmethylated and hemimethylated DNA
Why is the methylation irreverisble in E.coli?
There is no demethylating enzyme in E.coli
How is DAM activity regulated?
Regulatory protein binding blocks DAM access
But once DNA is methylated the regulatory protein can no longer bind and DAM can continue to methylate
How can DNA switch between methylated and unmethylated?
During DNA replication
Outline phase variation by Lrp and DAM
Lrp can bind to two sites on Pap operon - when they are not methylated
Binding to one site due to other site being methylated causes pilin production to be off
Binding to other site due to first site being methylated causes pilin production to be on
How is a positive feedback loop involved in the Pap operon phase variation?
Binding of Lrp to site which causes pilin production requires PapI
PapI is made due to the binding of PapB, and CAP, which is made due to Lrp binding to correct site
How can sRNA be found to be sequenced?
Pull down of Hfq- a factor associated with sRNA for stability
Who wrote the paper from the lecture?
Khandige
What effect was Hfq shown to have in bladder cell infection?
Knockout of Hsq lead to less adhesion and invasion of cells
