Quorum sensing Flashcards
(6 cards)
LuxI/LuxR paradigm for gram neg quorum sensing in Vibrio fischeri?
LuxI enzyme produces HSL autoinducer, in HCD situations concentration high enough to activate intracellular LuxR which acts as transcriptional regulator, binds to Lux/luciferase promoter region. Also activates transcription of LuxI –> positive feedback loop amplification –> enhances synchronicity of bioluminescence
Generic peptide based quorum sensing mechanism 4 genetic/protein components?
Peptide structural gene
Peptide transporter (exporter) (which also cleaves peptide)
membrane bound peptide receptor (histidine protein kinase)
Activates by reversible phosphorylation: Cytoplasmic DNA binding regulator (response regulator)
2 areas of particular clinical significance of Pseudomonas aeruginosa (opportunistic gram negative pathoegen):
Burns victims: forms green pigment pyocyanin (a toxin)
CF patients: key infection in CF: forms biofilms that stimulate mucous secretion, clog up lungs
Parallel Acyl-HSL systems in Pseudomonas aeruginosa?
and what is meta-bromo-thiolactone (mBTL)?
Las and Rhl, HSL systems.
LasI produces HSL autoinducer, LasR receptor activates virulence factors for early stages infection as well as RhlI, a synthase which makes its own HSL autoinducer that activates RhlR above threshold concentrations. (which produces late stage virulence factors like Abx against competing species)
(mBTL is a quorum sensing inhibitor: competes with the HSLs for binding LasR and RhlR.)
Peptide based quorum sensing system in Staphylococcus aureus? interplay between different strains?
Staphylococcus aureus Accessory gene regulator, agr, signalling system.
Encoded in variable region: AgrD is strain specific peptide structural gene. AgrB is strain specific transporter (also cleaves). AgrC AIP receptor (histidine protein kinase)
AgrA is only consistent component, it is response regulator protein —> DNA binding to P2 and P3 diverging promoter regions.
P2 leads to transcription of agr system.
P3 leads to transcription of regulatory RNAIII.
RNAIII is the effector which controls 100s of genes! (at level of translation initiation)
How does the Staphylococcus agr system effector, RNAIII, regulate gene expression?
At the level of translation iniation, it binds mRNA close to the ribosome binding site.
Either freeing Ribosome binding site (Shine-dalgarno sequence): promoting translation of Alpha-haemolysin (diagram)
Or inhibiting translation by blocking site (e.g. rot regulator) or promoting degradation ribonucleases.
