lectures 7-8

What is a two-component regulatory (TCR) system?

System that detects external signals and regulates bacterial responses

What are the two main components of a TCR system?

Sensor kinase - detects signals

Response regulator - regulates transcription

How does the sensor kinase work?

Undergoes trans-autophosphorylation on a histidine residue using ATP

What happens after phosphorylation of the sensor kinase?

Phosphate group is transferred to an aspartate residue on the response regulator, activating it

What is the role of response regulators?

Bind to DNA to regulate transcription or interact with cellular targets

What completes the regulatory loop in TCR systems?

A phosphatase removes the phosphate from the response regulator to reset the system

Are TCR systems present in all organisms?

No - found in bacteria, archaea and some eukaryotes but not in animals

What is vancomycin? What kind of bacteria can it be used against?

Glycopeptide antibiotic - effective against

What does the VanS/VanR TCR system do?

Regulates vancomycin resistance by altering peptidoglycan synthesis to prevent antibiotic binding

How does the VanS/VanR system detect vancomycin?

VanS - senses vancomycin and autophosphorylates, transferring the phosphate to VanR

VanR - activates gene expression for resistance

How does vancomycin work?

Blocks transpeptidation by interacting with terminal D-Ala D-Ala of lipid II

How does the VanS/VanR TCR system create resistance against vancomycin?

1. VanR activates gene expression at vanSR and vanHAX promoters

2. These promoters encode proteins that modify the lipid II molecule:

3. D-Ala D-Ala dipeptide removed and replaced with D-Ala D-lactate

4. Vancomycin can no longer bind and crosslinks can still occur

What does the EnvZ/OmpR respond to?

Osmolarity changes

How does the EnvZ-OmpR system work?

1. Sensor kinase: EnvZ, undergoes trans-autophosphorylation on His residue

2. Response regulator: OmpR, phosphate group transferred from EnvZ His to OmpR Asp residue

3. OmpR-P regulates expression of porin genes OmpC and OmpF

How does osmolarity affect gene expression?

Osmotic conditions control the ratio of EnvZ phosphate:kinase activities which determines how much phosphorylated OmpR is produced

Regulation of gene expression by EnvZ-OmpR system - low extracellular osmolarity

Low extracellular osmolarity (dilute environment):

1. Low OmpR

2. Activation of OmpF trancription

3. more ompF porins in outer membrane - these are larger for higher diffusion

Regulation of gene expression by EnvZ-OmpR system - high extracellular osmolarity

High extracellular osmolarity (concentrated environment)

1. High OmpR

2. Activation of OmpC

3. transcription

4. More OmpC porins in the outer membrane - these are smaller for less diffusion, prevents cell dehydration

What is the PhoQ/PhoP system?

TCR system in Salmonella that remodels the outer membrane to resist immune defences

What is quorum sensing?

Mechanism in bacteria to assess population density and respond appropriately

What are the types of quorum sensing signals?

Gram-negative - N-acyl homoserine lactones (AHLs)

gram +ve - peptides

What is competence in bacteria? What is it induced by?

The ability to be transformed, induced by CSP

Mechanism by which cells are made competent

1. ComC encodes CSP

2. CSP is processed and exported by ComAB

3. this is sensed by the TCR ComDE; ComD as sensor kinase and ComE as response regulator

4. ComE-P induces expression of ComX which activates a set of genes to produce competent cells

LuxI/LuxR system in Vibrio fischeri

LuxI - synthesises AHL signal

LuxR - detects AHL, activating bioluminescence genes

LasI/LasR and RhII/RhIR systems in Pseudomonas aeruginosa

LasI and RhII - synthesise AHL signal

LasR and RhIR - detect AHL, controlling gene expression for genes involved in biofilm development, antibiotic resistance etc

TraI/TraR in Agrobacterium tumefaciens

TraI - synthesises AHLs

TraR - detects AHLs, regulates transfer of oncogenic Ti plasmid to plant cells

TraR - detects AHLs, regulates transfer of oncogenic Ti plasmid to plant cells

What are the three quorum sensing pathways in Vibrio harveyi?

1. HAI-I pathway

2. CA-I pathway

3. AI-2 pathway

CA-I pathway

What signal is used? What kind of communication system?

The signal used in the HA-I pathway of vibrio harveyi is (Z)-3-aminoundec-2-en-4-one. it is an intragenus communication

What enzyme synthesises the signal?

Intraspecific communication

HA-I pathway: what kind of communication system? What kind of signal is used?
What enzyme synthesises the signal?

intraspecific communication

Uses AHL autoinducers

LuxM enzyme

AI-2 pathway

What kind of communication system? What enzyme synthesises the signal?

General communication

LuxS