Sensing and signal transduction

Question 1

What are two component regulators

Answer 1

• External signal detected by sensor (typically a kinase in inner cytoplasmic mebrane)
• Then response regulator within the cytoplasm.

Trans autophosphorylation of sensors (dimers)

• this occurs on Cytoplasmic histidine residues
• Gamma phosphoryl ATP molecule known as histidine kinase

Phosphate group transferred from kinase to aspartate residues on response regulator which then binds DNA to regulate transcription

Regulatory loop completed by the phosphatase that removes phosphate from RR, activity can be on RR itself or another protein.

Overall can involve many His-Asp phosphorylation steps and may allow for complex Regulation.

Question 2

Whats the distribution to Two Component Regulators (TCRs)

Answer 2

• Common in most bacteria
• Absent only in pathogens and endosymbionts with severely reduced genomes (e.g mycoplasma)
• Average 30 TCRs per genome
• Almost 50 in Ecoli
• > 200 in Myxococcus xanthus

Question 3

Give examples of TCR systems seen before.

Answer 3

• Bundling in flagella rotation (separate sensor is MCP, sensor less histidine kinase CheA and the response regulators are CheY/B)
• Sporulation activation
  its a Phosphorylation cascade which allows for complex regulation.
• Quorum sensing AL-2 as the signal molecule and its the LuxQ/LuxO system.
• VanS/VanR system for antibiotic resistance with the signal molecules Vancomycin
• EnvZ/OmpR for osmolarity
• PhoQ/PhoP for virulence with the signal molecule being Mg2+ and Cationic antimicrobial peptides (CAMPs)

Question 4

Example the VanS/VanR system

Answer 4

• Vancomycin is a glycopeptide antibiotic important for entercoccal infection post surgery and MRSA by binding D-ala-D-ala on terminus of lipid II causing no traspeptidase activity of DD-TPase so no crosslinking, no useful in gram negatives
• Expression of Van genes provides resistance and activated by VanS/VanR TCR
• Histidine residues are phosphorylated by ATP (autophosphorylation) on VanS histidine Kinase then phosphorylates phosphate residue on VanR which then regulates the DNA transcription (response regulator) to remodel to cell wall precursors to enable crosslinks resistance to vancomycin

Question 5

Explain Ecoli EnvZ/OmpR TCR system

Answer 5

• It responds to environmental osmotic changes
• EnvZ is a histidine Kinase which undergoes trans-autophosphorylation of His residues which in tern is transferred to Asp of OmpR the response regulator which is a transcription factor controlling regulation of ompC/OmpF

These genes form channels for passive diffusion

EnvZ is regulated by osmotic signals, but EnvZ posseses OmpR-P phosphatase to dephosphorylate OmpR-P

Question 6

Explain the Salmonella PhoQ/PhoP system

Answer 6

• involved in virulence of gram negative pathogens
• Mg2+ binds to Acidic residues on PhoQ (negative) then host defences try to displace mg2+ with cationic microbial peptides which are positive and cause conformational change causing phosphorylation from ATP to (histidine residues of histidine kinase) PhoQ which transfers to aspartate on PhoP causing it to change to PhoPP which regulates expression of phoP (activation) or pag (repressed) genes.