VL6: Two component systems Flashcards
What are the take home messages?
- TCS are very widely used regulators
- They are used to regulate behaviour and/or gene expression
- They detect the environment and transmit a signal onwards
What are TCS?
- Sensor (Kinase), senses the environment
phosphorylation of second component when sensor is stimulated - Response Regulator mediates a response
phophrylated form of second componend is the active state of the regulator
What components/domains are TCS made up of?
Histidine Kinase:
- Sensing domain (N-terminal)
- Dimerization domain (carries phosphate, that gets passed on)
- ATP binding kinase domain (Transmitter=autokinase)
Response regulator:
- Regulatory domain (gets phosporylated)
- Effector domain
What 2 groups of kinases exist?
- Membrane associated proteins sense envrionmental signal
- Cytoplasmic proteins are usually part of a pathway that is more complex than a simploe TC mechanism and they respond to intracellular signals
What is chemotaxis and how does it work?
Straight run followed by tumble (to randomize direction), random walk up or down a concentration gradient
attractant or repellents cause a biased random walk
they swim and taste environment and decide if it getting better or worse
How does chemotaxis work on a molecular level?
Attractants are caught by transducer (MCP= methyl accepting chemotacis proteins)
if bound, CheA (=sensor kinase) autophosphorylates
CheY (=response regulator) controls flagellar rotation
CheZ-dephosphorylates CheY-P
CheB also response regulator, regulates methylation level of MCP
What are flagella?
Flagella are long whiplike filaments composed of protein that originate in the cell membrane
Flagella rotate and impart swimming movement on the cells
Name/Explain 4 types of flagella
- Monotrichous: a single flagellum usually at one pole (vibrio cholerae)
- Amphitrichous: a single flagellum at both ends of the organism
- Lophotrichous: two or more flagella at one or both poles
- Peritrichous: flagella over entire surface
What is the opportunity cost of flagella?
flagella synthesis is expensive and requires up to 30 genes and about 10 more genes encoding proteins for hook and basal body
How do flagella move?
rotation of the filament is driven by diffusion of protons into the cell through the basal apparatus after the protons have been actively transported by proton pumps in the plasma membrane
filament is rotated by a protein motor in the cell membrane
motor is powered by proton motive force (pmf)
What parts do flagella consist of?
- basal body (series of rings that drive the flagella)
- hook (short curved segment that links flagellin to the basal body
- Flagellin (hollow rigid cylinder constructed of a single protein (Filament)
How do chemoreceptors influence flagella movement?
The methyl-accepting chemotaxis protein (MCPs) form clusters associated with the CheA and CheW proteins
lots of different receptors for different signals (serine, aspartate, dipeptides sugars ect)
How is chemotaxis influenced by signal transduction?
-small molecules diffuse through pores of OM, bind to protein receptors in cell membrane, binding of atttractant reduces the rate of phosphorylation and thus prolongsthe runs (less tumbling)
methylatioon resets the cells sensitivity to the attractant, sot it requires a higher concentraion of attractant next time to reduce phosphorylation and prolong the run thus the bacteria can sense a concentration gradient by measuring a difference between what it was before and what it is now
–> attractant binding reduces tumbling frequency and drives swimming
Signal transduction step by step
- if no attractant is bound to MCP
- CheW stimulates autophosphorylation (cheA -> CheA-P)
- CheA-P transfers P to CheY (making CheY-P)
- CheY-P interacts with flagella motor protein ->tumbling
- CheZ de-phosphorylates CheY-P (making Che-Y)
- CheZ activity ensures bacteria can go from trumble ->Run
- CheA-P also transfers P to CheB (making CheB-P)
8: CheB-P de-methylates MCP receptor protein - Unmethylated MCP is more sensitive (binds ligand)
- MCP with bound ligand slows the CheA autophosphorylation
- Low rate of CheY phosphorylation
- Low rate of interaction with flagella motor
- Flagella mortor moves CCW (bacteria runs)
- If the concentration of ligand is high the run is long
- CheR continuously methylates the MCP
- Methylated MCP is less sensitive to ligand
- Methylated MCP stimulates CheA->CheA-P autophosphorylation
- Methylated MCP stimulates tumbling
- CheR and CHeB activity ensure system can adeapt to new concentrations
- CheZ ensures the system does not get stuch in on mode
what is RpoS?
=Sigma S (sigmayeichen)S
- sigma factor induced in response to stress like lack of nutrients
- re-directs RNA polymerase transcription activity
- regulated via TCS
