Chemotaxis Flashcards
Chemotaxis=
Allows microorganisms to grow and survive in diverse environments.
CCW rotation of flagella=
CW rotation= (different for peri vs mono)
CCW= movement forward
CD= peri–> tumbling
mono–> backwards
Three classes of proteins that are essential:
How many main proteins direction the direction of flagellar rotation? and How many sence atractant concentration?
1) transmembrane receptors
2) cytoplasmic signaling components
3) enzymes for methylation
4 proteins for directing the direction
2 for sensing attractant concentration
How many Che proteins?
and what they do?
6 cytoplasmic proteins called Che proteins, transduce information from the receptors to the motor.
name the 6 Che proteins and what they do?
CheA= kinase
CheY= response regulator
CheW= receptor-coupler
CheZ= dephosphorylation
CheR= methyltransferase
CheB= methylesterase
operons and what they consist of:
- Mocha –> Mot A, Mot B, CheA, and CheW
- Meche –> Tar, Tap, CheR, CheB, CheY, and CheZ
flagellar operons divided into how many classes?
class 1=
class 6=
divided into 6 classes
Class 1- (flbB controls all other operons)
Class 6- (hag operon ((flagellin)))
MCPs=
how many chemoreceptors are there and what do they sense?
MCPs= methyl-accepting chemotaxis proteins; membrane receptors which are homodimers that span the membrane.
There are five chemoreceptors: Trg, Tap, Tar, Tsr, and Aer
Five senses that each detect a different subset of attractants and repellants.
3 types of signalling
where does the sensory domain lie?
where does the signaling domain reside?
Signal reception
Signal transduction
Signal adaptation
Sensory domain lies in the periplasm
Signaling domain resides in the cytoplasm
modulating the level of CheY-PO4 does what?
modulate the level the freq of tumbling, walking, and swimming
How is CW rotation (tumbling) activated?
When transphosphorylated by CheA, CheY can interact with the FliM component of the motor and trigger CW rotation (tumbling)
Natural tendency of the flagellar motor is?
toward CCW rotation (smooth swimming)
Flagellar motors have?
“a clutch”
when engaged it swims, and when it is disengaged its stationary
attractants increasing does what?
repellants increasing does what?
tumbling decreases
tumbling increases
For walks and twiddles:
7 steps
1) when a receptor is free
2) autophosphorylation of CheA
3) PO4 transfer from CheA-P to CheY
4) CheY-P binds to motor and causes a CW rotation
5) CheZ dephosphorylates to maintain a level of phosphorylation (CheY-P)
6) CheZ protein is a CheY phosphatase that lowers the level of CheY-PO4
7) Non-phosphorylated CheY doesnt affect the motor switch, thus it supresses tumble frequency and increases the length of smooth swimming.
When a receptor meets an attractant:
- a conformational change occurs to the sensory domain of MCPs and subsequent changes to autophosphorylation of CheA occurs
- Repellans (negative effectors) = increase in CheA autophosphorylation.
CheR vs. CheB
- Che R (add) and CheB (remove)
- CheB can also increase net neg. charge
- CheB part of feedback loop
- CheB “competes” with CheY for CheA-PO4
- CheB-PO4 activates methylesterase activity (removal)
- Increased kinase activity follows…but,
- CheB continues to remove methyl groups, and as a result, negative charges intensify, MCPs repel each other, CheA-PO4 levels decrease, leading to smooth swimming.
chemotactic memory=
methylation of membrane receptor signal domain following excitation (MCPs)
1) transphosphorylated by CheA=
2) goal is to=
3) as a result, CheA autophosphorylation=
4) Nonphosphorylated CheY…
1) When transphosphorylated by CheA, CheY interacts with FliM (motor) and triggers CW rotation (tumbling).
2) Goal is to modulate tumble frequency.
3) As a result, CheA autophosphorylation and transphosphorylation of CheY stop.
4) Nonphosphorylated CheY does not affect the motor switch, and thus, suppresses tumble frequency and increases the length of smooth swimming.
Low CheY-P=
High CheY-P=
swimming (CCW)
tumbling (CW)
what domain does CheY bind to of CheA?
What does this change cause?
and directly interacts how?
CheY binds to the YB domain of CheA, phosphate group transferred to CheY
CheY-P causes conformational change in CheA that decreases its affinity for P but increases affiniy for FliM for P
CheY directly interacts with the flagellar switch motor and induces swimming, modulation of direction and/or speed
how do cells sense attractant concentration? repellant?
2) happens by?
3) steady state?
attractant= increase in CH3
repellant= decrease in CH3
2) methytransferase CheR and methyesterase CheB
3) steady state: CheR adds CH3 to MCPs to balance their removal by CheB-P
Proteins involved in adding and removing CH3 on the MCP groups:
Methyltransferase CheR methylates glutamate residues
Methylesterase CheB removes methyl groups; as well as “resets” the receptor for excitation…
1) methylation of MCP’s does what?
2) Low concentration or when repellant is bound=
3) under these conditions?
4) in this state MCPs have?
1) monitor attractant concentration
2) most of the MCPs are in the CW state
3) CheA is activated, and CheB removes most of the methyl groups
4) MCPs have high affinities for the attractants and are able to detect very low concentrations of these effectors.
How does the cell know it should continue to move toward higher concentrations of attractant?
- adaptation and desensitization
- chemotactic “memory” involves the methylation of the membrane receptor signal domain following “excitation”
- methyl-accepting chemotaxis proteins
1) CheA complexes with?
2) CheA autophosphorylates and transfers P to?
3) CheY-p binds to?
4) Attractants suppress?
5) Repellants induce?
6) Adaptation is carried out by?
1) CheW
2) P to CheY
3) motor causing (CW-tumbling)
4) autophosphorylation
5) autophosphorylation
6) carried out by CheR and CheB (methylation), PMF, and Mot A&B.
1) Proton motive gradient controlled by?
2) “strokes”
3) PMF and recall happens?
4) Flagellar movement is?
1) Mot A and Mot B
2) Strokes to move the rotor by hydrogen protons entering the proteins, attaching to aspartic acid residues causing a conformational change of the proteins.
3) PMF, recall, happens at the CM (ATPase, ETS, and chemiosmosis)
4) ATP expensive!
