Chemotaxis

Question 1

Chemotaxis=

Answer 1

Allows microorganisms to grow and survive in diverse environments.

Question 2

CCW rotation of flagella=

CW rotation= (different for peri vs mono)

Answer 2

CCW= movement forward

CD= peri–> tumbling

mono–> backwards

Question 3

Three classes of proteins that are essential:

How many main proteins direction the direction of flagellar rotation? and How many sence atractant concentration?

Answer 3

1) transmembrane receptors
2) cytoplasmic signaling components
3) enzymes for methylation

4 proteins for directing the direction

2 for sensing attractant concentration

Question 4

How many Che proteins?

and what they do?

Answer 4

6 cytoplasmic proteins called Che proteins, transduce information from the receptors to the motor.

Question 5

name the 6 Che proteins and what they do?

Answer 5

CheA= kinase

CheY= response regulator

CheW= receptor-coupler

CheZ= dephosphorylation

CheR= methyltransferase

CheB= methylesterase

Question 6

operons and what they consist of:

Answer 6

• Mocha –> Mot A, Mot B, CheA, and CheW
• Meche –> Tar, Tap, CheR, CheB, CheY, and CheZ

Question 7

flagellar operons divided into how many classes?

class 1=

class 6=

Answer 7

divided into 6 classes

Class 1- (flbB controls all other operons)

Class 6- (hag operon ((flagellin)))

Question 8

MCPs=

how many chemoreceptors are there and what do they sense?

Answer 8

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.

Question 9

3 types of signalling

where does the sensory domain lie?

where does the signaling domain reside?

Answer 9

Signal reception

Signal transduction

Signal adaptation

Sensory domain lies in the periplasm

Signaling domain resides in the cytoplasm

Question 10

modulating the level of CheY-PO4 does what?

Answer 10

modulate the level the freq of tumbling, walking, and swimming

Question 11

How is CW rotation (tumbling) activated?

Answer 11

When transphosphorylated by CheA, CheY can interact with the FliM component of the motor and trigger CW rotation (tumbling)

Question 12

Natural tendency of the flagellar motor is?

Answer 12

toward CCW rotation (smooth swimming)

Question 13

Flagellar motors have?

Answer 13

“a clutch”

when engaged it swims, and when it is disengaged its stationary

Question 14

attractants increasing does what?

repellants increasing does what?

Answer 14

tumbling decreases

tumbling increases

Question 15

For walks and twiddles:

7 steps

Answer 15

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.

Question 16

When a receptor meets an attractant:

Answer 16

• 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.

Question 17

CheR vs. CheB

Answer 17

• 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.

Question 18

chemotactic memory=

Answer 18

methylation of membrane receptor signal domain following excitation (MCPs)

Question 19

1) transphosphorylated by CheA=
2) goal is to=
3) as a result, CheA autophosphorylation=
4) Nonphosphorylated CheY…

Answer 19

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.

Question 20

Low CheY-P=

High CheY-P=

Answer 20

swimming (CCW)

tumbling (CW)

Question 21

what domain does CheY bind to of CheA?

What does this change cause?

and directly interacts how?

Answer 21

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

Question 22

how do cells sense attractant concentration? repellant?

2) happens by?
3) steady state?

Answer 22

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

Question 23

Proteins involved in adding and removing CH3 on the MCP groups:

Answer 23

Methyltransferase CheR methylates glutamate residues

Methylesterase CheB removes methyl groups; as well as “resets” the receptor for excitation…

Question 24

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?

Answer 24

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.

Question 25

How does the cell know it should continue to move toward higher concentrations of attractant?

Answer 25

• adaptation and desensitization
• chemotactic “memory” involves the methylation of the membrane receptor signal domain following “excitation”
• methyl-accepting chemotaxis proteins

Question 26

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?

Answer 26

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.

Question 27

1) Proton motive gradient controlled by?
2) “strokes”
3) PMF and recall happens?
4) Flagellar movement is?

Answer 27

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!