Microm 410 Fall 2009: Chemotaxis Dr....

Microm 410 Fall 2009: ChemotaxisDr. Lara

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• Phototaxis: movement in response to certain wavelengths of light.

• Aerotaxis: movement in response to 02 or a gradient of 02.

• Thermotaxis: Response to temperature or a temperature gradient.

• pH taxis: Movement towards/away from acid/alkaline environments orgradients.

• Magnetotaxis: The directed movement along geomagnetic lines offorce.

• Chemotaxis: biased movement in response to certain chemicalsknown as CHEMOEFFECTORS (attractants or repellents). Not allchemicals are chemoeffectors nor are all chemicals that are “nutritious”attractants!

Bacterial Tactic Responses A common theme that runs through manyprokaryotic sensory and regulatory mechanisms is(1) the use of allosteric proteins, proteins whoseproperties change when associated, in a non-covalent fashion, with a low molecular weightmolecule, called an EFFECTOR MOLECULE OR ALIGAND, and/or (2) reversible covalent modificationof certain proteins (methylation or phosphorylation).

In absence of a chemoeffector movement is random

Swimming

Absence of a chemoeffector

Tumbling

1-2 sec: 20 µ/sec or 10-20 bodylenghts/sec

0.1 sec

+ attractant

adaption

-attractant

de-adaption

Behavioral Response toan Attractant

timeline

Chemotaxis is a transient phenomenon

Chemotaxis has a:-Transient component-Temporal component

Chemotaxis is the result of regulation offlagellar rotation

What accounts for the swimming/tumbling motion?

Swimming is the result of counter clockwise rotation of flagellum

Tumbling is the result of clockwise rotation of flagellum


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• Stimulus (i.e., chemoeffector molecule).

• System to detect chemoeffector (chemoreceptor).

• System to process signal (which must include a way tomeasure and compare present with the past environment).

• Production of an appropriate output response; either a CW(cell tumbles) or CCW (cell swims) rotation of theflagellum(a).

Components of a SensorySystem Chemoreceptors

• periplasmic binding protein

• Methyl accepting membrane proteins (MCP’s)

• enzyme IIc of the PTS

-Maltose binding protein (MalE)- two functional domains

+ A (-R) methylation goes up+ R (-A) methylation goes down

Four Classes of MCP's:

• MCP 1 (Tsr gene product)- serine plus certain repellents (weakacids/indole/leucine); 2000 copies/cell, 6 methylationsites/molecule.

• MCP II (Tar gene product)- maltose/aspartate, repellents Co+2

and Ni+2, ~1000 copies/cell, 4 methylation sites/molecule.

• MCP III (Trg gene encoded)- ribose/galactose, 100-200copies/cell, ~5 methylation sites/molecule.

• Tap gene- In E. coli used to detect dipeptides.

Each of these proteins will have an inherent level ofmethylation in the absence of any chemoeffector.

Methly Accepting Proteins (Transducer Proteins)

The amount of chemoeffector-binding proteinassociated with MCP II is a measure of the cellspresent environment, and the level of methylationof MCP II is a measure of the cells pastenvironment.

Chemotaxis is a dynamic process


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• CheR- Methyl transferase, methylates exposed glutamyl residues ofMCP's (enzyme is "slow" acting meaning it takes longer to addmethyl groups than to remove same number of methyl groups).

• CheB- Methyl esterase, removes methyl groups from glutamylresidues ("fast" acting).

• CheA- An autophosphorylating protein kinase. Protein canphosphorylate itself and then transfer phosphate group to CheY andCheB.

• CheY- when phosphorylated can bind to a switch protein, FliM, andbiases rotation of flagellum in the clockwise direction (causes cell totumble).

• CheZ- Controls level of phosphorylation of CheY(dephoshorylation).

• CheW- link between MCP and CheA.

Methyl donor: SAM, S-adenosyl methionine

Enzymes/Proteins Involved in Chemotaxis:

Chemoeffector (maltose)

LamB (porin)

Maltosebinding protein

MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace

CH3Maltosetransporter

Chemotaxis Model


LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



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LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



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LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



LamB (porin)


MCP II

ocwm

Cytoplasmicmembrane

Periplasmicspace



LamB (porin)


ocwm

Cytoplasmicmembrane

Periplasmicspace

CH3Maltosetransporter Glutamyl

CheW SIGNAL PROCESSED

Decrease frequency of tumbling (TurnFlagellum CCW for longer periods)


LamB (porin)


ocwm

Cytoplasmicmembrane

Periplasmicspace

CH3Maltosetransporter Glutamyl

SAMCheR


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LamB (porin)


ocwm

Cytoplasmicmembrane

Periplasmicspace

Maltosetransporter

Glutamyl-CH3CH3

Adaptioncomplete


LamB (porin)ocwm

Cytoplasmicmembrane

Periplasmicspace

Maltosetransporter


CH3 CH3CH3 CH3

Phospho-CheB


LamB (porin)ocwm

Cytoplasmicmembrane

Periplasmicspace

Maltosetransporter


CH3CH3 CH3

De-adaption


LamB (porin)ocwm

Cytoplasmicmembrane

Periplasmicspace

Maltosetransporter


CH3CH3 CH3

CheW

SIGNAL PROCESSED Flagellum returns tonormal frequency ofCW/CCW


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Signal Processing

CheW

CheA phospho-CheA

ATP ADP

CheY

phospho-CheY

CheB (inactive)

phospho-CheB(active)

Binds to FliM,CW rotation offlagellum

+repellent

CheZ

+ attractant X

Removes methyl groupsfrom MCP’sCCW

phospho-CheY

CW rotationCCW rotation

Chemoreceptors

• periplasmic binding protein

• Methyl accepting membraneproteins (MCP’s)

• enzyme II of the PTS

-no methylation involved-transport required to elicit chemotatic response-unphosphorylated form of enzyme 1 of PTSsystem inhibits autophosphorylation of CheA

Microm 410 Fall 2009: Chemotaxis Dr....

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