Lecture 4. Motility and Chemotaxis in Bacteria Flashcards
How do bacteria move ?
Use flagella and a proton motor force
What is a proton motor force ?
Protons move from a high-density area on the periplasm side of the inner membrane along a proton motor gradient through the motor, causing the motor to turn
What happens when flagella rotate anticlockwise ?
The flagella bundle forward at a great speed
What is a run ?
When flagella rotate anticlockwise causing the flagella to move forward at a great speed
What happens when the flagella rotate clockwise ?
The flagella bundle unravels and the bacteria tumbles
In a homogenous environment, is there an equal number of run and tumbles ?
Yes
What is a random walk ?
An equal amount of run and tumbles, in a homogenous environment
What happens to run and tumbles, when the environment is improving over time ?
There are more runs than tumbles
What does the motor filament structure require in flagella motor filament ?
Many genes
What does the expression of many genes in the motor filament structure form ?
Protein monomers
What is an example of protein monomers ?
FliC
What causes the motor to turn ?
Protons moving along a protein gradient from the periplasmic space moving between the stator and motor before moving into the cytoplasm
What is the motor filament export apparatus known as ?
A type 3 secretion system
What is the order of assembly in flagella ?
- Motor
- Hook
- Filament
What does the export apparatus do ?
Moves protein monomers through the centre of the assembled structure until they reach their destination where they self assemble
What are transcription genes involved in the motors filaments structure function ?
They are tightly regulated in the timing of their activation
What are the master regulators involved in flagellum expression ?
flhC and flhD
Where are flhC and flhD expressed from ?
The flhDC operon
What is the flhDC operon linked to ?
Many stress responses of cells
What is the flhDC operon positively enhanced by ?
The cAMP-CRP activation complex
What does the cAMP-CRP activation complex create ?
A transcriptional activation complex that activates the middle genes
What do sigma factors form in flagellum gene expression ?
Components of the RNA polymerase complex that direct complexes towards specific classes of promoters
What is the sigma factor responsible for directing the polymerase complex towards the later genes ?
FliA/sigma 28
When the middle genes are being expressed what is FliA bound to and inactivated by ?
FLGM
What is FLGM ?
An anti-sigma factor
What happens once middle genes are finished doing their jobs ?
The FLGM protein detaches from fliA and moves through the flagella complex. FliA can now direct RNA polymerase towards the late genes/spatial temporal regulation
How are the flagella of E.coli arranged ?
Peritrichously - spread over the entire surface
What helps salmonella to evade host defences ?
FliC being replaced by FliB - randomly switching
What is the name for the process of salmonella evading host defences ?
Phase variation
In the genetic of flagellin protein expression in salmonella, what does bacteria randomly switch between ?
Either flijBA operon or fliC gene
In the genetic of flagellin protein expression in salmonella, is the switching random ?
No it is biased towards switching from phase H2 to H1
In the genetic of flagellin protein expression in salmonella, what happens in phase H2 ?
The flijBA operon and the fliC gene is off
In the genetic of flagellin protein expression in salmonella, what happens in phase H1 ?
The fljBA operon is off and the fliC gene is on
What is fljA ?
An inhibitor of fliC expression that acts post transcriptionally and blocks the translation of fliC mRNA
What is the fljB fljA operon ?
Invertible
Where is DNA in the chromosome physically inverted ?
Between the hixL and hixR inverted repeats
What is an inverted repeat ?
A single stranded sequence of nucleotides followed downstream by its reverse complement
What is H switch ?
The invertible genetic element of DNA in the chromosome
What are hixR and hixL ?
Identical but orientated in opposite directions
When are genes no longer transcribe in the genetic of flagellin protein expression in salmonella ?
Once the promoter faces away from the operative genes
What encodes Hin invertase ?
9966-bp H-switch
What is Hin invertase?
A site specific recombination protein – serines recombinase
Where are hin repeats bought together ?
At an enhancer region within the Hin gene
What are Hin repeats held in place by ?
The Hin protein tetramer
What cuts DNA at inverted repeats ?
Catalytic components of invertors
How is the Hin invertasome formed ?
DNA swap positions with respect to the rest of the genome and re-join ends - inverting the switch
What are HU and FIS ?
Architectural DNA binding proteins and are also known as KNAPs
What does KNAP stand for ?
nucleate associative proteins
What is the role of KNAP In the genetic of flagellin protein expression in salmonella ?
Structure DNA in the nuclear site in a highly organised fashion
What does protein HU help ?
Loop formation and helps tight bending in the smaller loop
What does protein FIS do ?
Enhances Hin activity by stabilising correct DNA topology
Why is the right loop larger ?
As it is not equidistant from the inverted repeats
Why can the right loop form on its own ?
Due to the intrinsic ability of DNA to bend
What is chemotaxis ?
A system that detects signals from the environment, transduces signal across the membrane into the cell and causes an effect which allows bacteria to respond to the situation
How does chemotaxis occur ?
Using signal transduction by a two component regulatory system
What does the sensor protein have ?
A transmitter component containing a histidine residue
What does the output protein contain ?
A receiver domain with a conserved aspartic acid
What happens when a sensor receives a signal ?
The structure changes slightly and causes the histidine residue in the transmitter domain to become phosphorylated
What happens after the transmitter domain becomes phosphorylated ?
It in turns phosphorylates the receiver domain of the output protein on the conserved aspartic acid residue
Where is the sensor histidine kinase ?
Embedded in the cell membrane
What is the methyl accepting chemotactic protein ?
The sensor histidine kinase embedded in the cell membrane
What happens when the MCP detects the signal from outside the cell ?
It initiates the signal cascade by becoming phosphorylated on the histidine.
This in turn causes the phosphorylation of the aspartic acid in the output side of the system
What is a methyl accepting protein monomer composed of ?
Up, down up down four helical structure
What do the first and last helixes of the methyl accepting protein extend into ?
The cytoplasm
What does the sensing domain homodimer of the methyl accepting protein have ?
Two symmetrical, non - overlapping aspartate binding sites at the dimer interface
What does binding at the aspartate at either symmetric site act as ?
A confirmation change that precludes binding to a second site
What is an example of further ligand induced conformational changes which is the source of signaling across the cell membrane or inhibitor of cheA kinase activity in the cytoplasm ?
The downwards piston like movement of the second transmembrane helix, with the first transmembrane helix and a rotation of the dimer subunits
What creates a short term memory within the chemotaxis system allowing it to constantly reset ?
Cycles of methylation by cheR and cheD by cheBs by MCPs
What happens in methyl accepting protein monomer when attractants are present ?
The alpha helical bundles remain apart and cheA remains inactive
What happens when methyl accepting protein attractants are absent ?
The bundles come together and cheA becomes phosphorylated with the help of cheW
What happens when cheA is active and phosphorylated ?
It fuses to the motor complex where it in turn is phopshorylated by cheY
What does phosphorylated cheY do ?
It interacts with film motor proteins and causes tumbling to be suppressed
What does cheY become dephosphorylated by ?
CheZ and the system is reset
What are the chemoreceptor sensory domains of methyl accepting protein linked by ?
Conserved cytoplasmic domains
