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Molecular Microbiology > Lecture 6: pili & flagella > Flashcards

Lecture 6: pili & flagella Flashcards

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Biology 101 flashcards
1
Q

Movement of bacteria: examples?

A
  1. Swarming
  2. Swimming
  3. Twitching
  4. Gliding
  5. Sliding
  6. Brownian motion (not active motility)
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2
Q

Bacterial flagellum: general remarks?

A
  • Composed of lots of proteins (ten thousands)
  • Turning of motor at expense of high amount of protons
  • Lots of energy used
  • speed = 30 bodylengths/s
  • can switch direction without changes in rotation speed
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3
Q

Bacterial flagellum: secretion machinery homologous to?

A

type III secretion

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4
Q

Not all bacteria have flagella, highly conserved between different species

A

ok

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5
Q

D1 domain is very conserved and characteristic of flagella. Recognized by?

A

innate immune system of host (TLR5)

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6
Q

What is generally the most important signal for flagellum biosynthesis?

A
  • Rise in cAMP
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7
Q

Master regulator FlhDC controls?

A

the production of basal body and hook proteins

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8
Q

When is the basal body finished? What is the length?

A

as soon as the cap penetrates the outer membrane. Length = entire periplasm

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9
Q

Width of basal body is determined by?

A

determined by Braun’s lipoprotein (LPP)

Protein is made longer/shorter: basal body is also longer/shorter

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10
Q

FliK determines hook length. How is that done?

A
  • FliK: secreted through flagellum, interacts with hook cap (FlgD)
     Upon reaching the correct length, FliK can now interact simultaneously with FlgD at one end and FlhB at the other end
     FliK Induces auto-proteolytic cleavage of FlhB
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11
Q

What happens when FlhB is cleaved by FliK?

A

• FlhB is a the centre of the flagellar secretion machinery and determines specificity -> cleavage of FhlB changes specificity !

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12
Q

FlgM = anti-sigma factor. What happens when FlgM is secreted?

A

If the basal body is completely finished, FlgM is also secreted, blocker is gone, sigma factor released, filament proteins can be made

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13
Q

Length of bacterial flagellum: how is it determined?

A

Length is determined by how well the subunits can still move to the end of the flagellum and be incorporated. Diffusion of subunits determines flagellar growth.

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14
Q

What does the flagellum stator do? Examples of stators? Energized by atp?

A

Stabilizing & energizing the system: they are the rotating unit. NOT ATP

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15
Q

What results in variable speed of rotation of flagellum?

A

Number of stators is variable, resulting in variable speed.

Type of stator can be changed during rotation.

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16
Q

What stator complex is mostly used? What other complex is therE?

A

MotAB stator. For H+ uptake.

Also: PomA stator for when there is lots of sodium irons around (Na+)

17
Q

Most important part of contact with the stator?

A

with the FliG part of the ‘big ring’ in the cytosol.

18
Q

When the stators (motABs: outside) spin in clockwise fashion, the flagellum spins in..

A

a counter-clockwise fashion (inside: located at the inner ring of all MotABs)

19
Q

How to let the flagellum move in the other direction?

A

Inner ring of MotABs (blue: flagellum) can expand and then it can contact the other side of the stators. Spinning speed will therefore always stay the same, as the MotABs will always spin in the same direction.

20
Q

Bacterial swimming: monotrichous
Forward movement =
Reverse movement =
(direction of spinning)

A

Forward: CCW
Reverse: CW

21
Q

Bacterial swimming: Petrichous
CCW = ?
CW = ?

A

CCW = bundling of the flagella (like one super flagella) and a forward movement

CW = flagella bundle dissolving and ‘tumbling’

22
Q

What is chemotaxis and how is it achieved?

A

Chemotaxis = movement towards or away from stimulus. Achieved by modifying CCW vs CW ratio.

23
Q

How is Swarming on solid surfaces achieved? What can swarming result in?

A

dependent on flagella and surfactant.
Team up and secreting surfactant for swarming movement.
Can result in different terraces on agar plates.

24
Q

What is the function of pili?

A

 Adhesion to host cells
(cells do not easily associate due to electrostatic repulsion)
 Adhesion other bacteria (biofilm)
 Uptake DNA (transformation)
 Transfer DNA (conjugation)
 Movement: Twitching motility (bacteria) and archaellum (Archea)
 Biological nanowires (Geobacter sp.)

25
Q

Flagella vs pili ?

A

 Flagella are produced at the top (substrates secreted unfolded through hollow centre), Pili mostly growing from the base (exception: curli – type III)
 Flagella are hollow, Pili mostly not (except for some pili produced by type III and type IV secretion)
 All bacteria (NOT Archae!) have a similar flagellar machinery, whereas there are different types of pili

26
Q

What is the Chaperone-usher pathway?

A
  • > to make a pilus
  • Assembly regulated by two proteins, a periplasmic chaperone and an usher in the OM
  • OM assembly INDEPENDENT of energy source (ATP, proton gradient)
27
Q

What are the first steps in the chaperone-usher pathway?

Step 1. transport across inner membrane and periplasm?

A

 Sec-mediated IM transport
 Cleavage of signal sequence
 Binding to periplasmic chaperone
Pili subunits have an incomplete immunoglobulin fold
 Immunoglobulin fold is a two layer sandwich of 7 β-sheets, with hydrophobic domains pointing inwards

28
Q

What happens with the incomplete immunoglobulin fold when binding to a chaperone?

A

Donor strand complementation: Incomplete immunoglobulin fold of pili subunits is complemented by β-strand of the chaperone.

29
Q

Why is the donor strand complementation of the immunoglobulin fold of pili subunit not 100% complete?

A

Because

  1. donor strand of chaperone does NOT completely fill the hydrophobic cavity of the immunoglobulin fold (P5)
  2. Donor strand NOT antiparallel
30
Q

How are subunits pasted together after binding to chaperone?

A

Zip-in Zip-out mechanism using the empty P5 spot. Also donor strand exchange, but now with N-terminal extension of the other subunit, and this time complementation is antiparallel.

When bound to chaperone, another subunit can bind to the P5 unit as it is empty. Then, it can start pushing out the chaperone and replacing it.

31
Q

What does the usher look like? Role of usher protein?

A
  • The usher is a 24 stranded β-barrel with a central plug domain
  • In addition, the usher has a large N- and C-terminal periplasmic domain
  • This plug is removed when the pilus is produced
  • Helps in making pilus
32
Q

Usher-chaperone model?

A
  1. Protein + chaperone can bind to NTD domain (or CTD). Starts to interact with other protein
  2. Donor strand complementation
  3. Chaperone falls out, subunits bind
  4. New protein comes in, starts to interact etc
33
Q

What determines order of subunit insertion?

A

Tip subunit (bound to chaperone) has highest affinity for usher
Nature of P5 hole and number of subunits determine order
 terminal subunit has no P5 cavity. Can therefore not be extended.

Molecular Microbiology (12 decks)

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