Scenario 4

1
Scenario 4
Listeria move inside host cells by recruiting
actin
2
Scenario 4

• Listeria
• Human pathogen L. monocytogenes (rod shaped)
• Risk of infection from unpasteurized dairy
  products
• Particularly dangerous in pregnancy
• Grows at 30C, ie. in refrigerators

3
Scenario 4

• Listeria
• Invades cells of host tissue, thus evading
  immune response
• Moves inside and between cells by recruiting a
  rocket-like tail of host actin

4
Scenario 4

• Listeria
• Human pathogen L. monocytogenes (rod shaped)
• Risk of infection from unpasteurized dairy
  products
• Particularly dangerous in pregnancy
• Grows at 30C, ie. in refrigerators
• Invades cells of host tissue, thus evading
  immune response
• Moves inside and between cells by recruiting a
  rocket-like tail of host actin

5
Scenario 4

• Crawling/gliding locomotion of animal tissue
  cells
• Important component of mechanism is protrusion
  of front. Typically a thin fan-like structure,
  known as lamellipodium, or leading lamella.
• Nerve growth cone is similar
• Now good evidence that Is driven by
  polymerization of actin filaments at the front
• Key molecular components of this mechanism are
  recruited by Listeria

6
Scenario 4

• Conservation of actin sequence
• is usually attributed to extremely large number
  of proteins (100) which interact with it.
• Among their functions
• Binding (sequestration) of G-actin monomers
• Self assembly
• Nucleation of filament assembly
• Scission of filaments
• Cross-linking of filaments
• And many others

7
Scenario 4
Protomer of actin filaments is known as
G-actin Molecular weight 43 kDa 4
sub-domains ATP-binding cleft
8
Scenario 4

• Polymerization of actin in vitro
• Actin typically isolated from skeletal muscle
• Globular/Filamentous (G/F) transition
• Controlled by ionic conditions
• Water (mM ATP mM Mg2 solubilises G-actin
  monomers. (Low salt promotes electrostatic
  repulsion)
• 0.1 M NaCl (as inside cells) drives assembly

9
Scenario 4

• Prokaryote ancestry of actin
• Bacterial protein MreB forms large fibrous
  spirals underlying membrane of rod-shaped cells.
  Has role in determining cell shape.
• Mre is abbreviation for murein cluster e.
  (Murein is the bacterial cell wall
  peptidoglycan).
• MreB has 3D structure extremely similar to
  G-actin, although overall sequence identity is
  only 15.
• MreB forms filaments very similar to single
  actin protofilament

10
Scenario 4
Green squares Hydrophobic loop which moves to
stabilise twin protofilaments Catch 22!
11
Scenario 4

• Arp2 3 complex a signal-regulated device for
  initiating
• actin polymerisation
• Complex of seven subunits including
  Actin-related proteins Arp2 and Arp3. Conserved
  from yeast to man.

12
Scenario 4
Arp Actin-Related Protein Arp 2 3 complex, with
5 other proteins
13
Scenario 4

• Arp2 3 complex a signal-regulated device for
  initiating
• actin polymerisation
• Complex of seven subunits including
  Actin-related proteins Arp2 and Arp3. Conserved
  from yeast to man.
• Is activated at surface of Listeria by the ActA
  protein
• stimulating actin polymerization and bacterial
  propulsion

14
Scenario 4
Listeria recruits host cell Arp2-3 complex via
single bacterial protein (Act A) and generates
own propulsive actin tail
15
Scenario 4

• Arp2 3 complex a signal-regulated device for
  initiating
• actin polymerisation
• Complex of seven subunits including
  Actin-related proteins Arp2 and Arp3. Conserved
  from yeast to man.
• Is activated at surface of Listeria by the Act A
  protein
• stimulating actin polymerization and bacterial
  propulsion
• Activation may place arp2 and arp3 in spatial
  relation as if
• actin monomers in the actin filament

16
Scenario 4

• Arp2 3 complex a signal-regulated device for
  initiating
• actin polymerisation
• Localises at motile regions of animal cells
• Generates new actin filaments in response to
  signals, by starting new branches (dendritic
  polymerization)

17
Scenario 4

• Arp2 3 complex a signal-regulated device for
  initiating
• actin polymerisation
• Activation may place arp2 and arp3 in spatial
  relation as if actin monomers in the actin
  filament
• Activation by Listeria requires just Act A
  protein.
• Activation in mammalian cells by signalling
  protein which joins the arp2-3 complex. E.g WASP
• WASP Wiskott-Aldrich Syndrome Protein.
  Syndrome is X-linked recessive defect in
  leucocyte chemotaxis.

18
Scenario 4
Listeria move inside host cells by recruiting
actin