parasite motility and host cell invasion

Question 1

parasite motility strategies

Answer 1

• gliding (apicomplexa)
• flagellum based (kinetoplastidae)
• amoeboid (amoeba)
• variants on these (e.g. giardia)

Question 2

reynolds number

Answer 2

• dimensionless ratio of influence of inertial and viscous forces
• inertial = result of movement
• viscous = opposing movement (from the environment)
• Re>1 - inertial forces dominate
  
  • large objects have large Re - keep moving
• Re<1 - viscous forces dominate
  
  • small objects have small Re - stopped by viscous forces
  • stop propulsion e.g. flagella movement, cell movement stops

Question 3

reynolds number equation

Answer 3

Re = ρvL/η

ρ = fluid density and η = fluid viscosity (constants in aqueous environment)

v = velocity and L = size (variables)

Question 4

scallop theorem

Answer 4

• scallop (large Re) repeatedly opens and closes shell → propulsion
• moves because inertia dominates
• low Re microorganism is dominated by viscous
  
  • moves forwards and backwards as shell opens and closes
• microorganisms avoid repetitive movements
  
  • change shape or use continuous movement
  • e.g. flagella spiral like corkscrew

Question 5

crawling (amoeboid)

Answer 5

• wide use by eukaryotic cells too e.g. immune cells
• entamoeba histolytica
• lamellopodium-based
• actin and myosin push plasma membrane forward by polymerisation
  
  • form branch networks
• plasma membrane adhesion to surface with focal contacts (integrin)
• combined with contraction of rear end of cell

Question 6

swimming (flagellum based)

Answer 6

• type 1 flagella
  
  • bacterial secretion system derived ion pumps with rotating axis
• eukaryotic flagella
  
  • microtubule absed
  • ring of microtubules with central radial spoke
  • dynein motors walk up and down microtubules linking inner and outer cores
  • anchored microtubules slide against each other → bending
  • cycles of bending and releasing → whip-like motion

Question 7

T. brucei motility

Answer 7

• flagellum at one end extends along back
• moves flagellum-first
• combines with changing of protein coat

Question 8

gliding

Answer 8

• relies on unique cell organisation
• IMC houses sub-pellicular microtubule responsible for movement
  
  • 20nm wide
• motility intrinsic to invasion

Question 9

apicomplexan motility model

Answer 9

• secretory organelles release TRAP proteins to substrate surface
• recruit actin filament inside parasite linked to IMC
• link between surface protein, actin and myosin motor
  
  • shifts cell forward
• substrate cleavage allows parasite to glide

Question 10

evidence for apicomplexan motility model

Answer 10

• actin inhibitors prevent movement
  
  • cytochalasin blocks barbed end of actin
• overstabilisation of actin by jasplakinolide
  
  • blocks movement - actin turnover needed
• myosin knockouts - no movement (some residual activity)
• TRAP knock out in sporozoites prevents movement
• aldolase tetramer may link TRAP and actin
  
  • but shown not to be necessary

Question 11

gliding and plasmodium

Answer 11

• plasmodium very different in shape and size throughout life cycle but still use same motility mechanism
• gliding motility key at many stages

Question 12

stages of plasmodium invasion

Answer 12

• attachment to host cell
• reorientation with apex in fornt
• RBC penetration
• parasitophorous vacuole formation
  
  • junction formation, rhoptry secretion, coat shedding during movement
• movement is maintained because RBC won’t engulf parasite itself

Question 13

plasmodium invasion features

Answer 13

• many surface proteins identified but functions mainly not assigned
• diversity could be immunological - multiple invasion methods
• myosin combined with handshake interaction at tight junction pulls parasite in
• short process (few seconds)
• forces from the RBC too?
• coat shedding to distract immune system?

Question 14

non-apicomplexan invasion

Answer 14

• very different to apicomplexa like plasmodium
• parasite directs active uptake by the host
• use of endosomal pathway
  
  • fusion of vacuole with lysosome (fusigenic vacuoles)
  • suppress lysosomal activity for occupation
• can be delivered to macrophages as trojan horses
• use of complement receptors
• more in control

Question 15

T. cruzi invasion

Answer 15

• stimulates host cell to engulf and endocytose parasite by molecular interaction
• induce uptake by non-phagocytic cells
• enter phagocytic cells and avoid degradation
• suppress lysosomal function
• bursts vacuole and replciates freely in cytosol