section 9 - microfilaments (actin filaments)

stress fibres

in stationary cell

cortical actin

dividing

contractile ring

in ring

actin fibres

migratory cell

where actin filaments concentrated

actin bundles in microvilli

ring of actin fibres between adherens junctions

actin fibres at cell cortex

actin filaments depolymerised by

cytochalasin

actin filaments stabilised by

phalloidin

actin microfilaments in evolution

highly conserved

actin microfilaments as a dynamic polymer

G-actin monomers, F-actin fibres

master organiser for actin microfilaments

none

microfilaments role

dual role in eukaryote cells in conjunction with actin binding proteins

• structural

• force generation

structural role of microfilaments

responsible for cytoplasmic viscosity - rapid response to cell signals, local or global

force generation of microfilaments

polymerisation

contraction

vectoral transport

cell motility

treadmilling of actin polymer

more growth on one end of polymer - actin moves along filament - ATP dependent process (monomers lost)

G-actin

ATPase

villin

in brush border, actin filaments are cross linked by villin

Gelsolin/villin superfamily

each 6 domains

without extra domain attached to 6, actin severing protein

with extra domain attached to 6, actin bundling protein