Actin Binding Protiens And Cell Motility Flashcards
What is the cell cortex/ actin cortex
A network of actin on the inner face of the plasma membrane that can enable cells to:
crawl/move
Undergo phagocytosis
And constrict during cell division
What are actin binding protiens
They are protiens that bind to actin and regulate the assembly/disassembly and rearrangement of actin networks
This include more then 100 diff protiens
What are the 8 types of actin binding proteins
Filament nucleating
Monomer-sequestering
End blocking (capping)
Monomer polymerizing
Depolymerizing
Cross linking and bundling
Filament severing
Membrane binding
What are filament nucleating protiens
Filament nucleation (formation) of actin filament is slow so these protiens enhance the rate the they’re formed when a seed filament if present
What are the two categories of filament nucleating protiens
The ARP 2/3 complex
Formins
What does the ARP 2/3 complex do
It binds to the sides of an existing actin filament meaning it begins to create branches
It remains at the pointed end of the new branch and has a similar structure to actin monomers
What do formins do
They make UNBRANCHED filaments by staying accosiated with the barbed end of the actin filimants
They promotes fast ELONGATION of the the actin filaments
What are monomer sequestering protiens
They bind to actin atp monomers and prevent them from being added to the growing actin filament
Basically hide them away from the actin filament
This means they can alter the levels of available monomers in certain regions and keep them in separate actin pools for use later
Ex thymosins
What are endblocking (capping) protiens
The regulate the length of the actin filaments by binding at either end (barbed or pointed, + or -)
If capped at the barbed end the pointed end gets degraded but if capping protien at the pointed end it doesn’t get degraded
What are monomer polymerizing protiens
They bind to actin monomers to promote the growth of actin filaments
They do this by promoting the replacement of adp with atp. Since the monomers only fall off the filament when they have adp.
If we quickly change it to atp the monomers that fall off the pointed end can quickly get added back into the barbed end
Ex. Profilin
What are depolymerizing protiens
They bind to actin adp at the pointed end to speed up their depolymerization (dissociation)
Ex. Cofilin
What are cross linking and bundling protiens
The have multiple acting binding sites that let them change the 3D organization of filaments
They can cause filament to be either parallel (bundled) or perpendicular (cross linked) to each other
Ex. Bundling: vilin and fimbrin
Cross linking : filamin
What are filament severing protiens
Break an existing actin filament in two
Ex. Gelsolin, cofilin
What are membrane binding protiens
They link actin filaments to the plasma membrane
This allows the plasma membrane to protrude outward (cell locomotion) or inward (phagocytosis)
Ex. Spectrin which connects actin to the red blood cell membrane
What does profilin do
Polymerizes actin monomers
What does cofilin do
Depolymerizes actin monomers
What does arp 2/3 do
Makes branched filament on the actin filament
What is the first step in cell motility
- The movement of the cell begins by a protrusion of the cell in the direction is wants to move
Called the lamellipodium
What is the second step in cell motility
A part of the protrusion (lamellapodium) anchored to the surface that is moving on
What is the 3rd step in cell motility
The bulk of the cell is pulled to the front while the parts connected to the surface stay in place
What is the fourth step in cell motility
The adhesive contacts to the surface break and the trailing edge (tail) of the cell retracts
What if the first few step in how the lamellipodium forms
First a stimulus is received at the cell surface
Then the arp 2/3 complex near the stimulation gets activated
The arp 2/3 binds to the side of an actin filament and the actin monomers bind to it to make a new branch
The polymerization of the new branch is promoted by profilin
What are the last few step in how the lamellipodium forms
More new ARP 2/3 complexes bind to the side of actin filaments to make new branches
the old branches are capped at their barbed ends (where growth is happening) to make the filaments short and stable
The newer branches keep growing and pushed the membrane of the lamellipodium forward
The older capped filaments/ branches are disassembled on their pointed end which is enhanced by cofilin
What are traction forces in relation to cell motility
When the cell grips the surface at adhesion pints in the membrane called focal adhesions
What are focal adhesions in relation to cell motility
These are structures in the cell membrane where integrin protiens connect to the actin filaments
What are integrin protiens in relation to cell motility
These are transmembrane protiens in the cell that mediate the interaction between the actin filaments in the cell and the surface outside the cell
They link the inside to the outside but are temporary, not always linked to one same spot
What is at the rear of the lamellipodium and what does it do
Myosin
uses contraction forces to pull the bulk of the cell forward
