Lecture 16: The Role of Actin in Cell Movement

How can actin polymerization do work?

G-actin can form F-actin and release energy and released energy can result in membrane extension

What drugs destabilize actin?

Cytochalasin and Latrunculin

What does Cytochalasin do?

binds to the plus end and prevents ubunit addition

What does Latrunculin do?

binds G-actin and inhibits assembly into filaments; collapses the leading edge

What is Cytochalasin?

a fungal alkaloid

What is Latrunculin?

a toxin from sponges

What drug is an actin stabilizer?

Phalloidin

What is Phalloidin?

a cyclic peptide from poisonous mushroom

What does Phalloidin do?

binds, stabilizes actin filaments, and prevents depolymerization

True or False: Lamellipodia are filled with branched F-actin polymers.

true

What is the experiment that led to the conclusion that polymerization can drive movement?

the experiment with Listeria monocytogenes

What is the Listeria monocytogenes experiment?

-Actin forms comet tails on one end of the bacterium

-Actin comet tails allows bacteria to move from one cell to another without the immune system noticing

-Actin comet tails allow the bacteria to go through the plasma membrane

What was the in-vitro Listeria experiment?

-Cells are broken open and made into a cell extract

-Bacteria are added to the cell extract

-Bacteria moves within the cell extract

Does the in-vitro Listeria experiment conclude whether polymerization is sufficient to drive motion?

no, it doesn’t

What are the 2 possible models for Listeria movement?

-No motor proteins and polymerization drive movement

-Motor proteins are required, and polymerization is necessary but not sufficient for movement

What is the protein in Listeria that is necessary for movement?

ActA

In a bacteria with LOF allele in the ActA gene, what happens?

the bacteria cannot move

Where is ActA displayed in the cells?

on the same side of as the actin comet tails

True or False: ActA is not a motor protein.

true

What is the experiment that conlcuded if ActA is sufficient for movement?

-Researchers took a plastic bead and attached ActA to one side

-The bead moved

What did the ActA experiment conclude?

actin assembly is sufficient to drive movement in bacteria

What is present at the leading edge of a cell?

actin

What is not present at the leading edge?

motor proteins

How does polymerization move a membrane?

it’s currently unknown!