Jan 20 - Contraction and Chemotaxis

What is the form of the leading edge of a moving cell?

Branched actin network

What are the components of stress fibers?

Actin bundles with non-muscle myosin and integrins which have to do with the “feet“ of the cell

What is the form of the formins?

They look like a broken donut

What do formins do?

They rock up with the actin filament as it is polymerized the protein sits on the end of the actin filament and goes up as the actin grows and opposite if it shrinks

What does the FH1 domain do?

The FH1 domain is on the formin FH2 and grabs the actin from the solution

How stable are formins?

They are highly processive and add more than 10 000 monomers before detatching

What is myosin?

a motor protein

How are motor proteins like myosin able to produce a force?

Can convert chemical energy into mechanical energy due to conformational changes in the ATP domain which causes it to swing an arm and produce a force

What is a classic myosin assay?

Put the head of the myosin on a glass slide, actin filaments on top, then the myosin will do their conformational changes and the actin filaments can glide around on the surface of the glass. They produce force in the + end so that the - end is leading.

What is class I myosins good for?

Membrane association and endocytosis

What are class II myosins for?

Contraction

What are class III myosins good for?

Organelle transport (walks along a vesicle)

What os the form and function of non-muscle myosin-II?

Form bundles that pull actin filaments inward in an antiparallel conformation

What causes actin arrays to contract?

Myosin-II bundles. This causes the “back foot” of the cell to be pulled up

What are the structures of actin at the leading edge of a cell that is moving?

Dendritic cell network with cofilin, profilin etc.

Which structures are at the back of the migrating cell?

Stress fibers with non-muscle myosin II.

What is special about Dictyostelium?

Amoeba that aggregates with other amoeba upon starvation they then make a stalk that sticks upwards and produces a fruiting body that detaches in the hope that some can find somewhere better to eat

What do dictyostelium move toward?

Concentrated cyclic-AMP

Which are the three types of Rho family GTPases that can trigger 3 types of actin networks?

Stress fibers: Rho is dominant active

Lamellopodia: Rac is dominant active

Filopodia: Cdc42 is dominant active

What do Rho family GTPases translate signals into?

Changes in the actin cytoskeleton

What is the chain of events for effector proteins?

RhoGDP → GEF once extracellular signal goes into receptor and them GEF acts to replace with GTP → Rho GTP is now in a conformational change → produces effector proteins → Turns back when GAP removes a phosphate

How does Rho activate formins?

Relieving auto-inhibition of a folded up formin. Once the formin is unfolded, formin is linearized

How does Cdc42 activate Arp2/3 ?

Opening up WASp

What is a scratch assay?

Grow a lawn of cells on petri dish, put a big scratch in the middle of the dish and cells sense the existence of the wound and over time the wound will close

What are the steps to filopodia formation?

Cdc42 → WASp → Arp2/3 → Actin polymerization → Filopodia formation

What are the steps to Lamellipodia formation?

WAVE→ Arp2/3 → Actin polymerization → Lamellipodia

What are the main steps to stress fiber formation?

Rho→ Formin → Actin polymerization → Stress fiber formation

How does the cell know which edge to be the leading edge or not?

Cdc42 activation at the front of the

In front: Rac activation leading to Arp2/3 activation

IN the back: Rho activation which leads to myosin II activation

Different zones of activity due to chemical signals from activating and inhibiting