Lecture 7: Migration

Thirty flashcards covering the molecular structure, regulation, and functional roles of Rho GTPases (RhoA, Rac1, Cdc42) in cell migration and signaling.

What is the molecular mass of the small GTPases discussed in the lecture?

$$21\,kDa$$

To which large group of signaling proteins do small Rho GTPases belong?

The Ras superfamily

What fundamental change occurs to small GTPases upon their activation?

They change conformation

What nucleotide must a small GTPase be bound to in order to be considered "signaling active"?

$$GTP$$

Which nucleotide is bound when a GTPase is in its inactive state?

$$GDP$$

What is the function of Guanine Nucleotide Exchange Factors (GEFs)?

They accelerate the exchange of $GDP$ for $GTP$

How much do GEFs accelerate the exchange process compared to baseline?

$10$-$10^7$ fold

What is the primary role of GTPase Activating Proteins (GAPs)?

They accelerate hydrolysis of $GTP$ to $GDP$ to turn off signaling

How much do GAPs accelerate the hydrolysis of $GTP$?

$2000$-$10^5$ fold

Which ion is essential for nucleotide binding according to the Switch region diagram?

$$Mg^{2+}$$

What are the residue positions for Switch 1 in the GTPase structure?

Residues $25$-$39$

What are the residue positions for Switch 2 in the GTPase structure?

Residues $57$-$75$

What specific residue acts as the catalytic glutamine in the hydrolysis mechanism?

$$Q61$$

What sequence defines the P-loop responsible for counteracting negative charge at phosphates?

$$12GxxGKT17$$

How does the $G12V$ mutation affect the GTPase structurally?

It pushes $Q61$ out of position and disturbs the P-loop

What amino acid from $p50$ is identified as the "Arg finger" involved in hydrolysis stabilization?

$$Arg\,85$$

What is the effect of the $T17N$ mutation on a GTPase?

It acts as a dominant negative

According to the lecture, which protein domain is found in DOCK-family GEFs?

DOCK-family domain (noting Dbl-homology and Sec7 are also mentioned for GEFs)

Which GTPase is specifically responsible for the formation of Filopodia?

$$Cdc42$$

Which GTPase controls the formation of Lamellipodia during migration?

$$Rac1$$

Which GTPase is the primary driver of Stress Fibres and actomyosin contraction?

$$RhoA$$

What downstream effector does active $RhoA$ use to stimulate contraction?

$$RhoA\,Kinase$$

What part of the myosin molecule is phosphorylated by $RhoA\,Kinase$ to induce contraction?

Myosin Light Chain

Which two GTPases are categorized as protrusive signals?

$Cdc42$ and $Rac1$

What is the relationship between $Rac$ and $RhoA$ during protrusion at the cell front?

$RhoA$ is suppressed where $Rac$ leads to maximum protrusion

How many Dbl family GEFs are approximately known?

Over $70$

What contact is formed between $Tiam1$ and its target GTPase?

$9$ residues from the body and Switch 2 form contiguous contact

Why is the $Rac\,W56F$ mutant significant in studying GEF specificity?

It is $Tiam1$ insensitive but $ITSN$ sensitive

What function is attributed to the GTPase Ran in the notes?

Nuclear import and Mitotic spindle organisation

What role do Rab proteins play within the cell?

Endosomal trafficking, membrane budding, and vesicular trafficking