cell adhesion

Question 1

how do cadherins bind to each other and how are they arranged?

Answer 1

• homophilic interaction
• ca2+ binding to extracellular hinge region stabilises cadherin –> enables cadherin to bind to cadherin on neighbouring cell
• cadherins exist as perpendicular arrays

Question 2

adherens junction

Answer 2

large multi-protein complexes holding cells together

Question 3

protocadherins

Answer 3

highly variable non-classical cadherins found in the nervous system
alternative splicing gives rise to multiple isoforms
- specify synapses in the brain –> confers complex connectivity
- neurite self avoidance behaviour

Question 4

what is the structure of classical cadherins?

Answer 4

• single transmembrane domain
• intracellular domain
• extracellular repeated hinge regions

Question 5

what is the structure of non-classical cadherins?

Answer 5

• homology in repeat regions
• other different arrangements of domains mediating protein-protein interactions
• (may have) multiple transmembrane domains

Question 6

what are the three types of catenins?

Answer 6

p120-catenin
β-catenin
α-catenin

Question 7

describe the expression of cadherins during early embryogenesis

Answer 7

• E-cadherin - first cadherin expressed in early embryo. involved in compaction of cells.
• mesoderm cells lose e-cadherin expression because they move inside the embryo so must dissociate from outside
• n-cadherin expressed in neural tube
• e-cadherin expressed in epithelium
• cadherin 6B expressed in junction region
• cadherin 7 expressed in neural crest cells

Question 8

what is the structure of Ca2+ independent CAMs?

Answer 8

• intracellular domain
• fibronectin type lll domains
• Ig like repeats

Question 9

what is the RGD sequence

Answer 9

arginine-glycine-aspartate

Question 10

what is the purpose of the RGD sequence?

Answer 10

required for the binding of fibronectin to integrin

Question 11

what is the structure of integrins?

Answer 11

• form heterodimers
• alpha subunit is cleaved and then held together via disulphide bonds
• extracellular cysteine rich domains forming disulphide bridges —> structure
• matrix binding domain interacts with ECM
• binds to Mg2+, Ca2+ etc. –> activating function
• talin and vinculin anchors intracellular domain to actin filaments

Question 12

how does integrin become activated?

Answer 12

1. inactive integrin = extracellular domain folded up
2. extracellular domain binds to ECM and activates intracellular domain to activate its binding to talin
3. talin binds —> extracellular domain unfolded —> more likely to interact with ECM

Question 13

what is the actin cortex/cortical actin?

Answer 13

actin skeleton underneath membrane –> supports outline of cell and maintains shape
aids tension as cell is migrating
prevents cell from being squashed by neighbouring cells

Question 14

what is cytochalasin B and what is the effect of it when added to migratory cells?

Answer 14

• drug binding to + end of actin filaments
• blocks + end from having more actin added to it. actin filaments capped —> prevents migration
  actin dissembles

Question 15

what does rac kinase do?

Answer 15

activates Arp2/3 activity –> increases nucleation of actin filaments

Question 16

Arp complex

Answer 16

• made up of Arp2 and Arp3 + other proteins
• bind at - end of actin filaments
• promote actin polymerisation
• nucleate actin filaments
• resemble actin
• can form complexes as well as filaments

Question 17

what are the roles of endocytosis in motility?

Answer 17

• shapes chemotactic gradients
• activating receptors
• release adhesion to substrate

Question 18

what does the podosome do?

Answer 18

anchors the cell

Question 19

stress fibre

Answer 19

many strips of polymerised actin aligned together to provide strength

Question 20

what is the role of profilin?

Answer 20

binds to actin monomers

enables ADP bound to monomer to be phosphorylated to ATP so they can be added to the growing filament

Question 21

what is the role of gelsolin?

Answer 21

binds to + end and caps filament growth in that direction

Question 22

what is the role of α-actinin filament?

Answer 22

binds filaments together to reinforce structure

Question 23

what are the 3 branches of the rho family of GTPases?

Answer 23

• rac1
• rhoA
• cdc42

Question 24

GAP

Answer 24

GTPase activating protein

increases GTPase activity of small GTPase –> shifts small GTPase to inactive state

Question 25

GEF

Answer 25

guanine nucleotide exchange factor

promotes dissociation of GDP so GTP can bind

Question 26

GDI

Answer 26

guanine nucleotide dissociation inhibitor

promotes slow dissociation of GDP —> keeps small GTPase in inactive state

Question 27

Cdc42

Answer 27

activates WAVE proteins —-> activates Arp2/3 —> formation of new actin filaments
- formation of filopodia & actin spikes

Question 28

Rac1

Answer 28

activates WASP proteins —-> activates Arp2/3 —-> formation of new actin filaments
- formation of lamellipodia

Question 29

RhoA

Answer 29

activates rho kinase —-> phosphorylates myosin —-> increases myosin contractibility + actin stress fibre formation

Question 30

how to create a constitutively active small GTPase mutant?

Answer 30

substitution of glutamine in switch 2

inactivates GTP hydrolysis

Question 31

how to create a dominant negative small GTPase mutant?

Answer 31

substitution of P-loop
stops nucleotide binding
can bind to GEFs to mop them up

Question 32

what is the CRIB motif

Answer 32

16 AA sequence in effector proteins active Rho family proteins bind to