cell adhesion Flashcards
how do cadherins bind to each other and how are they arranged?
- homophilic interaction
- ca2+ binding to extracellular hinge region stabilises cadherin –> enables cadherin to bind to cadherin on neighbouring cell
- cadherins exist as perpendicular arrays
adherens junction
large multi-protein complexes holding cells together
protocadherins
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
what is the structure of classical cadherins?
- single transmembrane domain
- intracellular domain
- extracellular repeated hinge regions
what is the structure of non-classical cadherins?
- homology in repeat regions
- other different arrangements of domains mediating protein-protein interactions
- (may have) multiple transmembrane domains
what are the three types of catenins?
p120-catenin
β-catenin
α-catenin
describe the expression of cadherins during early embryogenesis
- 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
what is the structure of Ca2+ independent CAMs?
- intracellular domain
- fibronectin type lll domains
- Ig like repeats
what is the RGD sequence
arginine-glycine-aspartate
what is the purpose of the RGD sequence?
required for the binding of fibronectin to integrin
what is the structure of integrins?
- 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
how does integrin become activated?
- inactive integrin = extracellular domain folded up
- extracellular domain binds to ECM and activates intracellular domain to activate its binding to talin
- talin binds —> extracellular domain unfolded —> more likely to interact with ECM
what is the actin cortex/cortical actin?
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
what is cytochalasin B and what is the effect of it when added to migratory cells?
- drug binding to + end of actin filaments
- blocks + end from having more actin added to it. actin filaments capped —> prevents migration
actin dissembles
what does rac kinase do?
activates Arp2/3 activity –> increases nucleation of actin filaments
Arp complex
- 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
what are the roles of endocytosis in motility?
- shapes chemotactic gradients
- activating receptors
- release adhesion to substrate
what does the podosome do?
anchors the cell
stress fibre
many strips of polymerised actin aligned together to provide strength
what is the role of profilin?
binds to actin monomers
enables ADP bound to monomer to be phosphorylated to ATP so they can be added to the growing filament
what is the role of gelsolin?
binds to + end and caps filament growth in that direction
what is the role of α-actinin filament?
binds filaments together to reinforce structure
what are the 3 branches of the rho family of GTPases?
- rac1
- rhoA
- cdc42
GAP
GTPase activating protein
increases GTPase activity of small GTPase –> shifts small GTPase to inactive state
GEF
guanine nucleotide exchange factor
promotes dissociation of GDP so GTP can bind
GDI
guanine nucleotide dissociation inhibitor
promotes slow dissociation of GDP —> keeps small GTPase in inactive state
Cdc42
activates WAVE proteins —-> activates Arp2/3 —> formation of new actin filaments
- formation of filopodia & actin spikes
Rac1
activates WASP proteins —-> activates Arp2/3 —-> formation of new actin filaments
- formation of lamellipodia
RhoA
activates rho kinase —-> phosphorylates myosin —-> increases myosin contractibility + actin stress fibre formation
how to create a constitutively active small GTPase mutant?
substitution of glutamine in switch 2
inactivates GTP hydrolysis
how to create a dominant negative small GTPase mutant?
substitution of P-loop
stops nucleotide binding
can bind to GEFs to mop them up
what is the CRIB motif
16 AA sequence in effector proteins active Rho family proteins bind to
