REINHART 4 Flashcards
what is the structure of P selectin
binds to actin filaments through anchor proteins in the cytosol
has a lectin domain and an EGF like domain in the ECM (extracellular matrix)
it is calcium dependent
what are the different types of selectins
oligosaccharide binding proteins
L selectin=lymphocytes (white blood cells)
E selectin= activated endothelial cells
P selectin=platelets, endothelial cells
where are endothelial cells found?
present in the intima layer of blood vessels
what do lymphocytes do and how do they move through the blood stream
remove impurities
constantly circulate
extremely fast
need to slow down
what happens at the inflammation site
endothelial cells express selectins, oligosaccharides are located on lymphocytes
what is the nature of the bond between selectins and oligosaccharides
not a very strong integration
how are lymphocytes pulled out of the blood vessels into the tissue?
white blood cells roll along the endothelial cells, and by strong interaction (integrin dependent) they have a strong interaction
but they move so fast that there is sequential unbinding and binding.
this makes the blood cells roll
till they are slowed down enough and go to the inflamed tissue to carry out their function, exit the blood vessel
what is the structure of calcium independent cell adhesion molecules
different types of ways they are attached to the membrane (long C terminus, short C terminus, GPI anchor, or not attached at all)
have a fibronectin type III domain
have an Ig like domain
have disulfide bonds that hold them together
what are disulfide bonds indicative of
extracellular domains
what two proteins are frequently co expressed together?
cadherins and ig like cell adhesion molecules
what are the different types of cell adhesion molecules
N CAM (neural) = fine tuning of interactions during development and regeneration
I CAM: intercellular
V CAM: vascular
what are the non junctional adhesion mechanisms (transient) mechanisms of cell attachment?
cell matrix adhesion:
integral membrane proteoglycan
integrins
cell cell adhesion:
cadherins
Ig like CAMs
itegrins
selectins
what are the different types of junctional adhesion mechanisms (permanent)?
cell matrix adhesion
hemidesmosomes (integrins)
focal adhesions (integrins)
cell cell adhesion:
actin filaments
intermediate filaments
tight junctions (claudins)
adhesion belt (cadherins)
desmosomes (cadherins)
gap junction (connexins)
what subunits do integrins possess?
alpha and beta subunits
heterodimers
in which types of organisms are integrins not found?
prokaryotes
plants
fungi
how many units of each subunit of integrins do C. elegans have?
two alpha subunits and one beta subunit -> form two integrins
how many units of each subunit of integrins do vertebrates and how many theoretical possibilities does that make?
18 alpha subunits
8 beta subunits
18*8=144 theoretical possibilities
how many different integrins do vertebrates have?
24 integrin heterodimers
what do integrins participate in?
cell matrix adhesion
cell cell adhesion
cell aggregation
what do leukocyte specific receptors do?
cell cell recognition
recognise IG superfamily counter receptors
what do collagen receptors do?
recognised ECM molecules
what do laminin receptors do?
major proteins in basement membrane
what do RGD receptors do?
RGD motifs in ECM motifs
i dont really know what i was trying to say with this one
how are the subunits that can bind to multiple things made to be different for each of those binding combinations?
alternative splicing
what do integrins need to work?
calcium
what is the structure of integins
very small C terminus in the cytosol (20-50AAs)
alpha subunit:
Furin cleavage, held together with disulfide bond
alpha chain
very large N terminus doain
beta subunit:
cysteine rich domains
beta chain
matrix binding domain with mental binding sites
the side is 90-160kDa
what types of TM proteins are integrins?
type I: C in cytosol N, in matrix
what are most integrins connected to and how?
connected via intracellular anchor proteins to actin (except a6b4 intermediate filaments which bind laminin)
what does RGD stand for and what are the charges?
R: arginine, positively charged
G: glycine, neutral
D: aspartic acid, negatively charged
what can be added to RGD to make a synthetic circular RGD
phenylalanine, to make cyclo RGDF
what amino acid makes contact with the metal on the beta head domain
aspartic acid
what do integrin ligand often contain
accessory or synergy sites for receptor binding
what sites does fibronectin have
fibronectin is an integrin ligand
synergy site (Fn9)
RGD (Fn10)
RGD integrin binding site domain= how it binds to integrin
how do unbound integrins go through the plasma membrane
diffuse freely
how are integrins activated when they are not constitutively active
extracellular ligand binding: outside in activation and/or from within the cell via the integrin cytoplasmic tail
inside out activation
what are not constitutively active integrins important for?
cell aggregation (adhesion of circulating platelets to soluble matrix)
cell cell adhesion (leukocytes and inflammation)
what are the different conformation of when the ligand is bound vs unbound
unbound: bent, inactive
bound: straight, active
how does outside in integrin activation happen
via extracellular ligand binding to the bend inactive conformation (weak interaction)
straightening of alpha and beta chains
ligand will bind much stronger
conformational change in beta subunit head domain
separation of the entire alpha and beta subunits (move away from each other)
active integrin
which integrin mediates blood platelet aggregation
aIIb3
via binding to fibrinogen
the activation of this integrin is necessary
how does the activation of aIIb3 integrin happen?
via exposure to collagen IV or thrombin (outside blood vessels)
what happens once aIIb3 integrin is activated?
binds fibrinogen, and then you have the formation of a blood clot
what is the size of integrin cytosolic domains?
generally less than 50 amino acids
what is the function of the cytosolic domain of integrin
- sites of interaction with, and linkage to, the cytoskeletal and signalling partners of integrins
- the cytoplasmic domains can regulate the activation state of integrins
what does the deletion of the conserved membrane proximal segment from either subunit lead to
activation
what do point mutations in some of the cytosolic domain sequences lead to?
activation
what does talin do?
binds to beta subunit
disrupts the ionic salt bridge ->
separation of alpha and beta subunits
activation
how can talin be activated?
talin can be activated for binding to beta tails by cleavage to release the integrin binding head
talin also can be activated by interaction with phosphoinositol-4,5-bisphosphate (PIP2)
