Lecture 19 Flashcards
What are Catenins? which of the 3 types is most important?
catenins are small proteins that serve as a major interface between cytoplasmic end of cadherins and the cytoplasmic actin
alpha catenins are the type that directly binds to actin (beta and gamma plakoglobin catenins only bind to the cytoplasmic end of a cadherin)
Describe the intracellular and extracellular portions of cadherins
The extracellular portion has multiple copies of the cadherin domain motif and the intracellular portion is much more variable
What type of binding typically occurs between cadherins? where does this occur?
homophillic
at the N-terminal tips of the cadherin molecule
describe the distribution/structure of the bond between cadherin molecules and how this affects the strength of the bonds they form.
Cadherins are clustered side-by-side on the same cell via N-terminal head regions and intracellular tail attachments to anchoring proteins
the bonds are weak, due to low affinity, individually but strong in larger numbers
What ion is crucial for cadherin bonds? describe the role this ion plays
Ca2+ ions bind to sites near the hinges between the repeated cadherin domain and give it rigidity
Ca2+ ions also increase the affinity their extracellular portion has for cadherin-cadherin binding
describe how cadherin bonds are dissociated and how easily this is accomplished
When Ca2+ is removed, the cadherin repeats lose rigidity, and a conformation change in the N-terminal that weakens affinity for the N-terminal of the other cadherin and the bond dissociates (pretty easy to do)
what are the 3 forms of catenins? which is most important and why?
Beta, gamma/plakoglobin, and alpha catenins
alpha catenins are the most important bc they are the one that directly binds to cytoplasmic actin
what role do cadherins play in cell sorting? why is this important?
Cadherin-dependent homophilic adhesions mediate “sorting out” and allow cells of a similar type to stick together and stay segregated from different cell types in a “highly selective” manner
this is a crucial step in embryonic development
what is special about the cadherin properties of neural crest cells?
they alter their adhesive properties in order to migrate away from the epithelium and differentiate into a variety of different cell types
How is actin-based motility of cells made possible? what cell makes this possible?
catenins serving as the link between cytoplasmic actin and the extracellular portions of cadherins are what makes actin-based motility possible
What is the junction type and function of a desmosome?
They are macular adheren spot junctions that bind adjacent cells together on their lateral domains
describe selectins and their main function in cell-cell adhesion
a member of the lectin family that binds to carbohydrates via its extracellular CRD (carbohydrate recognition domain) and is involved in leukocyte extravasation
What are the 3 types of selectins? state their respective associations
P-Selectins: associated with platelets
E-Selectins: associated with activated endothelial cells
L-selectins: associated with leukocytes
Define the role of ICAMs in cell-cell adhesion
(intercellular cell adhesion molecule) integrin receptor member of the Ig superfamily that facilitates transendothelial migration of leukocytes by binding to them and stopping their “rolling”
Define the role of VCAMs in cell-cell adhesion
(vascular cell adhesion molecule) integrin receptor member of the Ig superfamily that facilitates vascular migration of leukocytes by binding to them and stopping their “rolling”
describe the basics of a tight junction
they are junctions that form a “seal” between cells via occluding junctions that prevent paracellular transport of molecules to ensure a vectoral transfer of nutrients between membrane domains (found in epithelia and endothelial sheet)
Describe the structure of a tight junction
each sealing strand has a long row of 4-pass transmembrane adhesion proteins (claudin being the most functional, and occludin) that interact between the 2 cell’s PM’s
ZO protein anchors tight junctions to the actin cytoskeleton
State and describe the 3 functions of tight junctions
Barrier Function: the extracellular portions of tight-junction strands function as a “ziplock” with diversified permeability
Fence Function: encircles the top of cells in order to establish the border between apical and basolateral domains of a cell in order to limit the lateral diffusion of lipids and proteins
Signaling Function: the cytoplasmic portions of tight-junctions serve as a magnet that attracts various PDZ-containing proteins
