Question

Describe the structure of a cadherin and contrast that basic structure with ONE of the other types of cell adhesion molecules (immunoglobulin superfamily, integrins and selectin).

Answer 1

Cadherins

Cadherins are a class of type 1 transmembrane protein. This is calcium dependent adhesion molecule plays a important role in cell adhesion by forming desmosoms.

This cell adhesion molecule (CAM) is homotype. That is one CAM directly binds with same CAM.Cadherin superfamily includes cadherins, protocadherins, desmogleins and desmocollins. In their structure they share cadherins repeats which are extracellular calcium dependent binding domains . It has been observed that cells containing the specific cadherin subtype tend to cluster together to the exclusion of other types, both in cell structure and during development. Eg. Cells containing N-cadherin tend to cluster with other N-cadherin expressing cells.

Cadherin tails are anchored to actin bundles in the cytoskeleton by the complex called catenins( beta catenins, a component of the Wnt signalling pathway provides the potential link between cell signalling and cell association.

Three glycoproteins mediates the calcium dependent cell adhesions ( desmoglein I , desmocollin I and II) and four non glycosalated proteins located in the attachment plaque( desmoplakin I and II, pakoglobin and basic polypeptide)

There are 3type of cadherins

E cadherin found in epithelial cell

N cadherin found in neuron, muscle tissue

P cadherin found in placenta, epidermis

They all have a similar structure with five extracellular cadherin repeats , a transmembrane domain and a intracellular domain.

Integrins

They are cell surface receptors that mediates adhesion to the extracellular matrix and cell -cell interaction.

Individual integrin bind with more than one ligand.

These are transmembrane protein and heterodimers of alpha and beta subunits. Both alpha and beta subunits show sno homology to each other. There are 18 alpha and 8 beta subunit type , however there are only 24 types found in human body .

Contrast :

*Cadherins are chain like structure

Integrins contains alpha and beta domains.

*Cadherins are streached out only when bound to calcium .

Integrins are also depends on calcium and mostly depends on magnesium.

*Cadherins form interaction between two cells.

Integrins form interaction between cells to ECM and cell-cell interaction.But mostly they form interaction between cells to ECM . And more parts of integrin are present in ECM.

* Cadherins are homotype .

Integrins are heterotype.

*

Both are transmembrane proteins.

Both form binding with actin linked matrix.

Contrast with each CAM: