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Adherens junctions provide strong mechanical attachments between adjacent cells through the linkage of cytoplasmic face with cytoskeleton.
Describe the characteristics of adherens junctions
Adherens junctions are involved in a number of critical functions, including providing additional structural support. For example, they hold cardiac musclecells tightly together as the heart expands and contracts.
Adherens junctions are built primarily from cadherins, whose extracellular segments bind to each other and whose intracellular segments bind to catenins. Catenins are connected to actin filaments.
Adherens junctions are also referred to as zonula adherens,
intermediate junction, or as belt desmosomes.
Zonula means small zone or belt-like, and adherens refers to adhesion
(sticking together). As a result, the
zonula adherens often runs like a belt around the entire cell in a continuous fashion, and it acts as an adhesion belt.
Location and Function
This type of cell junction is located right below tight
junctions and provides a strong bond between the sides of adjacent epithelial
cell membranes. While other junctions,
like tight junctions, provide some support for and fusion of adjacent cells,
their resistance to mechanical stress is relatively small compared to the much stronger
Structure and Composition
The zonula adherens is composed of several different proteins:
The actin microfilaments of the cytoskeleton (the internal
skeleton of the cell).
Anchor proteins, found inside each cell. These are called alpha-catenin, beta-catenin,
gamma-catenin (aka plakoglobin), vinculin, and alpha-actinin. They link the actin microfilaments to the
Cadherins, namely E-cadherin. These are transmembrane adhesion proteins, whose
main portions are located in the extracellular space.
The extracellular part of one cell’s cadherin binds to the extracellular
part of the adjacent cell’s cadherin in the space between the two cells. Each
cell’s cadherin molecule also contains a tail that inserts itself inside its
(within the cell) tail then links up to catenin proteins to form the cadherin–catenin
complex. This complex binds to vinculin
and alpha-actinin; these two proteins
are what link the cadherin–catenin complex to the cell’s internal skeletal
framework (the actin microfilaments).
The extracellular portions of the cadherin molecules of
adjacent cells are bonded together by calciumions (or another protein in some
cases). This means that the functional
as well as morphological integrity of the adherens junctions are calcium
dependent. If you were to remove calcium
from the equation, this type of cell junction would disintegrate as a