Focal adhesion

Focal adhesions are integrin-containing, multi-protein structures that form mechanical links between intracellular actin bundles and the extracellular substrate in many cell types.

Focal adhesions are large, dynamic protein complexes through which the cytoskeleton of a cell connects to the ECM.

They are limited to clearly defined ranges of the cell, at which the plasma membrane closes to within 15 nm of the ECM substrate.

One example of their important role is in the immune system, in which white blood cells migrate along the connective endothelium following cellular signals to damaged biological tissue.

Within the cell, the intracellular domain of integrin binds to the cytoskeleton via adapter proteins such as talin, α-actinin, filamin, vinculin and tensin.

The dynamic assembly and disassembly of focal adhesions plays a central role in cell migration.

[5] Once in place, a focal adhesion remains stationary with respect to the extracellular matrix, and the cell uses this as an anchor on which it can push or pull itself over the ECM.

This is the source of traction required for migration; the focal adhesion acts as a molecular clutch when it tethers to the ECM and impedes the retrograde movement of actin, thus generating the pulling (traction) force at the site of the adhesion that is necessary for the cell to move forward.