Cell adhesion molecule

Cell Adhesion Molecules (CAMs) are proteins located on the cell surface involved with the binding with other cells or with the extracellular matrix (ECM) in the process called cell adhesion.

These proteins are typically transmembrane receptors and are composed of three domains: an intracellular domain that interacts with the cytoskeleton, a transmembrane domain, and an extracellular domain that interacts either with other CAMs of the same kind (homophilic binding) or with other CAMs or the extracellular matrix (heterophilic binding).

Families of CAMs
Most of the CAMs belong to four protein families: Ig (immunoglobulin) superfamily (IgSF CAMs), the integrins, the cadherins, and the selectins.

One classification system involves the distinction between calcium-independent CAMs and calcium-dependent CAMs.

IgSF CAMs
Immunoglobulin superfamily CAMs (IgSF CAMs) are either homophilic or heterophilic and bind integrins or different IgSF CAMs.

Lymphocyte homing receptors
These are also known as addressins. Two well known examples are CD34 and GLYCAM-1.

Integrins
The Integrins are a family of heterophilic CAMs that bind IgSF CAMs or the extracellular matrix. They are heterodimers, called alpha and beta. Eighteen different alpha subunits that combine with 8 different beta subunits to form twenty-four known integrins; however not all combinations are observed.

Cadherins
The cadherins are a family of homophilic CAMs, Ca2+-dependent. The most important members of this family are E-cadherins (epithelial), P-cadherins (placental), and N-cadherins (neural).

Selectins
The selectins are a family of heterophilic CAMs that bind fucosylated carbohydrates, e.g., mucins. The three family members are E-selectin (endothelial), L-selectin (leukocyte), and P-selectin (platelet). The best-characterized ligand for the three selectins is P-selectin glycoprotein ligand-1 (PSGL-1), which is a mucin-type glycoprotein expressed on all white blood cells.