Cell adhesion molecule

Cell Adhesion Molecules (CAMs) are proteins located on the cell surface^[1] 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 5 protein families: Ig (immunoglobulin) superfamily (IgSF CAMs), the integrins, the cadherins, the selectins and the lymphocyte homing receptors.

One classification system involves the distinction between calcium-independent CAMs and calcium-dependent CAMs.^[2]

Calcium-independent

IgSF CAMs

Immunoglobulin superfamily CAMs (IgSF CAMs) are either homophilic or heterophilic and bind integrins or different IgSF CAMs.
Here is a list of some molecules of this family:

• NCAMs Neural Cell Adhesion Molecules
• ICAM-1 Intercellular Cell Adhesion Molecule
• VCAM-1 Vascular Cell Adhesion Molecule
• PECAM-1 Platelet-endothelial Cell Adhesion Molecule
• L1
• CHL1
• MAG
• Nectins and nectin-like molecules

Integrins

The Integrins are a family of heterophilic CAMs that bind IgSF CAMs or the extracellular matrix. They are heterodimers, consisting of two noncovalently-linked subunits, called alpha and beta. Eighteen different alpha subunits that combine with 9 different beta subunits to form twenty-four known integrins; however not all combinations are observed.

Lymphocyte homing receptors

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

Calcium-dependent

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. They are calcium-dependent. 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.

References