Cell Adhesion Molecules: Types and Functions

Cell Adhesion Molecules (CAMs): Types and Functions

Structurally, there are five families of CAMs: Cadherins, Immunoglobulin superfamily, Integrins, Selectins, and Proteoglycans.

Cadherins

Cadherins are monomeric molecules, which are receptors that bind *homophilically* (to identical cadherins) or *heterotypically* (to different cadherins) expressed on cells for cell-cell contact. Their action is calcium and temperature-dependent. A cell can express more than one type of cadherin. At least twelve types are known, but the most studied are:

• E-cadherin: Present in epithelia of various tissues, such as liver and kidney.
• N-cadherin: Found in neural tissue and heart muscle.
• P-cadherin: Found in the placenta.

Cadherins allow cell adhesion and maintenance of tissues, the persistence of intercellular spaces, embryonic development, embryonic growth, the introduction of blastomeres, and morphogenesis.

Immunoglobulin Superfamily (IgSF) CAMs

These are cell receptors that include a large number of proteins with diverse functions and tissue distribution. All share a region of 60 to 100 amino acids between two domains, which are arranged in two antiparallel disulfide-bonded bands. These bands form an immunoglobulin fold, which is a characteristic domain. All members of this family have at least one of these domains. Some of these CAMs are secreted and are no longer surface receptors. IgSF CAMs can be monomeric, dimeric, or heterodimeric. They can bind *homophilically* or *heterophilically* and can react with *homotypic* or *heterotypic* cells.

Integrins

Integrins are heterodimeric membrane receptors that mediate cell-cell and cell-matrix interactions. They are made up of two different chains associated non-covalently: the alpha subunit and the beta subunit.

Selectins (LEC-CAMs)

Selectins, or LEC-CAMs, are monomeric adhesion receptors with an amino-terminal extracellular region containing a lectin-like portion, a domain similar to epidermal growth factor (EGF), and several complement regulatory protein-like structures. Hence, the name LEC-CAMs: L (Lectin-like), E (EGF-like), and C (Complement regulatory protein-like).

Proteoglycans

This family of proteins has, in common, the presence of one or more glucose-amino-glycan side chains, through which they interact with matrix proteins and growth factors. Proteoglycans are part of the collagen matrix, but some are expressed on cell surfaces, allowing them to join the matrix. Among these molecules is Syndecan.