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Cell Adhesion Molecules | Structure and Types

Cell adhesion molecules (CAMs) are a subset of cell surface proteins that are involved in the binding of cells with other cells or with the extracellular matrix (ECM), in a process called cell adhesion. In essence, CAMs help cells stick to each other and to their surroundings. CAMs are crucial components in maintaining tissue structure and function. In fully developed animals, these molecules play an integral role in generating force and movement and consequently ensuring that organs are able to execute their functions normally. CAMs are typically single-pass transmembrane receptors and are composed of three conserved domains: an intracellular domain that interacts with the cytoskeleton, a transmembrane domain, and an extracellular domain. These proteins can interact in several different ways. The first method is through homophilic binding, where CAMs bind with the same CAMs. They are also capable of heterophilic binding, meaning a CAM on one cell will bind with different CAMs on another cell. There are four major superfamilies or groups of CAMs: the immunoglobulin super family of cell adhesion molecules (IgCAMs), Cadherins, Integrins, and the Superfamily of C-type of lectin-like domains proteins (CTLDs). Proteoglycans are also considered to be a class of CAMs. One classification system involves the distinction between calcium-independent CAMs and calcium-dependent CAMs.[7] Integrins and the Ig-superfamily CAMs do not depend on Ca2+ while cadherins and selectins depend on Ca2+. In addition, integrins participate in cell–matrix interactions, while other CAM families participate in cell–cell interactions. Immunoglobulin superfamily CAMs (IgSF CAMs) is regarded as the most diverse superfamily of CAMs. This family is characterized by their extracellular domains containing Ig-like domains. Integrins, one of the major classes of receptors within the ECM,mediates cell–ECM interactions with collagen, fibrinogen, fibronectin, and vitronectin. Integrins provide essential links between the extracellular environment and the intracellular signalling pathways, which can play roles in cell behaviours such as apoptosis, differentiation, survival, and transcription. The cadherins are homophilic Ca2+ dependent glycoproteins. The classic cadherins (E-, N and P-) are concentrated at the intermediate cell junctions, which link to the actin filament network through specific linking proteins called catenins. The selectins are a family of heterophilic CAMs that are dependent on fucosylated carbohydrates, e.g., mucins for binding. The three family members are E-selectin (endothelial), L-selectin (leukocyte), and P-selectin (platelet).