Cell adhesion molecules (CAM) have four major superfamilies or groups: immunoglobulin superfamily (IgCAM) of cell adhesion molecules, cadherin, integrin and lectin-like domain protein C-type superfamily (CTLD). Proteoglycans are also considered to be a class of CAMs.

IgSF CAMs (Immunoglobulin-like Cell Adhesion Molecules)

IgSF CAM (immunoglobulin-like cell adhesion molecule) is a cell adhesion molecule belonging to the immunoglobulin superfamily. It is considered to be the most diverse superfamily of CAM. This family is characterized in that its extracellular domain comprises an Ig-like domain. Following the Ig domain is a type III fibronectin domain repeat, and IgSF is anchored to the membrane by the GPI moiety. This family is involved in homotypic or heterotypic binding and has the ability to bind to integrins or different IgSF CAMs.

Examples

• The neuronal cell adhesion molecule (NCAM), also known as CD56, is a homotypic glycoprotein expressed on the surface of neurons, glial cells and skeletal muscle. Although it is generally considered to be a marker of neurological lineage typing due to the site of discovery of CD56, expression of CD56 has also been found in hematopoietic systems and the like. Here, the expression of CD56 is most strictly related to natural killer cells, but is of course not limited thereto. CD56 has been detected on other lymphoid cells including dendritic cells including γ-δ (γδ) T cells and activated CD⁸⁺ T cells, as well as dendritic cells. NCAM is thought to play a role in cell adhesion, neurite outgrowth, synaptic plasticity, and learning and memory.

Figure 1. Structure of the NCAM1 protein.

• ICAM-1 (intercellular adhesion molecule 1), also known as CD54 (differentiation cluster 54), is a protein encoded by the ICAM1 gene in humans. This gene encodes a cell surface glycoprotein that is normally expressed on endothelial cells and cells of the immune system. It binds to CD11a/CD18 or CD11b/CD18 integrins and is used by rhinovirus as a receptor for entry into the respiratory epithelium.

Cadherin

Cadherin (called "calcium-dependent adhesion") is a cell adhesion molecule (CAM) that is important in forming adhesion junctions to bind cells to each other. Cadherin is a type 1 transmembrane protein. Their function depends on the calcium (Ca²⁺) ion, hence the name. Intercellular adhesion is mediated by the extracellular cadherin domain, while the intracellular cytoplasmic tail binds to many adaptors and signaling proteins, collectively known as cadherin colloids.

Figure 2. Ribbon representation of a repeating unit in the extracellular E-cadherin ectodomain of the mouse.

Integrin

Integrins are transmembrane receptors that promote cell-extracellular matrix (ECM) adhesion. After ligand binding, integrin activates signal transduction pathways that mediate cellular signaling, such as regulation of the cell cycle, organization of intracellular cytoskeleton, and movement of new receptors into the cell membrane. The presence of integrins allows for a rapid and flexible response to cell surface events such as signaling platelet priming and clotting factor interactions. There are many types of integrins, and the surface of one cell may have many different types. Integrins were found in all animals, while integrin-like receptors were found in plant cells. Integrins work in concert with other receptors such as cadherins, immunoglobulin superfamily cell adhesion molecules, selectins and synthetic polysaccharides to mediate cell-cell and cell-to-matrix interactions. Integrins include fibronectin, vitronectin, collagen and laminin.

Figure 3. Structure of the extracellular segment of integrin alpha Vbeta3.

C-type lectin receptors (CLR)

Many different cells of the innate immune system express numerous CLRs that shape innate immunity through their pattern recognition capabilities. Even though most types of human pathogens are covered by CLR, CLR is the primary receptor for identifying fungi: nevertheless, other PAMPs have been identified as targets for CLR in the study. Mannose is the recognition motif for many viruses, fungi and mycobacteria. Similarly, fucose has the same effect on certain bacteria and worms; dextran is present on mycobacteria and fungi. In addition, many acquired non-self-surfaces such as carcinoembryonic/carcinoembryonic new antigens with an "internal danger source" / "self-transformation to non-self" type of pathogen model can also be identified and destroyed by the immune system (eg by complement fixation or Other cytotoxic attack) or isolation (phagocytosis or phagocytosis). CLR. The name of the lectin is somewhat misleading because the family includes proteins with at least one C-type lectin domain (CTLD), a specific type of carbohydrate recognition domain. CTLD is a ligand binding motif found in more than 1000 known proteins (more than 100 in humans), which are usually not sugars. If the ligands are sugars, they require Ca²⁺ when they require sugar, hence the name "Type C", but many of them do not even have known glyco-ligands, so despite the folded structure with a lectin type, while some of them are not technically "lectins" in function.