11. Which of the following is NOT a cell adhesion protein?
    Question
    (1) Cadherin
    (2) Selectin
    (3) Immunoglobulin (lg) superfamily
    (4) Laminin

Introduction: What Are Cell Adhesion Proteins?

Cell adhesion proteins, or cell adhesion molecules (CAMs), are glycoproteins expressed on cell surfaces to help cells stick together and interact with the extracellular matrix. CAMs play vital roles in multicellular tissue formation, signaling, and immune function. They are classified into major families based on structure and binding properties.​

CAM Families: Cadherin, Selectin, and Ig Superfamily

Cadherin

Cadherins are calcium-dependent CAMs that enable strong, specific cell-cell adhesion, crucial for tissue integrity and adherens junctions.​

Selectin

Selectins are CAMs involved in transient cell-cell interactions, especially during immune responses and lymphocyte homing. They bind carbohydrate groups on other cell surfaces.​

Immunoglobulin Superfamily (IgSF CAMs)

The immunoglobulin superfamily CAMs are the most diverse cell adhesion family, mediating both homophilic and heterophilic cell-cell binding via Ig-like domains.​

Why Laminin Is Not a Cell Adhesion Protein

Laminin is a high molecular weight glycoprotein found in the extracellular matrix, particularly abundant in the basal lamina. Laminin acts mostly as a ligand for cell adhesion proteins (like integrins) and scaffolds for tissue architecture; it does not directly mediate cell-cell or cell-matrix adhesion as a CAM.​

• Laminin provides structural support and organizes the ECM but does not act as a cell surface adhesion receptor.​

• Cell adhesion relies on CAMs binding to laminin, not vice versa.

Comparison Table

Conclusion

• Cadherin, selectin, and Ig superfamily proteins are all bona fide cell adhesion molecules.

• Laminin, while essential for matrix structure and cell anchoring, is NOT classified as a cell adhesion protein; it acts as an ECM scaffold and ligand for CAMs.​

• Knowing these distinctions is fundamental in cell biology, tissue engineering, and medical science regarding adhesion and extracellular matrix organization.