13. Which one of the following proteins is NOT related to extracellular matrix?
    (1) Cadherin (2) Vitronectin
    (3) Lamin (4) Selectin

Introduction: The Extracellular Matrix Defined

The extracellular matrix (ECM) is an intricate network of macromolecules—proteins and carbohydrates—providing structural support, organization, and regulatory signals for cells in animal tissues. Prominent ECM proteins include collagen, elastin, laminin, vitronectin, and fibronectin, which serve as the physical scaffolding and environment for cells.​

ECM Proteins: Vitronectin and Laminin

Vitronectin

Vitronectin is a multifunctional glycoprotein found abundantly in the ECM. It binds integrins and supports cell adhesion, spreading, migration, and tissue remodeling. Vitronectin also regulates certain protease activities and participates in wound healing and angiogenesis.​

Laminin

Laminin (not “lamin,” which is a nuclear lamina protein; here, “lamin” is likely referring to ECM laminin) forms networks in the basement membrane, binding cells through various integrins and supporting tissue structure, cell polarity, and differentiation.​

Cadherin: A Cell Adhesion Molecule

Cadherins are transmembrane glycoproteins that mediate calcium-dependent cell-cell adhesion and play a key role in maintaining tissue integrity and communication. They do not function as ECM components; rather, they connect adjacent cells at adherens junctions and desmosomes.​

Selectin: Cell-Cell Adhesion, Not ECM

Selectins are a family of cell adhesion molecules that bind specific carbohydrate groups on other cell surfaces, primarily mediating transient interactions during inflammatory responses. While not an ECM protein, selectins contribute to immune cell movement.​

Comparison Table

Conclusion

• Cadherin is NOT related to the extracellular matrix but is a cell adhesion molecule enabling direct cell-cell interaction.​

• Vitronectin and laminin are fundamental ECM proteins providing structural and adhesive support for cells in tissues.​

• Selectin, like cadherin, is primarily a cell adhesion molecule and not part of the ECM scaffold.​

• This distinction is essential for understanding tissue organization, repair, and cellular communication.