17. Integrin molecule link extracellular matrix (ECM) to the actin cytoskeleton of cell. Integrin binds to which of the following ECM macromolecules?
    (1) Laminin (2) Collagen
    (3) Fibronectin (4) Vitronectin

Integrins are transmembrane receptors that directly bind to several key extracellular matrix (ECM) macromolecules, forming physical links from the ECM to the actin cytoskeleton within the cell. The major ECM proteins that serve as ligands for integrins include laminin, collagen, fibronectin, and vitronectin. Each type of integrin (defined by specific alpha and beta subunits) exhibits binding affinity for one or more of these ECM proteins, facilitating vital roles in cell adhesion, signaling, and tissue integrity.

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Introduction: Integrin as an ECM Receptor

Integrins are the central transmembrane receptors that form strong, specific attachments between the cell’s cytoskeleton and ECM macromolecules. This relationship is critical for cell migration, tissue strength, and signaling events that regulate growth, repair, and differentiation.

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Integrin Binding to ECM Proteins

Laminin

Integrins such as α6β1 and α6β4 specifically bind to laminin, a key structural protein of the basal lamina responsible for cell-matrix adhesion and tissue organization.

Collagen

Integrins containing α1β1 and α2β1 subunits preferentially bind collagen, providing structural rigidity and enabling mechanical support within connective tissues.

Fibronectin

Integrin α5β1 interacts robustly with fibronectin, supporting cell adhesion, migration, and the formation of focal adhesions critical for tissue repair and morphogenesis.

Vitronectin

Vitronectin, another ECM glycoprotein, binds integrins such as αVβ3, enhancing cell adhesion and signaling, especially within processes like wound healing and tissue remodeling.

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Table: Integrin-ECM Binding

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Conclusion

• Integrins can bind directly to laminin, collagen, fibronectin, and vitronectin—making them essential receptors for anchoring cells to the extracellular matrix and integrating signals from outside to inside the cell.

• This multi-protein interaction is central to tissue organization, cell movement, and robust signaling pathways vital for health and disease.