Laminin is a large, cross-shaped glycoprotein that is a critical component of the basement membrane, a specialized layer of the extracellular matrix (ECM) that supports and organizes cells, especially in epithelial and endothelial tissues.
Definition:
Laminin is a multi-domain adhesive protein that connects cells to the basement membrane, influencing cell adhesion, migration, differentiation, growth, and tissue organization.
Structure:
- Laminin is a heterotrimer, made of three different polypeptide chains:
- α (alpha)
- β (beta)
- γ (gamma)
- These chains form a cross-shaped structure, with the long arm made by all three chains and three short arms each composed of one chain.
- There are multiple isoforms of each chain, giving rise to many laminin isoforms (e.g., laminin-111, laminin-511).
Functions of Laminin:
- Cell adhesion: Binds to cell surface receptors like integrins and dystroglycan, anchoring cells to the basement membrane.
- Basement membrane assembly: Helps form the structural scaffold that supports tissues like skin, muscle, and nerves.
- Cell signaling: Influences cellular behavior including polarity, proliferation, and apoptosis.
- Tissue stability and regeneration: Critical in nerve regeneration, muscle stability, and epithelial tissue integrity.
Where Laminin Is Found:
- Basement membranes beneath:
- Epithelial cells (e.g., skin, gut lining)
- Endothelial cells (lining blood vessels)
- Muscle fibers
- Nerve cells (Schwann cell basement membranes)
- Embryonic tissues, where it guides development
How It Works:
- Laminin self-assembles into networks that link to other ECM proteins such as collagen IV and nidogen/entactin.
- These networks form a stable scaffold.
- Laminin interacts with receptors on cells, transmitting mechanical and chemical signals.
Laminin vs. Other ECM Proteins:
| Protein | Main Role | Found In |
|---|---|---|
| Laminin | Cell adhesion and guidance | Basement membrane |
| Collagen IV | Structural support | Basement membrane |
| Fibronectin | Wound healing and adhesion | Connective tissue, plasma |
| Elastin | Tissue elasticity | Arteries, skin, lungs |
Clinical Significance:
- Congenital defects: Mutations in laminin genes (e.g., LAMA2) can lead to muscular dystrophies and skin blistering diseases.
- Cancer: Laminin expression patterns can influence tumor invasion and metastasis.
- Nerve regeneration: Laminin supports axon growth and is used in regenerative medicine scaffolds.
Summary:
| Feature | Description |
|---|---|
| Structure | Heterotrimer of α, β, γ chains in a cross shape |
| Main Location | Basement membrane |
| Major Functions | Cell adhesion, basement membrane assembly, tissue integrity |
| Binds To | Integrins, collagen IV, nidogen, dystroglycan |
| Clinical Relevance | Development, tissue repair, congenital diseases, cancer |