What is the Difference Between Fibronectin and Laminin

The main difference between fibronectin and laminin is that the fibronectin is a glycoprotein found in the extracellular matrix (ECM) and in the blood plasma whereas laminin is a glycoprotein, which serves as the main component of the basal lamina. Furthermore, fibronectin is essential in wound healing while laminin is vital in the neural development and peripheral nerve repair.

Fibronectin and laminin are two types of high-molecular-weight glycoproteins found in the ECM. Both types of proteins are crucial in cell adhesion, migration, growth, and differentiation.

Key Areas Covered

1. What is Fibronectin
     – Definition, Structure, Function
2. What is Laminin
     – Definition, Structure, Function
3. What are the Similarities Between Fibronectin and Laminin
     – Outline of Common Features
4. What is the Difference Between Fibronectin and Laminin
     – Comparison of Key Differences

Key Terms

Basal Lamina, Cell Adhesion, CIg, Extracellular Matrix (ECM), Fibronectin, Glycoproteins, Integrins, Laminin

What is Fibronectin

Fibronectin is a high-molecular-weight (~440kDa) glycoprotein that occurs in the extracellular matrix. It binds to integrins, a type of membrane-spanning receptor proteins. In addition, it can bind to the components of the ECM such as collagen, fibrin, and proteoglycans. Also, fibronectin in the ECM is insoluble, and primarily, fibroblasts secrete this glycoprotein.
Moreover, a soluble form of fibronectin occurs in the blood plasma. It is formally called the “cold-insoluble globulin”, or CIg. Hepatocytes of the liver produce CIg. The CIg is one of the major protein in the plasma, and its concentration is 300 μg/ml.

Figure 1: Extracellular Matrix Components of Cartilage

Furthermore, fibronectin has two subunits that vary in size (235-270 kDa) as a result of alternative splicing. The secreted or the soluble fibronectin polymerizes to higher order fibrils that are insoluble and occur in the ECM.

Functionally, fibronectin is responsible for cell adhesion, growth, migration, and differentiation. In addition, it is vital in actin dynamics, wound healing, and embryonic development. The binding of the fibronectin to integrins mediate the function of fibronectin. Besides, altered fibronectin biochemistry associates with a number of consequential pathologies including fibrosis and cancer.

What is Laminin

Laminin is another high-molecular-weight glycoprotein that occurs in the ECM. It is a major component of the basal lamina, which is one of the layers of the basement membrane.

Furthermore, laminin is a heterotrimer that contains an α-, a β-, and a γ-chain. Moreover, the basis of classification of laminin is their chain composition. Around fifteen different chain combinations occur in vivo.

Functionally, laminin is important in the cell adhesion, differentiation, and migration. In addition, laminin has a role in the neurite outgrowth and regeneration. Same as fibronectins, integrins mediate the function of most laminins.

Figure 2: Laminin 111

Meanwhile, defective laminins can cause muscular dystrophy, defects of the kidney filter (nephrotic syndrome), and lethal skin blistering disease (junctional epidermolysis bullosa).

Similarities Between Fibronectin and Laminin

• Fibronectin and laminin are two types of high-molecular-weight glycoproteins in the ECM.
• They are fibrous proteins.
• Moreover, these proteins are important in cell adhesion, growth, migration, and differentiation.
• Furthermore, integrin surface receptors mediate the function of both types of proteins.

Difference Between Fibronectin and Laminin

Definition

Fibronectin refers to a fibrous protein that binds to collagen, fibrin, and other proteins and also to the cell membranes, functioning as an anchor and connector. Whereas, laminin refers to a fibrous protein present in the basal lamina of the epithelia. Therefore, these definitions explain the main difference between fibronectin and laminin.

Molecular Weight

The molecular weight of fibronectin is ~440 kDa while the molecular weight of laminin is 400-900 kDa.

Structure

Another difference between fibronectin and laminin is that the fibronectin is a homodimer while the laminin is a heterotrimer.

Location

An important difference between fibronectin and laminin is the place of occurence. While fibronectin occurs in the ECM and bloodstream, laminin mainly occurs in the basal lamina.

Functional Significance

Moreover, fibronectin is important in wound healing while laminin is important in the development of neurons and peripheral nerve repair. Thus, this is another difference between fibronectin and laminin.

Disorders

Besides, a defective fibronectin can cause cancer and fibrosis while defective laminin can cause muscular dystrophy, defects of the kidney filter, and lethal skin blistering disease.

Conclusion

Fibronectin is a high-molecular-weight glycoprotein mainly found in the ECM, attached to the integrins. The soluble part of the fibronectin occurs in the blood plasma. Laminin is another high-molecular-weight glycoprotein that occurs in the ECM and is a major component of the basal lamina. The primary function of fibronectin and laminin is to aid in cell adhesion, growth, differentiation, and migration. Fibronectin helps in wound healing while laminin helps in the neural development and peripheral nerve repair. Thus, the main difference between fibronectin and laminin is the structure and differential functions.

References:

1. Carlsson, R et al. “Laminin and fibronectin in cell adhesion: enhanced adhesion of cells from regenerating liver to laminin” Proceedings of the National Academy of Sciences of the United States of America vol. 78,4 (1981): 2403-6. Available Here

Image Courtesy:

1. “Extracellular Matrix Components of Cartilage” By Kassidy Veasaw – Own work (CC BY-SA 4.0) via Commons Wikimedia  
2. “Schematic Diagram of Laminin 111” By Maiaaspe – Own work (CC BY-SA 3.0) via Commons Wikimedia