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Extracellular Matrix Proteins

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The extracellular matrix can be understood as a suspension of macromolecules that aids in the maintenance of a complete organ as well as local tissue growth. All of these chemicals were secreted by nearby cells. The proteins will undergo scaffolding after being secreted. The transitory structures that form between individual proteins to create more complex protein polymers are known as scaffolding. The matrix will become viscous due to these stiff, albeit transient, protein structures.

A cell is surrounded by the extracellular matrix, a mesh structure consisting of water, various proteins, and carbohydrates. It aids in cell motility, intercellular adhesion, and communication, as well as cell support within a tissue.

Most cells create substances and materials that are intended to be secreted in the cell’s extracellular environment (extracellular space). These substances combine to create an extracellular matrix (ECM), which surrounds the cell and performs structural and intercellular interaction tasks. The extracellular matrix is a three-dimensional network made up of extracellular macromolecules and minerals like collagen, enzymes, glycoproteins, and hydroxyapatite that support the surrounding cell’s structural and biochemical needs. The composition of the extracellular matrix (ECM) differs throughout multicellular structures because multicellularity originated independently in several multicellular lineages; nonetheless, cell adhesion, cell-to-cell communication, and differentiation are primary functions of the ECM.

Structure of Extracellular Matrix

 

The ECM is primarily made of water and a variety of proteins and carbohydrates, and the amount of each component varies depending on the type of tissue. The brain and cardiac muscle are two examples of tissues that are predominantly made up of cells with some ECM in between, whereas other tissues, referred to as connective tissues, are primarily made up of ECM with a few scattered cells suspended inside them. Resident cells create ECM components intracellularly and secrete them into the ECM. After being secreted, they combine with the present matrix. A network of fibrous proteins and glycosaminoglycans make up the ECM.

Protein Components in Extracellular Matrix

The main components of an animal’s ECM include water, proteins, and polysaccharides. The unique texture (ranging from liquid and gel-like to solid) and structure and function of tissue is determined by variations in the organization of these molecules and their relative amounts. The main elements of ECMs are described in the following sections.

Structural Proteins

The main structural proteins of the extracellular matrix that help to produce fibers are:

  • Collagen 
  • Elastin

Collagen is a protein that makes up a significant portion of the extracellular matrix. When collagen proteins are released from the cell, they assemble into long fibers known as collagen fibrils after being modified with carbs. Collagen is essential for the strength and structural integrity of tissues. Fragile tissues that stretch and tear too easily are a result of human genetic illnesses that alter collagen, such as Ehlers-Danlos syndrome.

The glycoprotein collagen makes up the majority of the extracellular matrix in animal cells. Proteins with carbohydrates linked to them are called glycoproteins. Collagen molecules emerge from the cell in long fibers known as collagen fibrils. There are many different forms of collagen since it is so prevalent in animals—it makes up about 30% of their proteins. A tissue’s collagen fibers are a mixture of many types, with one form of collagen often predominating over others depending on the tissue’s needs. Depending on the tissue, the collagen fibrils arrange themselves differently.

Elastin is a glycoprotein that is commonly found in ECM, that binds with collagen. Elastin creates extensible elastic fibers that give tissues subjected to repeated stretching flexibility. Lung tissues and the vasculature (circulatory system) are two tissues with significant elastin content. This is important for the lungs, skin, ligamentum nuchae, blood vessels, and other tissues that have high elastin content. Fibroblasts and smooth muscle cells produce elastin. Tissues that need to be both firm and elastic contain elastin (skin, blood vessels, lungs). In arteries, it is the major protein.

Proteoglycan

Proteoglycan complexes form a net into which collagen fibers are incorporated. The complexes are made up of hundreds of proteoglycan molecules along a lengthy polysaccharide (carbohydrate) chain. Collagen fibers and a family of proteoglycans that contain carbohydrates are woven together in the extracellular matrix. These proteoglycans may be connected to lengthy polysaccharide backbones. The GAG chains in the proteoglycan complexes have a high water absorption capacity, which contributes to some connective tissues’ gel-like consistency. The matrix can withstand compressive stresses it.

Adhesion Protein

Various adhesive fibrous glycoproteins that bind to both cells and other matrix macromolecules are present in the extracellular matrix and help the cells attach to it. the extracellular matrix’s best-characterized large adhesive glycoproteins are,

  • Fibronectins 
  • Lamina

Fibronectins are other receptor glycoproteins, that connect the ECM to the cell membrane’s outside. The integrins, which are embedded in the plasma membrane, are what the fibronectins bind to. The integrins cover the entire breadth of the plasma membrane, and their cytoplasmic side interacts with microfilament-bound proteins to form bonds (elements of the cell cytoskeleton). These glycoproteins thereby support cell attachment to the ECM. 

Fibronectins are composed of two similar but distinct polypeptide chains. Near the carboxyl terminus, two disulfide bonds bind the two polypeptides together. Each chain is folded into a set of flexible polypeptide segments that connect a series of globular domains. The cells that are surrounded by the extracellular matrix are in close contact with one another. Integrins, a class of proteins found embedded in the plasma membrane, are some of the crucial connectors. Integrins and other extracellular matrix proteins like collagen can communicate with one another through extracellular matrix proteins like fibronectin molecules. Integrins and the cytoskeleton are connected on the inner side of the membrane.

Lamina is a sticky glycoprotein. Epithelial cells specifically secrete it. All basal laminae contain a significant portion of this protein. It connects type IV collagen of the basal lamina to the epithelial cells. It has a very odd asymmetric cross-shaped structure with an extended long arm ending with a big domain at one pole and three short arms containing two globular domains in each arm at the other end.

The extracellular matrix protein laminin is the first to develop in the embryo. It serves as a significant filtration barrier in the kidney. Antibodies are created against laminin when this protein accumulates in the glomerular basement membrane, significantly impairing kidney function. Diabetes patients’ basement neurons have more laminin. Additionally, antibodies are present in Chagas disease.

Functions of Extracellular Matrix

  • The ECM controls intercellular adhesion and communication as well as a mechanical support for the tissue’s cells. The ECM is vitally important and highly dynamic, according to a recent study. It decides and regulates crucial cell behaviors and traits such as division, adhesion, migration, polarity, differentiation, and apoptosis. 
  • The extracellular matrix is important for processes including growth, wound healing, and fibrosis. Important effects on cell motility, gene expression, and differentiation are caused by the ECM’s stiffness and elasticity.
  • The ECM’s strong collagen fibers primarily provide mechanical support for tissues. Furthermore, a proteoglycan’s carbohydrate chains are excellent at absorbing water, and the amount of water varies depending on the tissue, giving the matrix a hydrated gel consistency. Because of its gel-like consistency, the ECM also helps to withstand compressive stresses.

Clinical Significance of Extracellular Matrix

It has been discovered that the extracellular matrix promotes tissue repair and renewal. MBVs, or matrix-bound nanovesicles, are important participants in the healing process. All portions of the human body can grow and regenerate in developing human fetuses due to the extracellular matrix and stem cells, and they can repair any damage they sustain in the womb. It has previously been used to assist horses in healing injured ligaments, but it is currently being studied as a tool for human tissue regeneration.

The extracellular matrix has two primary functions in tissue engineering and damage repair. It first stops the immune system from being activated by the damage and produces inflammation and scar tissue as a reaction. Then, rather than causing scar tissue to grow, it helps the nearby cells to repair the tissue. In vitro differentiation of epithelial, endothelial, and smooth muscle cells is induced by extracellular matrix proteins, which are frequently used in cell culture systems to retain stem and progenitor cells in undifferentiated conditions. Proteins from the extracellular matrix can also enable 3D cell culture in vitro for the purpose of simulating the development of tumors.

FAQs on Extracellular Matrix Protein

Q1: What are Proteoglycans?

Answer: 

Proteoglycans are a molecular class different from fibrous proteins and have unique properties. Proteoglycans, unlike fibrous proteins, will not provide cells with their distinctive stretch resistance and will instead have a protein core with surrounding sugar groups.

Q2: What are the main functions of the Extracellular Matrix?

Answer: 

The Extracellular Matrix can perform a variety of functions, including controlling intercellular communication, separating tissues from one another, and providing support. The dynamic behavior of a cell is regulated by the extracellular matrix.

Q3: What is the role of collagen in the Extracellular Matrix?

Answer:

The glycoprotein collagen, which is also the most common protein in animals, is the most prominent element of the Extracellular Matrix. Collagen fibers in an Extracellular Matrix primarily sustain the tissue’s cells by acting as structural support.

Q4: What are the main connectors in the Extracellular Matrix?

Answer: 

Integrins, a class of proteins found embedded in the plasma membrane, are some of the major connectors. fibronectin molecules, which are extracellular matrix proteins, can serve as a bridge between integrins and other extracellular matrix proteins like collagen.



Last Updated : 13 Jan, 2024
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