Proteoglycans complex macromolecules made up of a core protein covalently attached to one or more glycosaminoglycan (GAG) chains . They are major components of the extracellular matrix (ECM) structural support , cell signalinghydration , and tissue resilience .
Structure:
Core protein : The central protein backbone.GAG chains : Long, linear carbohydrate chains that are negatively charged and hydrophilic. Common GAGs include:
Chondroitin sulfate Heparan sulfate Dermatan sulfate Keratan sulfate Hyaluronic acid (though this one is technically not covalently attached to a protein)
Together, these components make proteoglycans highly water -absorbent , contributing to the gel-like nature of connective tissues.
Function:
Structural support : Provide compressive strength to cartilage , skin , and joints (e.g., aggrecan in cartilage).Hydration : GAGs attract water, keeping tissues moist and cushioning joints.Cell signaling : Bind and regulate the availability of growth factors (e.g., heparan sulfate proteoglycans modulate FGFs).Barrier function : In epithelial tissues, proteoglycans help maintain selective permeability.Tissue development and repair : Regulate cell migration, proliferation, and differentiation during development and healing.
Examples of Proteoglycans: Proteoglycan Location / Function Aggrecan Cartilage; provides shock absorption and water retention Decorin Connective tissues; regulates collagen fibril formation Perlecan Basement membranes; involved in filtration and cell signaling Versican Found in many tissues; involved in cell adhesion and migration Syndecan Cell surface; interacts with the cytoskeleton and signaling molecules
Proteoglycans vs. Glycoproteins: Feature Proteoglycans Glycoproteins Sugar content Mostly carbohydrates (up to 95%) Smaller carbohydrate portion Structure Core protein + long GAG chains Protein + short branched oligosaccharides Function Structural, signaling, hydration Signaling, enzymatic, immune-related
Clinical Relevance:
Osteoarthritis : Breakdown of aggrecan reduces cartilage cushioning.Cancer metastasis .Congenital disorders : Mutations in proteoglycan-related genes can lead to skeletal and connective tissue diseases.Tissue engineering : Used in scaffolds to mimic the natural ECM for regenerative medicine .
Summary Table: Property Description Type Glycoprotein with long GAG chains Location Extracellular matrix, cell surfaces Functions Support, hydration, signaling, barrier Examples Aggrecan, decorin, perlecan, syndecan Clinical Importance Arthritis, cancer, developmental disorders
