The major protein of connective tissue, cartilage and bone. Collagen has a unique triple helix configuration formed by three polypeptide subunits, known as alpha-chains. There are at least 16 types of collagen (up to 28 according to some authorities). The most common types are Type I, II, III, and IV. Type IV has fewer fibrils and forms the basement membrane.
Currently, there are over 22 different types of collagen identified, Type I to Type XXV, distributed in every organ and tissue of the body. The functional versatility of collagen is well documented from structural scaffolding for new tissue growth to possessing chemotactic properties that regulate cellular functions. There are seven collagen molecules that have recently been discovered but their function is still a mystery.
Key characteristics of the collagen types:
Location: Extracellular; skin, tendon, bone, teeth, scar tissue. Thick fibrils and fibers. Function: Strength and integrity of tissue, chemotactic for macrophage and fibroblast, adhesive properties, hydrophillic
Location: Extracellular; cartilage and vitreous humor. Thin fibrils. Function: Joint mobility and shock absorption.
Location: Extracellular; skin, muscle, blood vessels, lungs, granulation tissue. Intermediate-sized fibrils Function: Allows for distendibility and provides strength and integrity to tissue.
Location: Intracellular; basement membrane and lamina. Function: Component forming network Mesh-like scaffold for filtration.
Location: Extracellular; found in all tissue and around cells as a cytoskeleton. Function: Similar to Type III collagen.
Location: Generally found alongside type I.
Location: Epithelia (lining of GI tract, urinary tract, etc.).
Location: Lining of blood vessels. Type VIII collagen is a product of vascular smooth-muscle cells in development and disease. It is a short-chain collagen with considerable similarity to type X.
FACIT collagen, cartilage, assoc. with type II and XI fibrils. Collagen type IX contributes only 1% of the total collagen in mature articular cartilage. although it is present in much higher concentration in foetal cartilage.
Hypertrophic and mineralizing cartilage.
Location: Found alongside and interacts with types I and III. FACIT collagen, interacts with type I containing fibrils, decorin and glycosaminoglycans. Ligaments, tendons and tooth enamel.
Transmembrane collagen, interacts with integrin a1b1, fibronectin and components of basement membranes like nidogen and perlecan.