Collagen vs Elastin
Connective tissues are important for binding and connecting other tissues within the body. They also provide strength, support, and shape to the tissues. The connective tissue is a system in which cells are scattered throughout an extracellular matrix. In addition to cells, the insoluble protein fibers are also embedded in the matrix. The matrix is called the ground substance. These tissues are widely distributed in the body, matrix bone, tendons and ligaments, and cartilage. The connective tissues consist of four basic tissues, collagen, elastin, proteoglycans, and glycoproteins.
Collagen
Collagen is the most abundant protein found in connective tissues. It provides great tensile strength and holds cells together. In addition, it helps to align the cells, thus allows in proliferation and differentiation of cells. Tropocollagen is the basic structural unit of collagen that consists of α- chains. Each α-chain is made up of three polypeptide chains twisting around each other in a triple helix to form a rope like structure. There are hydrogen bonds between the polypeptide chains to hold them tightly. Each of this polypeptide chain has equal length and contains about 1000 amino acids residues. Various triple helical combinations of polypeptides in α-chains result multiple types of collagen in humans connecting tissues (19 types of collagen have been identified so far). Most abundant types of collagen are distributed in skin, tendon, bone, comea, articular cartilage, intervertebral disk, fetal skin, cardiovascular system, placenta etc. The cross-links are important to provide a high tensile strength in collagen. There are three types of inter or intramolecular cross-links involved to stabilize the collagen fibers; they are aldol condensation, Schiff base, and lysinonorleucine.
Elastin
Elastin is made up of basic subunit called tropoelastin, which contains about 800 amino acid residues. The cross-links of elastin are more complex than that of collagens. Desmosine is the major type of cross-links found in elastin. They are formed from the condensation of the allysine residues with lysine. Elastin often occurs with collagen in connective tissues. It is a rubber-like protein so that it can stretch up to several times their length and return back to their original shape and length when the tension is released. Due to this property, it is largely found in the tissues associated with lungs, blood vessels and ligaments, which undergo large expansions. In addition, they are also found in places like skin, ear cartilage and several other tissues in small quantities.
What is the difference between Collagen and Elastin?
• There is only one genetic type of elastin, whereas there are many different genetic types of collagen.
• Elastin has enough capacity to stretch and subsequently to recoil while collagen has no such capacity to stretch.
• Collagen’s primary structure has repeating (Gly-X-Y) sequences whereas, in elastin, there are no such repeating (Gly-X-Y) sequences.
• In contrast to collagen, there is no formation of triple helix in elastin.
• Hydroxylysine is present in collagen, whereas it is absent in elastin.
• Glycosylated hydroxylysine is present in collagen, whereas it is absent in elastin.
• The major cross-links formed in collagen are intramolecular aldol cross-links, whereas those in elastin are intramolecular desmosine cross-links.