Collagen protein is part of the connective tissue of the body, helping to support various tissues and organs. As such, it forms part of the bones, cartilage and skin. There are many types of collagen, and they form various structures and perform different functions. Mutations in this protein can lead to numerous diseases.
Connective Tissue and Collagen
The connective tissue supports the tissues and organs of the body, and includes the bones, skin, blood vessels, lymphoid tissue and cartilage. Collagen protein makes up some of the structures of the connective tissue and forms such a large part of it, that approximately 25 percent of the protein in the body is collagen, according to Robert Murray, M.D., Ph.D., emeritus professor of biochemistry at the University of Toronto, in "Harper's Illustrated Biochemistry." There are at least 28 kinds of collagen.
Collagen Structure
Collagen protein forms various structures, as described by Anthony Mescher, Ph.D., professor of anatomy and cell biology at the Indiana University School of Medicine, in "Junqueira's Basic Histology." Some types of collagen group together to form structures called fibrils, which are thin, long fibers. Others form short structures that hold the fibrils to each other. Some act like anchors, while others form a network. They are made by different types of cells including fibroblasts, osteoblasts and keratinocytes. Fibroblasts make collagen, while osteoblasts make bone and the keratinocytes are skin cells.
Collagen Proteins in the Skin
Most of the collagen in the body is collagen type I. It is found in the tendons and the bones, and makes up approximately 80 percent of all of the collagen in the skin, according to Jouni Uitto, M.D., Ph.D., chair of the department of dermatology and cutaneous biology at Thomas Jefferson University, in "Fitzpatrick's Dermatology in General Medicine." Because of its structure, the skin has protection against many forms of trauma. Collagen type III is 10 percent of all of the collagen in the skin, while type V is 5 percent.
Other Common Types
Collagen type II is another type of collagen and it is found in hyaline cartilage. In addition to forming part of the skin, collagen type III is found in the blood vessels, stomach and intestines. Uitto writes that type IV is very abundant in the basement membrane. This membrane is a structure that separates the connective tissue from the epithelium, or the cells that line various structures in the body.
Mutations in Collagen
The importance of the collagen protein is demonstrated by the fact that mutations in collagen can cause disease. A mutation in collagen types I or III can lead to Ehlers-Danlos syndrome. People with this disease have abnormally flexible joints, very stretchable skin and fragile blood vessels, writes Frank Pessler, M.D., Ph.D., pediatric rheumatologist at the Technical University of Dresden, in "The Merck Manual for Healthcare Professionals." Abnormalities in type IV can cause Alport's syndrome, where males have problems in the basement membrane of their kidneys that usually result in renal failure.
References
- "Fitzpatrick's Dermatology in General Medicine"; Klauss Wolff, M.D., Lowell Goldsmith, M.D. et al.; 2008
- "Harper's Illustrated Biochemistry"; Robert Murray, M.D., Ph.D., David Bender, Ph.D., Kathleen Botham, Ph.D. et al.; 2009
- "Junqueira's Basic Histology: Text & Atlas"; Anthony Mescher, Ph.D.; 2010
- The Merck Manual for Healthcare Professionals: Ehlers-Danlos Syndrome
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