Proline

Proline is a non-essential amino acid that is involved in the production of collagen and in wound healing. Proline is actually not an amino acid, but an imino acid. The primary amine on the α carbon of glutamate semialdehyde forms a Schiff base with the aldehyde which is then reduced, yielding proline. Unlike other amino acids which exist almost exclusively in the trans- form in polypeptides, proline can exist in the cis-configuration in peptides. When proline is in a peptide bond, it does not have a hydrogen on the α amino group, so it cannot donate a hydrogen bond to stabilize an α helix or a β sheet.

Proline is unable to occupy many of the main chain conformations easily adopted by all other amino acids. Proline is unique in that it is the only amino acid where the side chain is connected to the protein backbone twice, forming a five-membered nitrogen-containing ring. Proline is a component of collagen, a major structural component of cells and animals. Collagen, which is the most abundant protein in the body, makes up much of the organic mass of skin, tendon, blood vessels, bone, cornea, vitreous humor of the eye, and basement membranes of all organs. Collagen is composed of the metabolic by-product of proline called hydroxyproline.

Proline functions, uses, and health benefits

Proline is the precursor for hydroxyproline, which the body incorporates into collagen, tendons, ligaments, and the heart muscle. Proline helps strengthen cardiac muscle. Collagen in the skin contains hydroxyproline and hydroxylysine, which is formed from proline and lysine, in which ascorbic acid (vitamin C) seems to be important in this conversion. Collagen contains about 15 % proline. It also helps in the maintenance and healing of cartilage and the strengthening of joints, tendons, and muscles including the heart muscle. The metabolism of proline is connected to enzymes that require niacin and vitamin C. Proline is an important component in certain medical wound dressings that use collagen fragments to stimulate wound healing.

Osteoarthritis may be related to abnormalities in collagen structure as well as the bone disease, osteogenesis imperfecta. Proline improves skin texture by aiding in the production of collagen and reducing the loss of collagen through the aging process. Proline plays important roles in molecular recognition, particularly in intracellular signalling. Domains such as WW and SH3 bind to specific proline containing peptides that are key parts of many signalling cascades. SH3 (Src homology region 3) and WW domains of signal transduction pathway proteins recognize proline containing sequences and are used to mediate protein-protein interactions of signal transduction components.

Dietary sources of proline

Proline is a nonessential amino acid, which means that it is manufactured from other amino acids in the liver. Proline is found in most protein sources, primarily from animal products such as dairy products, eggs, beef and poultry.