Proline is one of the 20 amino acids that build proteins. It is unique due to its cyclic structure, where its side chain loops back and bonds to its own backbone nitrogen atom. This forms a rigid five-membered ring, making its alpha-amino group a secondary amine, unlike the primary amine found in most other amino acids. This arrangement gives proline unique rigidity, which influences the shape and stability of the proteins it becomes a part of.
Proline’s Function in the Body
Proline plays an important role in the body, particularly in the synthesis and structural integrity of collagen. Collagen is the body’s most abundant protein, providing structure, strength, and support to various tissues. It is a primary component of skin, bones, tendons, ligaments, cartilage, organs, and blood vessels.
Proline, along with glycine and hydroxyproline, are key amino acids that form collagen’s triple-helix structure. Proline residues are often hydroxylated to form hydroxyproline, a modification important for stabilizing this triple helix. Without adequate hydroxylation, collagen chains cannot fold into stable triple helical molecules at body temperature. This structural stability is achieved through hydrogen bonds and chemical crosslinks that fortify collagen’s structure, ensuring tissue robustness.
Beyond its direct role in collagen, proline’s unique cyclic structure influences broader protein folding processes. Its rigidity can introduce turns and kinks in protein structures, which are necessary for a protein to achieve its proper three-dimensional shape and function. While it can be an “alpha-helix breaker” due to its restricted rotation, it is also commonly found at the beginning of alpha helices and in beta sheets, contributing to the precise folding of proteins.
Natural Sources of Proline
The human body can synthesize proline, classifying it as a non-essential amino acid. It can also be obtained through diet, particularly from protein-rich foods. Animal products are sources of proline, including meats, poultry, fish, eggs, and dairy.
Collagen-rich foods, such as bone broth, are high in proline. Plant-based sources include soy, legumes, and cabbage. Since the body produces proline from compounds like glutamic acid, deficiencies are uncommon with adequate protein intake.
Proline as a Supplement
As a non-essential amino acid, the body generally produces enough proline for its needs through biochemical processes. However, proline can become “conditionally essential” during periods of heightened demand, such as significant physical stress, injury, or illness, where the body’s natural production may not meet the increased requirements. For example, in wound healing, proline-rich collagen can support tissue repair and wound closure.
People may consider proline supplementation, often in forms like L-proline powder or capsules, to support specific health goals. This might include supporting joint health or aiding in skin repair, given proline’s foundational role in collagen synthesis. While research continues, these supplements are often explored for their potential to provide additional building blocks when the body’s demands for collagen synthesis are elevated.