proliiniproline

Proline, also referred to as proliiniproline, is a non-essential amino acid. It is classified as a secondary amino acid due to its unique side chain structure. This structure consists of an imino group, which connects the alpha and gamma carbon atoms. As an imino acid, proline is able to form cyclic structures, setting it apart from other standard amino acids.

Proline plays a vital role in protein structure and function. Due to its cyclical side chain, proline is capable of forming hydrogen bonds between its carbonyl group and the amine group of an adjacent amino acid. This formation of hydrogen bonds structures, enhances protein stability, and contributes to protein folding. Proline is also a key participant in the formation of helical structures, known as polyproline II helices. These structures are often found in collagen and other proteins where they are essential for determining the protein's beta sheet conformation.

In peptides, proline is capable of restricting the adoption of alpha-helix structures due to the unique steric hindrance its imino side chain imparts. This is evidenced by polyproline II helices commonly found in collagen, Arabidopsis, and other polypeptides. Furthermore, the reduction of hydrophobic contacts due to the unique side chain also plays a role in peptide secondary structures.

Proline serves its biological functions in relatively small amounts within the body. A deficiency in proline can lead to disorders, including poor healing rates and skin problems. However, humans can synthesize proline from other amino acids such as glutamate through the action of enzymes called proline synthetase.