Proline is amino-acid with special properties because it contains a side chain in which the R group on the α carbon is connected to the nitrogen (N). The covalent bond between the side-chain and the nitrogen has consequences on the properties of proline. Since there is no hydrogen attached to the nitrogen of a proline in a polypeptide chain, it limits proline capability to form main-chain hydrogen bonds. Also, the cyclic nature of proline imposes severe restrictions to the conformational freedom. There is a strict dependence between main- and side-chain proline conformations, so in proline, the trans isomer is only slightly favored over the cis isomer. Thus, proline can readily adopt the cis conformation.
Proline (Pro or P) is an amino acid that enters into the composition of proteins.
The structure of proline is a bit special since it is the only cyclic amino acid. Indeed, It has a side chain in which the R group on the alpha carbon is connected to the nitrogen. This arrangement makes it possible for proline to adopt backbone conformations that are not possible in other amino acids.
Its particular structure inserts a bend in the protein chains and breaks the α helices and the β sheets. It can, however, create particular helices, proline helices like those found in collagen.
Proline is a non-essential amino acid, synthesized by the body.
