In protein folding, what role does proline typically play in β-turns?

Proline plays a unique and crucial role in protein structure, particularly in the formation of β-turns. In a β-turn, proline can induce bends in the polypeptide chain due to its distinctive cyclic structure. The rigid ring structure of proline restricts the rotation around the N-Cα bond, leading to a less flexible backbone. This characteristic allows proline to effectively change the direction of the polypeptide chain, which is essential for the tight turns that occur in protein structures.

β-turns are important as they facilitate the compact folding of proteins and are often found in the loops connecting strands of β-sheets. By introducing these bends, proline helps stabilize the overall three-dimensional structure of the protein, allowing for proper function and interaction with other molecules.

While proline does not stabilize α-helices, contribute significantly to hydrophobic interactions, or directly form hydrogen bonds like other amino acids, its key ability to induce bends in the polypeptide chain makes it critical in the formation of these structural motifs in proteins.