Which amino acid is commonly found at position 2 in beta turns?

In the context of protein structure, beta turns are specific structural motifs that facilitate the change in direction of the polypeptide chain. Position 2 of a beta turn is particularly important for the turn's stability and conformation. Proline is frequently found at this position due to its unique cyclic structure, which introduces a rigid bend in the peptide chain.

Proline's five-membered ring restricts the flexibility of the backbone, which is beneficial in the tight geometry of a beta turn. By contributing to the turn’s spatial arrangement, proline helps maintain the compactness and overall shape of the protein. Its presence at this position is not merely a preference but is often crucial for facilitating the structural integrity of the turn.

In contrast, while glycine, serine, and alanine can also participate in beta turns, they do not impart the same degree of rigidity as proline does. Glycine, for instance, offers flexibility but lacks the structural constraints that help stabilize the tight turn. Thus, while other amino acids may appear in beta turns, proline's specific characteristics make it the most commonly found at position 2.