What specific angle is crucial for β-turns to form correctly?

In the context of protein structure, β-turns, which are crucial for enabling polypeptide chains to change direction sharply, rely significantly on specific backbone dihedral angles known as phi (φ) and psi (ψ) angles. The arrangement of these angles allows for the proper folding of the protein and the formation of the characteristic turn structure.

Typically, in β-turns, the φ and ψ angles exhibit specific values that facilitate the compact folding necessary for the turn to occur. This compact conformation often includes hydrogen bonding between carbonyl oxygen and amide hydrogen across the turn, stabilizing the structure. Therefore, having the right phi-psi angles is essential for the correct spatial arrangement of residues in β-turns, making them pivotal for protein conformation and function.

While other angles such as the omega angle (which represents the rotation around the peptide bond and is usually considered as either cis or trans) and various bond angles are important for overall protein structure, it is the phi and psi angles that specifically dictate the formation of turns like the β-turn within polypeptide chains.