Fig. 1.

A schematic depicting a generic non-proline α-amino acid (with linear side chain) and proline (with cyclic side chain). The amino acids are shown as part of a polypeptide chain where the main chain dihedral angles (ω, ϕ, and ψ) and the side chain dihedral angles (χ₁, χ₂, etc.) are shown in purple and red, respectively. Atoms of the preceding and following residues are shown in green, while the side chain atoms are boxed