Fig 6. Average values of Φ (Phi) and Ψ (Psi) torsion angles of helical residues in PDB binned by nominal crystallographic resolution.

This compensatory change in Φ, Ψ is due to a “crankshaft” motion [39] of the amide bond that maintains the relative positions of the α-carbons of the peptide backbone despite significant deviations in Φ, Ψ torsions.