Peptide plane flipping is a type of conformational change that can occur in proteins by which the dihedral angles of adjacent amino acids undergo large-scale rotations with little displacement of the side chains.
The key requirement is that the sum of the ψi angle of residue i and the φi+1 angle of residue i+1 remain roughly constant; in effect, the flip is a crankshaft move about the axis defined by the Cα-C¹ and N-Cα bond vectors of the peptide group, which are roughly parallel.
[1] For example, peptide flips have been described as significant in the catalytic cycle of flavodoxin[2] and in the formation of amyloid structures, where their ability to provide a low-energy pathway between beta sheet and the so-called alpha sheet conformation is suggested to facilitate the early stages of amyloidogenesis.
[3][4][5] Peptide plane flipping may also be significant in the early stages of protein folding.
[1] In protein structures determined by X-ray crystallography, poor peptide-plane geometry has been described as a common problem; many structures need correction by peptide-plane flips or peptide bond flips.