Third type of secondary structure: noncooperative mobile conformation. Protein Data Bank analysis

Analysis of 68 proteins from Protein Data Bank disclosed a new widely spread type of the secondary structure that is designated as mobile (M-) conformation. Helical parameters of M-conformation are close to the poly-L-proline II type helix. Its occurrence in globular proteins approximates that of the beta-sheet. The angles corresponding to the position of the M-conformation maximum in distribution of amino acid residues on a conformational map are phi: -65 degrees, psi: 140 degrees. Unique features and high occurrence in proteins make it possible to distinguish the M-conformation as an independent third type of the secondary structure in globular proteins, that should be included in the present classification.