Characterization at atomic resolution of peptide helical structures

A survey of literature for the various types of helices experimentally observed in highresolution single crystal x-ray diffraction analyses of peptides has allowed to determine accurate conformational and helical parameters for the various secondary structures such as the α-helix, the 310-helix, the fully extended conformation (25-helix) and the β-bend ribbon spiral. For each of these structures the characteristic ϕ, ψ conformational parameters, n, the number of residues per turn, h, the height per residues and p, the pitch of the helix are described.