Distributions of C
, C, N, O atoms in Frenet frames. (Color online) a) Distribution of Cβ atoms in the Cα centered Frenet frames in PDB structures that have been measured with better than 1.0 Å resolution. The three major structures α-helices, β-strands and left-handed α-helices have been marked, following their identification in PDB. b) Same as a) but for backbone C atoms. Note that C atoms that precede a cis-proline are clearly identifiable. c) Same as a) and b) but for backbone N atoms. d) Same as a), b) and c) but for backbone O atoms. As in b) the atoms preceding a cis-proline are clearly identifiable.