The relationship between the 23-state structural alphabet and three-state secondary elements. (a) The three-dimensional (3D) segment conformations of the five main classes of the 23-state structural alphabet, including helix letter (A, Y, B, C, and D), helix-like letters (G, I, and L), strand letters (E, F, and H), strand-like letters (K and N), and others (Additional data file 2). The shapes of the segments in the same category are similar to each other. (b) The distributions of the 23-state structural alphabet on 82,482 α-helix segments, 52,371 β-strand segments, and the 66,503 coil segments defined by the DSSP program.
Tung et al. Genome Biology 2007 8:R31 doi:10.1186/gb-2007-8-3-r31