Fig. 2

Complete datasets of helix termini. Loop backbone structures for the complete datasets of 24,880 N-terminal peptides (top row) and 15,368 C-terminal peptides (bottom row) are plotted at the α carbons in the helix-terminal coordinate systems for each terminus, and viewed from 3 perspectives in each case. At the N-terminus, perspectives are: (a) from (+z), (b) from (+x), and (c) from (−z). At the C-terminus, perspectives are: (d) from (+z), (e) from (+x), and (f) from (−z). At the N-terminus, loop residues N'''-N''-N'-NCap are plotted, while at the C-terminus loop residues C”’-C”-C’-CCap are shown. Loop structures show a broad range of geometries, with areas of higher density towards (+x, −y) at the N-terminus (ST-motifs, capping boxes) and (+x, +y) at the C-terminus (Schellman loops). Not all loop structures are visible, as some structures are concealed by others