A few illustrative examples of (a) Schellman motif and (b,c) β-hairpin motifs formed by using some of the π-HB and π-NHB turns of different conformations. The PDB code of each structure is given in the bottom with chain identity; the starting and end residue numbers are given in parentheses, indicating the location of the π-turn. For each residue in π-turn along with the terminal residues, the secondary structural element is indicated in accordance to DSSP. a) Schellman motif formed at the end of an α-helix. Labels of positions are given in parentheses. Hydrogen bonds are shown as dashed lines (the (i) ← (i+4) hydrogen bond is intrahelical). The residue at (i+4) position is Gly. b) π-HB turns in between β-strands. The left structure is in conformation AAAa and the right pAAa. c) Two examples of π-NHB turns (with EAAa conformation) forming β-hairpin motif.
Dasgupta and Chakrabarti BMC Structural Biology 2008 8:39 doi:10.1186/1472-6807-8-39