Schematic representations of different types of π-turns indicating the numbering of the positions. (i+1) to (i+4) positions are defined as the middle residues. a-c) Hydrogen-bonded turns using main-chain CO and NH groups. The presence of hydrogen bond is shown by solid line connecting (i) and (i+5) residue. For each position the corresponding DSSP notation is shown below. For the π-NHB turns the terminal interaction is shown by a dotted line. a) Isolated π-turn (π-HB), with middle residues in turn (T, by DSSP notation); b) SCH+β, where (i) to (i+2) positions are in helical conformation (H, by DSSP notation) and there is an additional hydrogen bond linking (i+1) and (i+4) positions; c) SCH-β, which is different from SCH+β in that the additional hydrogen bond is missing; d) Non-hydrogen-bonded π-turn (π-NHB) (see text).
Dasgupta and Chakrabarti BMC Structural Biology 2008 8:39 doi:10.1186/1472-6807-8-39