Similar fragment pairs exist in different domain interactions. Fragment pairs of two helices are located at the interfaces of two different domain interactions in (a) and (b). Two fragments form inter-molecular β-sheet in (c) and (d). One of these two structures is a homo-dimer and the other one is a heterodimer. Finally, similar LL motifs are found in very different binding interfaces, as shown in (e) and (f). The backbones of interacting protein domains are in red and green, while the fragment pair motifs at their interfaces are in yellow and blue with cartoon representation.