Comparison of immunoglobulin heavy-chain variable (VH) and fibronectin type III (FN3) domains and monobody library designs. (A) β-Strand and loop topology. The two β-sheets of the corresponding domains are shown in an open book manner with the dashed lines indicating the boundary between the two β-sheets. SS denotes an intradomain disulfide bond. (B) Cartoon representation of VH (PDB ID: 1VFB) and FN3 (3CSB). The complementarity-determining regions (CDRs) are according to the Kabat definition (Wu et al. 1993). (A,B, Drawn based on Fig. 1 in Koide et al. 1998.) (C,D) Two distinct types of monobody library designs. An antibody-like library design is depicted in C, and a non-antibody-like, “side” library is shown in D. (C,D, Modified from Fig. 1 in Koide et al. 2012a, with permission.)