Schematical representation of the structure of a conventional IgG and fragments that can be generated thereof. The constant heavy-chain domains CH1, CH2 and CH3 are shown in yellow, the constant light-chain domain (CL) in green and the variable heavy-chain (VH) or light-chain (VL) domains in red and orange, respectively. The antigen binding domains of a conventional antibody are Fabs and Fv fragments. Fab fragments can be generated by papain digestion. Fvs are the smallest fragments with an intact antigen-binding domain. They can be generated by enzymatic approaches or expression of the relevant gene fragments (the recombinant version). In the recombinant single-chain Fv fragment, the variable domains are joined by a peptide linker. Both possible configurations of the variable domains are shown, i.e. the carboxyl terminus of VH fused to the N-terminus of VL and vice versa.