Orientation of antigen binding sites in dimeric and trimeric single chain Fv antibody fragments

Electron microscopy of dimeric and trimeric single chain antibody Fv fragments (scFvs) complexed with anti-idiotype Fab fragments was used to reveal the orientation of antigen binding sites. This is the first structural analysis that discloses the multivalent binding orientation of scFv trimers (triabodies), Three different scFv molecules were used for the imaging analysis; NC10 scFv-5 and scFv-0, with five- and zero-residue linkers respectively between the V(H) and V(L) domains, were complexed with 3-2G12 anti-idiotype Fab fragments and 11-1G10 scFv-0 was completed with NC41 anti-idiotype Fab fragments. The scFv-5 molecules formed bivalent dimers (diabodies) and the zero-linker scFv-0 molecules formed trivalent trimers (triabodies), The images of the NC10 diabody-Fab complex appear as boomerangs, not as a linear molecule, with a variable angle between the two Fab arms and the triabody-Fab completes appear as tripods. (C) 1998 Federation of European Biochemical Societies.