The Versatility of Framework Regions of Chicken V(H) and V(L) to Mutations

To identify the interchangeability of V(H) and V(L) framework region (FR) residues, we artificially introduced random mutations at all residue positions in a chicken monoclonal antibody, which has only one functional V(H) and V(λ) gene. When we classified the amino acids into 5 groups by their physicochemical properties, all FR residues could be replaced by another group except L23 (C), H36 (W), H86 (D), H104 (G), and H106 (G). Eighty-two (50.9%), 48 (29.8%), 17 (10.6%), and 9 FR residues (5.6%) could be replaced by 4, 3, 2, and 1 group(s), individually, without significant loss of reactivity. We also confirmed a similar level of versatility with 2 different chicken antibodies. This high level of versatility on FR residues has not been predicted because it has not been observed in the 150 chicken antibodies that we previously generated or in the 1,269 naïve chicken V(H) sequences publically available. In conclusion, chicken antibody FR residues are highly interchangeable and this property can be applied for improving the physicochemical property of antibody including thermal stability, solubility and viscosity.