Antigen recognition by an antibody light chain.

A monoclonal antibody to vasoactive intestinal polypeptide (VIP) was reduced and alkylated and its light and heavy chains were purified by denaturing gel filtration. Following renaturation, the light chain displayed sequence-specific binding of VIP. The specific VIP binding activity of several fractions spanning the light chain peak recovered from the gel filtration column was constant, the light chain was electrophoretically homogeneous, the VIP binding activity was precipitated by anti-light chain antibody but not anti-heavy chain antibody and the activity remained associated with a light chain fraction recovered by resolutive chromatography on a hydroxylapatite column. N-terminal amino acid sequencing of the light and heavy chain fractions confirmed the purity of these proteins and suggested that the VL and VH regions belonged to kappa-family II and gamma-family III, respectively. The VIP-binding affinity of the light chain was only 5-fold lower than that of the parent antibody and the light chain did not bind unrelated peptides. These observations suggest that light chains display structural characteristics necessary for high affinity antigen binding.