Role of the domain-domain interaction in the construction of the antigen combining site. A comparative study by 1H-15N shift correlation NMR spectroscopy of the Fv and Fab fragments of anti-dansyl mouse monoclonal antibody.

A comparative NMR structural study of anti-dansyl Fv and Fab fragments is reported. Both of these antigen binding fragments have been prepared using antibodies that originate from the identical anti-dansyl switch variant cell lines. It has been confirmed that the Fv and Fab fragments possess the identical binding property. The antigen binding fragment analogs labeled with 15N of the main chain amide group of the aromatic residues (His, Phe, Trp, and Tyr) were used. The chemical shift and hydrogen-deuterium exchange rate of the amide protons are compared for the Fv and Fab fragments. On the basis of the NMR data obtained, we have concluded that (1) the structural change induced in the VH domain upon antigen binding significantly affects the dynamical structure of the VL domain and (2) the existence of the constant regions affects the fluctuation of the VL domain, increasing the thermal stability of the variable region.