SECONDARY FORCE-MEDIATED PERTURBATIONS OF ANTIFLUORESCEIN MONOCLONAL-ANTIBODIES 4-4-20 AND 9-40 AS DETERMINED BY CIRCULAR-DICHROISM

Secondary forces have been defined as those interactions between antib ody and antigen that occur external to the antibody active site. Previ ous investigations indicated that non-active-site secondary interactio ns can modulate immune complex stability and may influence antibody va riable domain conformation and/or dynamics. To assess secondary force- induced perturbations of monoclonal antibodies 4-4-20 and 9-40 a serie s of monofluoresceinated peptides was reacted and the various interact ions analyzed by circular dichroism (CD). The mAbs 4-4-20 and 9-40 var y by nearly 1000-fold in their respective affinities for the fluoresce in ligand, yet both immunoglobulins are highly related at the primary structural (idiotype) level. Near-UV CD spectra were evaluated as well as the induced optical activity (visible CD) of the antibody-bound fl uorescein moiety when covalently attached to various peptide carriers. Comparative spectral studies revealed significant differences in the near-UV CD spectra of mAbs 9-40 and 4-4-20 relative to the various pep tide antigens and to one another. CD spectra were interpreted as refle cting differential secondary force-induced perturbations of the antibo dy variable domains as well as intrinsic differences between the two m Abs.