MECHANISM OF ALLERGENIC CROSS-REACTIONS .5. EVIDENCE FOR PARTICIPATION OF AROMATIC RESIDUES IN THE LIGAND-BINDING SITE OF 2 MULTI-SPECIFIC IGE MONOCLONAL-ANTIBODIES

The binding sites of two IgE monoclonal antibodies (mAbs), LA2 and LB4 , were examined by absorption, fluorescence spectroscopy and computer- aided molecular modeling (CAMM). Absorption spectra revealed the forma tion of 1:1 molecular complexes for both LA2 and LB4 with a variety of structurally different ligands. For mAb LA2, the binding constants fo r ligands consisting of different amino acid derivatives coupled to DN P could be divided into two groups, suggesting that certain amino acid side chains (e.g. hydrophobic) of the derivatives were a contributing feature in ligand recognition. The presence of a charge-transfer band (320-340 nm) was also observed for complexation with several differen t ligands, indicative of aromatic ligand interactions with mAb binding site tryptophans. CAMM studies of the Fv region for both mAb support of the empirical observations and inspection of the Fv models reveal n umerous binding site aromatic residues that are likely candidates for ligand recognition and complexation. The multispecificity of these mAb s for different ligands may be due to a multitude of interactions with aromatic residues in the binding sites.