Structural studies on antibodies

Data from ¹H nuclear magnetic resonance studies on the Fv fragment of protein 315, a Dnp-binding BALB/c mouse lgA(λ₂) myeloma protein, have been used to refine a predicted structure of the combining site of the protein. The Dnp-binding subsite in the modified structure is composed of the side chains of three aromatic amino acids Trp 93_L, Tyr 3⁴_L and 3⁴_H. A fourth aromatic amino acid residue is close to the side chain-NH-CH 2 -group, this is Tyr 33 H - The antibody-hapten binding is a simple encounter process, which causes no extensive conformation change in the Fv fragment. A method for paramagnetic structural studies has been devised using Dnp derivatives with cllgophosphate side chains, which create a specific manganese binding site on the Fv fragment-hapten complex. The distances from the bound metal ion to the imidazole side chains of two of the three hlstldine residues of protein 315 have been determined. ¹H nuclear magnetic resonance has been used to study the histidine residues of the Fv fragment of protein 315. It has been shown that one of the three histidine residues (102_H) is close to the combining site, but that this residue does not participate directly in binding haptens. ³¹ P nuclear magnetic resonance studies have shown the presence of a positively charged amino acid side chain near the entrance of the combining site of the Fv fragment. This residue has been identified as Arg 95_L. The mode of binding of trini trophenyl derivatives to the Fv fragment has been studied by ¹H nuclear magnetic resonance. It is concluded that these haptens, when bound to the Kv fragment, make contacts with the same amino acid side chains as Dnp derivatives.