Drug-antiserum molecular interactions: a Raman spectroscopic study

Abstract

The binding of the phenytoin (5,5-diphenyl-2,4-imidazolidinedione) antiserum with its specific antigen and other chemicals with very low cross-reactivity coefficients was studied by means of Raman spectroscopy. The experimental results indicate that the predominant secondary structure of this antiserum is the β-sheet conformation and that the interaction with the ligands is able to modify the overall structure of the protein. The antiserum – antigen binding causes a slight decrease in the random conformation in all systems, whereas the changes in the β-sheet and α-helix content depend on the nature of the ligands. Ligands with a high cross-reactivity coefficient increase the α-helix percentage, whereas the opposite effect is observed with low cross-reactivity ligands. The stereochemical properties of the substituents in the 5-position of the heterocyclic ring, relative to the rest of the molecule, are an important factor in determining the cross-reactivity and the kind of interaction with the antiserum. If in this position only one phenyl group is present, the antiserum – ligand affinity is low and the α-helix percentage decreases, but when in this position two phenyl groups are present, the affinity is high and the α-helix percentage increases. As regards the tertiary structure of the antiserum protein, alkyl side-chains and Trp residues contribute to the stability of the antiserum-specific antigen complex by means of hydrophobic interactions. The spectral features of alkyl side-chains and Trp do not change in the presence of ligands with low affinity. Copyright © 1999 John Wiley & Sons, Ltd.