Epitope Mapping Antibody-Antigen Complexes by Nuclear Magnetic Resonance Spectroscopy

NMR
spectroscopy has been used to study antibody complexes with antigenic peptides. A crucial parameter in NMR studies of large biological complexes is the rate of exchange of a ligand between its free and bound states. In cases where the peptide off-rate is fast (faster than 10 s
−1
) relative to the decay of magnetic excitation (longitudinal relaxation time) and to the inverse of the mixing period (the time during which magnetization transfer takes place) used in NOESY* experiments, transferred NOE (TRNOE) techniques, including 2D TRNOE difference spectroscopy (
1
) and the T
1ρ
-filtered TRNOE method (
2
), are very suitable to study antibody-antigen interactions and intramolecular interactions within the bound peptide (
3
). Alternatively, in the case of tight binding and slow exchange, isotope filtering methods can be applied (
4
). Tsang et al. (
5
) used this technique to elucidate amide proton interactions in an antibody-bound peptide complex and to characterize the mobility of these protons on binding.