Mapping polypeptide self-recognition through (1)H off-resonance relaxation.

1H NMR relaxation rates provide a readily available and sensitive probe ideally suited to investigate the weak (KD approximately micromolar to millimolar range) interactions that frequently mediate polypeptide oligomerization in the early steps of amyloid fibrillogenesis. However, the measurement of transverse and longitudinal 1H relaxation rates is experimentally challenging due to J-transfer and selectivity problems in CPMG and inversion-recovery experiments, respectively. We show here that these problems are effectively circumvented by measuring nonselective off-resonance relaxation rates using an effective field tilted by 35.5 degrees . When applied to the Halpha spins of the Abeta (12-28) peptide, the proposed experiment provides a residue-resolution self-recognition map which is fully consistent with previous independent mutational studies. The method is anticipated to be widely applicable not only to the fast growing family of amyloidogenic peptides but also to the screening and mapping of protein-ligand interactions in general.