Isotope-detected 1H NMR studies of proteins: a general strategy for editing interproton nuclear Overhauser effects by heteronuclear decoupling, with application to phage lambda repressor.

A strategy for editing interproton nuclear Overhauser effects (NOEs) in proteins is proposed and illustrated. Selective incorporation of 13C- (or 15N)-labeled amino acids into a protein permits NOEs involving the labeled residues to be identified by heteronuclear difference decoupling. Such heteronuclear editing simplifies the NOE difference spectrum and avoids ambiguities due to spin diffusion. Isotope-detected 1H NMR thus opens to study proteins too large for conventional one- and two-dimensional NMR methods (20-75 kDa). We have applied this strategy to the N-terminal domain of phage lambda repressor, a protein of dimer molecular mass 23 kDa. A tertiary NOE from an internal aromatic ring (Phe-51) to a beta-13C-labeled alanine residue (Ala-62) is demonstrated.