Unambiguous NOE assignments in proteins by a combination of through-bond and through-space correlations

Abstract

Heteronuclear editing has found widespread use in the detection ofproton–proton dipolar interactions in isotopically labelled proteins.However, in cases where both the resonances of protons and directly bound13C or 15N spins of two or more sites aredegenerate, unambiguous assignments are difficult to obtain by conventionalmethods. Here, we present simple extensions of well-known triple-resonancepulse sequences which improve the dispersion of NOESY spectra. In order torecord the chemical shifts of backbone nuclei which allow a resolution ofoverlapping cross peaks, the magnetization is relayed via the scalarcoupling network either before or after the NOE mixing period. The novelpulse sequences are applied to flavodoxin from the sulfate-reducing organismDesulfovibrio vulgaris. A number of previously unassigned NOE interactionsinvolving α-, β- and amide protons can be unequivocallyidentified, suggesting that the accuracy of protein structure determinationcan be improved.