UNAMBIGUOUS NOE ASSIGNMENTS IN PROTEINS BY A COMBINATION OF THROUGH-BOND AND THROUGH-SPACE CORRELATIONS

Heteronuclear editing has found widespread use in the detection of pro ton-proton dipolar interactions in isotopically labelled proteins. How ever, in cases where both the resonances of protons and directly bound C-13 or N-15 spins of two or more sites are degenerate, unambiguous a ssignments are difficult to obtain by conventional methods. Here, we p resent simple extensions of well-known triple-resonance pulse sequence s which improve the dispersion of NOESY spectra. In order to record th e chemical shifts of backbone nuclei which allow a resolution of overl apping cross peaks, the magnetization is relayed via the scalar coupli ng network either before or after the NOE mixing period. The novel pul se sequences are applied to flavodoxin from the sulfate-reducing organ ism Desulfovibrio vulgaris. A number of previously unassigned NOE inte ractions involving alpha-, beta- and amide protons can be unequivocall y identified, suggesting that the accuracy of protein structure determ ination can be improved.