Improved TROSY-HNCA experiment with suppression of conformational exchangeinduced relaxation

A general method for improving of the sensitivity of the TROSY-type triple resonance experiments in the presence of conformational exchange-induced (C SX) relaxation is proposed based on the use of CPMG-INEPT (Muller et al., J . Am. Chem. Soc., 1995, 117, 11043-11048) during the N-C polarization trans fer periods. Significantly improved sensitivity is demonstrated for the maj ority of cross-peaks in the new [N-15,H-1]-TROSY-XY-HNCA experiment, measur ed with partially folded RNase AS-Protein, with negligible loss of sensitiv ity for resonances unaffected by CSX relaxation. In addition, a comparison of cross-peak amplitudes in [N-15,N-1]-TROSY-XY-HNCA and conventional [N-15 ,H-1]-TROSY-HNCA spectra provides a quick and sensitive estimation of the C SX relaxation contribution.