Suppression of diagonal peaks in three-dimensional protein NMR TROSY-type HCCH correlation experiments

A novel method for suppression of (13)C-(13)C diagonal peaks without sensitivity loss in three-dimensional HCCH TROSY-type NMR correlation experiments involving aromatic side chains in proteins (Pervushin et al., J. Am. Chem. Soc. 120, 6394-6400 (1998)) is presented. The key element is a spin-state-selective filter in the (13)C-(13)C mixing sequence with the dual effect of selecting the TROSY resonance in the preceding evolution period and interchanging TROSY and anti-TROSY resonances. The cross peaks are invariant to this filter but diagonal peak coherence gets concentrated on the anti-TROSY transition so that it can be eliminated by a (13)C --> (1)H TROSY transfer element. The new method is demonstrated using a (13)C,(15)N-labeled protein sample, RAP 18-112 (N-terminal domain of alpha(2)-macroglobulin receptor associated protein), at 750 MHz.