Doubly sensitivity-enhanced 3D TOCSY-HSQC

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Abstract
Recently, strategies for double sensitivity enhancement in heteronuclear three-dimensional NMR experiments were introduced (Krishnamurthy, V.V. (1995) J. Magn. Reson., B106, 170–177; Sattler et al. (1995) J. Biomol. NMR, 6, 11–22; Sattler et al. (1995) J. Magn. Reson., B108, 235–242). Since a sensitivity enhancement of a factor 21/2 can be achieved for each indirect dimension, nD spectra can theoretically be enhanced up to a factor of 2((n-1)/2). We propose and analyze a doubly enhanced three-dimensional TOCSY-HSQC sequence. The application of the doubly enhanced three-dimensional {15N, 1H} TOCSY-HSQC sequence is shown for uniformly 13C-/15N- and 15N-labeled samples of the relatively large Azotobacter vinelandii flavodoxin II (179 amino acids). The main factors that contribute to the final signal-to-noise enhancement have been systematically investigated. The sensitivity enhancement obtained for the doubly enhanced TOCSY-HSQC pulse sequence as compared to the standard (unenhanced) version is close to the theoretically expected factor of two.