Table 1

Transverse 1HN and 15N relaxation rates predicted for a 23-kDa protein at 750 MHz in [15N, 1H]-TROSY-HNCA and in conventional HNCA*

TROSY-HNCA HNCA Gain
R2T(15N)[s−1]R2T(1HN) [s−1]R2C(15N) [s−1]R2C(1HN) [s−1]AT/AC
Isolated 15N–1HN group3.03.220.920.38.0
β-sheet 13C/15N-labeled10.641.128.558.21.8
α-helix 13C/15N-labeled§8.731.526.648.62.0
β-sheet 2H/13C/15N-labeled3.76.321.623.54.7
α-helix 2H/13C/15N-labeled5.013.222.930.32.9
  • * 15N and 1HN relaxation rates were calculated using Eqs. 6 and 7, respectively, as described in the text. The values listed for conventional HNCA are the average relaxation rates of both components of the 15N and the 1HN doublets, given by RsN and RrN, and by RsH and RrH, respectively. The following parameters were used: rHN = 1.04 Å (39), ΔσN = 155 ppm, ΔσH = 15 ppm, ΘN = 15°, ΘH = 10° (40), and τc = 15 ns. 

  • AT and AC are the relative signal intensities obtained with [15N, 1HN]-TROSY-HNCA and conventional HNCA. The ratio AT/AC was calculated with Eq. 8, using T = 52 ms. 

  • Remote protons considered are 1HN (i − 1), 1HN (i + 1), 1HN (j), 1Hα (i), 1Hα (i − 1), 1Hα (j), 1Hβ (i), and 1Hβ (i − 1) at distances of 4.3, 4.3, 3.3, 2.8, 2.2, 3.2, 2.5, and 3.2 Å, respectively, which are typical for an antiparallel β-sheet [i is the observed residue, (i − 1) and (i + 1) the sequential neighbors, and j indicates a long-range contact across the β-sheet (2)]. 

  • § Remote protons are 1HN (i − 1), 1HN (i + 1), 1HN (i − 2), 1HN (i + 2), 1Hα (i), 1Hα(i − 1), 1Hα(i − 2), 1Hα(i − 3), 1Hα(i − 4), and 1Hβ(i) at distances of 2.8, 2.8, 4.2, 4.2, 2.6, 3.5, 4.4, 3.4, 4.2, and 2.5 Å, respectively, which are typical for an α-helix (2). 

  • Remote protons are 1HN (i − 1), 1HN (i + 1), and 1HN (j) at 4.3, 4.3, and 3.3 Å (2). 

  • Remote protons are 1HN (i − 1), 1HN (i + 1), 1HN (i − 2), and 1HN (i + 2) at 2.8, 2.8, 4.2, and 4.2 Å (2).