Table 1. FRET distance measurements within the cardiac troponin complex.
| Acceptor | Donor | Ca2+-saturated state | Ca2+-free state | ||
| TnT-240 | TnI- | FRET(HW) Å | 11.1 ns Å | FRET(HW) Å | 9.5 ns Å |
| DABMI | 131 AEDANS | 48.1(10.2) 38.13 | 50.89 | 47 (11.7) | 48.49 |
| DABMI | 145 AEDANS | 55.6(14.3) | 54.17 | 58.1(14.4) | 59.29 |
| DABMI | 151 AEDANS | 66.9(12.8) 60.52 | 67.34 | 63.9(18.0) | 60.50 |
| DABMI | 160 AEDANS | 73.3(18.1) 72.57 | 73.37 | 70.7(21.8) | 71.09 |
| DABMI | 167 AEDANS | 78.4(19.9) 76.93 | 79.49 | 76.7(35.5) | 72.95 |
| TnT-276 | TnI- | ||||
| DDPM | 131 MIANS | 20.4(1.2) 18.21 | 21.87 | 19.1 (3.6) | 14.36 |
| DABMI | 145 AEDANS | 34.3(11.2) | 37.36 | 28.2(10.7) | 32.79 |
| DABMI | 151 AEDANS | 53.6(14.3) 45.24 | 56.09 | 44.7(21.9) | 41.60 |
| DABMI | 160 AEDANS | 51.8(10.7) 57.12 | 55.21 | 54.2(20.7) | 52.56 |
| DABMI | 167 AEDANS | 61.3(20.5) 66.12 | 65.83 | 62.3(29.2) | 60.43 |
| DABMI | 17 AEDANS | 54.6(16.0) | 53.26 | 50.0(15.4) | 48.82 |
| DABMI | 27 AEDANS | 45.1 (9.1) | 44.92 | 47.4(11.0) | 47.39 |
| DABMI | 40 AEDANS | 38.0 (13.6) | 40.00 | 39.4(19.3) | 45.09 |
| TnT-288 | TnI- | ||||
| DDPM | 131 MIANS | 25.9(4.1) | 21.87 | 26.1(8.8) | 22.90 |
| DABMI | 145 AEDANS | 39.5(17.8) | 37.36 | 39.6(18.3) | 40.39 |
| DABMI | 151 AEDANS | 51.4(16.9) | 56.09 | 50.1(22.2) | 47.70 |
| DABMI | 160 AEDANS | 55(21.3) | 55.21 | 57.8(22.9) | 58.65 |
| DABMI | 167 AEDANS | 65.4(29.2) | 65.83 | 63.2(26.3) | 65.03 |
| DABMI | 5 AEDANS | 54.9 (5.6) | 58.59 | 56.8 (7.6) | 57.81 |
| DABMI | 17 AEDANS | 57.6(21.9) | 55.99 | 55.6(20.1) | 52.30 |
| DABMI | 40 AEDANS | 46.9(14.2) | 45.47 | 47.5(13.4) | 47.06 |
| TnC-12 | TnI- | ||||
| DDPM | 5 AEDANS | 42.6(4.7) | 42.07 | 45(7.5) | 42.85 |
| DDPM | 15 AEDANS | 39.9(3.3) | 41.92 | 43.4(11.6) | 44.38 |
| DDPM | 30 AEDANS | 41.3(16.6) | 41.24 | 42.1(16.5) | 42.60 |
| DDPM | 43 AEDANS | 38.8(16.3) | 36.33 | 36.3(6.9) | 35.65 |
| TnC-35 | TnI- | ||||
| DDPM | 5 AEDANS | 39.6(16.4) | 35.54 | 33.7(2.8) | 33.54 |
| DDPM | 15 AEDANS | 24.9(11) | 25.12 | 24.5(5.9) | 24.77 |
| DDPM | 30 AEDANS | 16(6.5) | 14.76 | 19.2(7.3) | 18.47 |
| DDPM | 43 AEDANS | 35.5(4.1) 33.65 | 31.10 | 36.2(4.4) | 34.07 |
| TnC-89 | TnI- | ||||
| DDPM | 5 AEDANS | 34.1(15.5) | 39.51 | 36.6(16) | 40.73 |
| DDPM | 15 AEDANS | 41.9(16.4) | 39.52 | 34.5(2.3) | 38.83 |
| DDPM | 30 AEDANS | 45.2(16.8) | 41.54 | 39.3(9.9) | 38.19 |
| DDPM | 43 AEDANS | 33.1(15.3) 21.43 | 29.04 | 37.8(16.2) | 37.0 |
| TnC-93 | TnI- | ||||
| DDPM | 5 AEDANS | 47.8(13.9) | 40.08 | 38.7(16.3) | 40.43 |
| DDPM | 15 AEDANS | 33.8(15.4) | 38.31 | 34.8(14.2) | 37.44 |
| DDPM | 30 AEDANS | 39.3(16.2) | 40.42 | 39.8(16.5) | 37.08 |
| DDPM | 43 AEDANS | 28.9(3.6) 22.84 | 24.99 | 39.1(14.4) | 37.20 |
| TnI-129 | TnI- | ||||
| Trp | 5 AEDANS | 24.62(8.165) | 33.85 | 41.2(20.4) | 42.11 |
| Trp | 15 AEDANS | 31.0(13.8) | 27.75 | 32.1(2.5) | 36.16 |
| Trp | 30 AEDANS | 27.9(2.5) | 27.33 | 30.4(12.1) | 33.76 |
| Trp | 43 AEDANS | 26.2(11.6) 33.22 | 27.10 | 35.2(14.6) | 40.39 |
| TnI-150 | TnI- | ||||
| Trp | 5 AEDANS | 31.2(1.2) | 31.92 | 34.9(2.0) | 34.76 |
| Trp | 15 AEDANS | 31.8(1.2) | 31.20 | 32.2(5.6) | 31.51 |
| Trp | 30 AEDANS | 29.7(10.5) | 30.42 | 20.5(2.5) | 25.77 |
| Trp | 43 AEDANS | 26.9(3.1) 24.50 | 27.42 | 29.1(10.9) | 27.25 |
| TnC-13C/51C [18] | 31 32.55 | 31.20 | 25.8 | 25.49 | |
| TnI-5 [22] IAANS | TnI-192 Trp | 51.5 | 52.06 | 46.8 | 46.94 |
The FRET distances measured between donor and acceptor probes in the Ca2+-saturated and the Ca2+-free states are tabulated. The half-widths are parenthesized. The FRET distances and restraints were applied as NOE restraints [49] between the Cα's of the participating amino acids. In columns 3,4 and 5,6 the experimentally measured FRET distance is tabulated along with the distance between the Cα's of the participating amino acids in the modeled structures, in the Ca2+-saturated states and Ca2+-free states respectively. In the FRET analysis, due to the ambiguity in the value of the dipole–dipole orientation factor between energy donor molecules and energy acceptor molecules and due to the dimensions of the probes attached by linkers to the side chains of the amino acid residues, the measured distance will have an uncertainty of ±10% [53]. Although the length of probe linkers is ∼10 Å, the linker is not unidirectional but folds randomly (during folding and rotation the probe and can acquire length of ∼7 Å). Based on these above factors there is good correlation between the measured FRET distance and the model. The italicized numbers in the third column pertain to the distance between the C-alphas in the crystal structure (1J1E). Compared to X-ray crystallography technique, FRET is a low resolution structural tool, and it does not have the lattice constraints that would be present in X-ray determined structure. However, FRET can acquire structural information in a more physiological environment, particularly with time-resolved approach (as we used here) it can provide dynamic information (represented by HW of the distance distribution) associated with each measured distance. Broad distributions of our FRET distances listed in Table 1 suggest that troponin exhibits a much dynamic structure in solution than in crystal. Therefore some discrepancies in the mean FRET distances with respect to the distances measured in X-ray structure would be expected. If we consider the structural dynamics (large HWs) observed in solution samples, these differences are in reasonable range.