Table 1. Calculated Absorption Shifts in Units of Nanometer for the Site-Directed Mutants Y21F, Y21I, Y21W, Q63E (neutral, where the proton forms a permanent hydrogen bond to C4=O), and Q63L and the Enol Tautomerization of Gln63 Using the Structural Data from Different Crystal Structures That Contain Different Coordinates Sets (first column) Which Can Be Assigned to the Q63A and Q63J Structural Models (second column); Experimental Absorption Shifts Are Given in the Last Row (calculated absorption shifts in kilocalorie per mole are given in Table S7 in the Supporting Information).
| type | Y21F | Y21I | Y21W | Q63E | Q63Ea | Q63L | Q63Qenol a | Q63Qrotenol a | |
|---|---|---|---|---|---|---|---|---|---|
| 1YRX A | Q63A | +5.7 | +5.6 | +6.3 | +20.8 | +21.3 | +13.6 | n/a | n/a |
| 1YRX B | Q63A | +5.1 | +5.0 | +5.4 | +19.0 | +21.4 | +13.1 | n/a | n/a |
| 1YRX C | Q63A | +4.8 | +4.7 | +5.2 | +25.0 | +24.2 | +15.4 | n/a | n/a |
| 2HFN D | Q63A | +5.3 | +5.0 | +6.0 | +20.2 | +20.1 | +14.3 | n/a | n/a |
| 1X0P A | Q63J | –5.2 | –5.4 | –4.7 | +7.4 | +4.8 | –4.1 | +9.0 | +13.2 |
| 1X0P B | Q63J | –4.9 | –5.1 | –4.4 | +9.6 | +4.2 | –2.2 | +9.8 | +14.3 |
| 1X0P C | Q63J | –4.9 | –5.2 | –4.4 | +5.0 | +4.0 | –7.2 | +6.3 | +10.6 |
| 1X0P D | Q63J | –4.9 | –5.2 | –4.5 | +9.3 | +4.9 | –2.8 | +10.6 | +14.2 |
| 1X0P E | Q63J | –4.6 | –4.8 | –4.3 | +5.8 | +4.6 | –5.0 | +7.3 | +10.8 |
| 1X0P F | Q63J | –4.7 | –5.1 | –4.3 | +8.9 | +4.0 | –3.0 | +10.2 | +13.6 |
| 1X0P G | Q63J | –4.8 | –5.1 | –4.4 | +7.8 | +4.2 | –3.4 | +8.4 | +13.0 |
| 1X0P H | Q63J | –5.2 | –5.5 | –4.7 | +9.1 | +4.4 | –2.0 | +10.7 | +14.0 |
| 1X0P I | Q63J | –4.7 | –5.0 | –4.3 | +7.6 | +3.5 | –3.3 | +10.3 | +12.7 |
| 1X0P J | Q63J | –5.1 | –5.4 | –4.8 | +8.6 | +5.2 | –2.9 | +10.3 | +13.1 |
| 2HFN A | Q63J | –4.7 | –5.0 | –4.0 | +5.7 | +4.5 | –6.2 | +9.2 | +9.9 |
| 2HFN B | Q63J | –4.7 | –4.9 | –4.0 | +5.7 | +3.7 | –5.1 | +9.3 | +9.8 |
| 2HFN C | Q63J | –4.5 | –4.7 | –4.2 | +5.8 | +4.8 | –5.8 | +8.9 | +9.7 |
| 2HFN E | Q63J | –4.7 | –4.9 | –3.9 | +5.3 | +5.6 | –5.6 | +8.3 | +9.6 |
| 2HFN F | Q63J | –4.6 | –4.9 | –4.0 | +5.0 | +4.4 | –5.9 | +8.6 | +9.3 |
| 2HFN G | Q63J | –4.9 | –5.2 | –4.2 | +6.0 | +4.9 | –5.6 | +10.9 | +10.9 |
| 2HFN H | Q63J | –4.6 | –5.0 | –4.0 | +4.8 | +4.5 | –5.4 | +9.2 | +9.5 |
| 2HFN I | Q63J | –4.6 | –4.9 | –4.3 | +6.8 | +4.7 | –4.9 | +11.0 | +11.1 |
| 2HFN J | Q63J | –4.3 | –4.5 | –3.6 | +5.5 | +4.1 | –6.3 | +7.7 | +9.3 |
| 2IYG A | Q63J | –6.0 | –6.2 | –5.1 | +5.2 | +2.8 | –6.5 | +9.3 | +10.3 |
| 2IYG B | Q63J | –5.3 | –5.4 | –4.6 | +6.3 | +2.4 | –7.9 | +9.3 | +10.2 |
| measured value | –2/–4b | –4c | –4d | +3e | +3e | –6/–10f | +10 to +15g | +10 to +15g | |
a
The side-chain orientation of Gln63 has been manipulated in order to simulate the hydrogen bond distance between the side-chain amide and the C4=O of the isoalloxazine as related for the light-adapted state according to spectroscopic data (see text).
b
See refs (79 and 80) (the exact value was not given in ref (80), but from an overlay of the wild type and mutant absorption spectra, we could estimate the difference of the absorption maximum with an uncertainty of roughly 2 nm).
c
See ref (78).
d
See ref (33).
e
See ref (55).