Table 10. Comparison of Interaction Energies for K+ Ion-Binding Proteins, Using QM Calculations, the C36 Additive Force Field, and the Drude Polarizable Force Fielda.
| 1JF8 |
1LJL |
|||||
|---|---|---|---|---|---|---|
| QM | C36 | Drude | QM | C36 | Drude | |
| ΔELig1 | –21 | –18 | –22 | –22 | –19 | –21 |
| ΔELig2 | –6 | –3 | –4 | –2 | –1 | –5 |
| ΔELig3 | –82 | –83 | –75 | –78 | –78 | –76 |
| ΔELig4 | –22 | –16 | –24 | –24 | –19 | –22 |
| ΔELig5 | –98 | –102 | –103 | –99 | –103 | –102 |
| ΔELig6 | N/A | N/A | N/A | N/A | N/A | N/A |
| ΔEW1 | 3 | 3 | –3 | 3 | 3 | 2 |
| ΔEW2 | 2 | 2 | –4 | –1 | –1 | –3 |
| ΔEW3 | –2 | –1 | –2 | –5 | –3 | –5 |
| ΔEW4 | –1 | –1 | –2 | 2 | 2 | 1 |
| ΔEW5 | –13 | –12 | –11 | –12 | –11 | –12 |
| ΔEIon | N/A | N/A | N/A | N/A | N/A | N/A |
| ΔESum | –239 | –233 | –250 | –237 | –230 | –243 |
| ΔEOverall | –196 | –233 | –201 | –196 | –230 | –201 |
| ΔΔE | –43 | 0 | –49 | –41 | 0 | –42 |
a
Lig1 to Lig6 represent different peptide segments in the truncated proteins. W1 to W5 represent different water molecules. ΔESum is the sum of interaction energies for all individual ion–ligand, ion–water, and ion–ion pairs. ΔEOverall is the overall QM interaction energy by treating all the ligands, water molecules and other ions as a whole system. The non-additive energy ΔΔE = ΔESum – ΔEOverall. All values in kcal/mol are averaged for 20 frames extracted from 4 ns simulations.