Table 1.
pKa values for ubiquitin amines derived from pH titration series recorded by 1H-15N H2CN or 1H-13C HSQC experiments, using the indicated nuclei as reporters
| Amine | 15Nζ | 1Hε (H2CN) | 13Cε | 1Hε (HSQC) |
|---|---|---|---|---|
| M1 | -- | -- | 9.19 ± 0.05 | 9.21 ± 0.01 |
| K6 | 10.47 ± 0.02 | 10.57 ± 0.03 | 10.5 ± 0.1 | 10.55 ± 0.04 |
| K48 | 10.53 ± 0.02 | 10.72 ± 0.06 | -- | -- |
| K33 | 10.88 ± 0.03 | 10.99 ± 0.03 | 10.8 ± 0.1 | 10.73 ± 0.06 |
| K63 | 11.03 ± 0.02 | 11.06 ± 0.03 | 11.0 ± 0.1 | 11.5 ± 0.2a |
| K27 | -- | -- | 11.2 ± 0.1 | 11.5 ± 0.1b |
| K11 | 11.47 ± 0.03 | 11.46 ± 0.07 | -- | -- |
| K29 | 11.68 ± 0.03 | 11.85 ± 0.03 | -- | -- |
a
Peak overlap in the proton dimension of the HSQC experiments for K63 decreased the accuracy in calculating this pKa.
b
The proton resonances for K27 are degenerate at lower pH values but begin to split into unique resonances as the pH is increased. This is combined with exchange broadening at elevated pH which limited an accurate proton chemical shift determination and decreased the accuracy in this calculated pKa.