Table 2A.
Effect of His108Ala (H108A), Asp144Ala (D144A) theoretical mutations and His108 κ2-torsion angle flip on the pKas of key residues/groups for catalysis, using crystallographic structures 1cdeH108(Nɛ2H) and 1cdeH108(Nɛ2H)/flipa
| 1cdeH108(Nɛ2H) | 1cdeH108(Nɛ2H)/flip | ||||
| κ2(H108) = 0° | κ2(H108) = 180° | ||||
| WTc | H108A | D144A | D144A | WT | |
| Ionizable residue/groupb | pKa (apparent) | ||||
| HIS54 | 7.2 | 7.2 | 7.2 | 7.1 | 7.2 |
| HIS73 | 6.6 | 6.6 | 6.6 | 6.6 | 6.6 |
| ARG90d | 15.9 | 15.9 | 15.8 | 15.8 | 15.9 |
| HIS99 | 6.0 | 6.0 | 6.0 | 5.9 | 6.0 |
| HIS108 | 6.9 | 2.6 | −1.2 | 3.9 | |
| HIS119 | 5.7 | 5.8 | 5.7 | 5.6 | 5.7 |
| HIS121 | 7.0 | 7.0 | 7.0 | 7.0 | 6.9 |
| HIS132 | 0.4 | 1.0 | 0.4 | 0.7 | 0.5 |
| HIS137 | 2.0 | 3.5 | −0.6 | 0.2 | 2.4 |
| ASP144 | −2.3 | −0.5 | −2.4 | ||
| GLU173 | 1.7 | 2.4 | 2.1 | 2.5 | 1.9 |
| HIS174 | 6.8 | 6.8 | 6.8 | 6.8 | 6.8 |
| TYR177d | 15.7 | 15.7 | 15.2 | 15.3 | 15.8 |
| HIS192 | 6.3 | 6.3 | 6.3 | 6.3 | 6.3 |
| GAR(NH2) | 5.8 | 8.1 | 4.7 | 6.8 | 8.6 |
| GAR PO42− | 2.7 | 2.6 | 2.6 | 2.6 | 2.6 |
| GAR PO4− | <−5 | <−5 | <−5 | <−5 | <−5 |
| 5dTHF HN3-C4=O | 10.9 | 10.8 | 9.8 | 9.8 | 10.9 |
| 5dTHF CγOO− | 2.7 | 2.7 | 2.6 | 2.6 | 2.7 |
| 5dTHF CαOO− | 2.6 | 2.7 | 2.4 | 2.5 | 2.6 |
a The side chain of His108 possesses initial hydrogen at Nɛ2.
b Besides all 10 histidines, Asp144, GAR, and 5dTHF, residues with relative pKa shifts >1 pKa unit within the 10 calculations of Tables 2A and 2B, are shown. Significant pKa perturbations because of mutations or His108 flip state are in bold face. pKa perturbations attributed to substrate binding (Tables 2A, 2B) are in italics.
c WT stands for wild type and refers to the parent structure.
d The pKas of Arg90 and Tyr177 are very high to be of significant biological relevance, but they are listed here to show their interaction with substrate/cofactor, possibly important for binding.