TABLE 2.
Correspondence table for structurally conserved residues
Most functions are inferred from the structures of Ech-PME (as the D178A mutant) in complex with variously decorated hexasaccharides and from the changes in enzyme activity on mutation of selected residues (46). The PROPKA3-calculated pKa values of active-site residues are given in parentheses (96).
| Residue (structural element) | Ani-PME2 | Dca-PME | Ech-PME | Rice weevil PME | Function/comment |
|---|---|---|---|---|---|
| Thr (loop 3-2/3-3) | 83 | 109 | 146 | Substrate binding | |
| Gln (loop 4-2/4-3) | 145 | 115 | 153 | 177 | Substrate binding |
| Gln (loop 5-2/5-3) | 167 | 135 | 177 | 199 | Substrate binding/stabilization of anionic acyl intermediate |
| Asp (loop 5-2/5-3) | 168 (8.17) | 136 (9.06) | 178 (9.00) | 200 (8.51) | General acid/base |
| Asp (loop 6-2/6-3) | 189 (4.36) | 157 (4.89) | 199 (4.58) | 226 (4.39) | Positioned for nucleophilic attack on methyl ester moiety |
| Arg (strand 8-3) | 249 (13.87) | 225 (13.39) | 267 (14.70) | 290 (13.89) | Substrate binding |
| Trp (loop 8-8/9-1) | 251 | 227 | 269 | 292 | Substrate binding (H-bond of substrate to NE1) |
| Met (strand 9-3) | 276 | Trp252 | 306 | Ala332 | Dispersion interactions with substrate |