Table 4.
Active site elements of inverting and retaining glycosidases
| Lysozyme | T4L
|
HEWL | GEWL* | ||
|---|---|---|---|---|---|
| WT | T26E | T26H | |||
| (A) Acid/base catalyst | Glu-11 (Oɛ2) | Glu-11 (Oɛ2) | Glu-11 (Oɛ2) | Glu-35 (Oɛ1) | Glu-73 (Oɛ1) |
| (B) General acid | Asp-20 (Oδ1) | — | — | — | Asp-97 (Oδ2) |
| (C) Nucleophile/leaving group | (H2O) | Glu-26 (Oɛ1) | His-26 (Nɛ2) | Asp-52 (Oδ2) | (H2O) |
| Separation A–B, Α | 7.2 | 9.0 | |||
| Separation A–C, Å | 5.7 | 5.3 | 5.9 | 6.2 | n.d. |
| Configuration of products | α | Covalent adduct | β | β | α |
| Transglycosylase | No | n.d. | Yes | Yes | n.d. |
n.d., not determined.
*
In GEWL Asp-97 is thought not to participate in catalysis (24). Its distance from Glu-73 is given for reference. The location of the solvent that acts as the presumed nucleophile has not been determined.