Summary of substitutions to putative zinc ligands and nearby residues
| GCP II | Substitution/Activity | Comments | |||||
|---|---|---|---|---|---|---|---|
| His-377 | Gly | no | Ala | no3-a | Gln | no3-a | Zn2+/Hg2+ |
| Asp-379 | Glu | no 3-a | Asn | no 3-a | H-bond | ||
| Asp-387 | Glu | no | Asn | Yes | Leu | no 3-a | Zn2+/Hg2+bridging |
| Pro-388 | Ala | Yes | cis bond | ||||
| Glu-424 | Gln | Yes | Asp | yes3-a | PO4 2−/hydroxamate | ||
| Glu-425 | Gln | no3-a | Asp | no3-a | Zn2+ | ||
| Asp-453 | Glu | yes3-a | Asn | no 3-a | Leu | no 3-a | Zn2+/Hg2+ |
| Ser-454 | Ala | Yes | |||||
| Tyr-552 | Phe | Yes | PO4 2− | ||||
| His-553 | Gly | no | Ala | no | Gln | no3-a | Zn2+ |
Single substitutions are indicated along with the resultant enzyme activity using [3H]NAAG as substrate; “no” indicates no detectable enzyme activity, even after incubations of 16 h. Lower case “yes” indicates very little but detectable activity such that reliable kinetic parameters could not be obtained. See Table 4 for kinetic parameters for mutants indicated by “Yes”. Italics indicate slightly altered migration observed in an immunoblot.
↵3-a Indicates a low level of expression in an immunoblot, see Fig. 2A for examples. See legend for Table 1 for description of comments.