Table 1. Inhibitory and Binding Properties of A1 Site Ligands.
| A1 site ligand | dNTPase inhibition (%, [I] = 500 μM)a | IC50 (μM)b | binding Kd (μM)c | D | Tr (%)d |
|---|---|---|---|---|
| none | 30 | 0 | |||
| rG | 6.0 ± 8.5 | n.d. | 500 ± 185 | 64 | 0 |
| GMP | 7.0 ± 0.7 | n.d. | 110 ± 41 | 87 | 0 |
| GDP | e | e | 210 ± 32 | 88 | 0 |
| GTP | e | e | 61 ± 11 | 64 | 30 |
| 7-Me-GTP | n.t.f | n.t. | >1000 | n.t. |
| dG | 65 ± 2.4 | 130 ± 89 | 79 ± 20 | 80 | 0 |
| dGMP | 75 ± 1.6 | 110 ± 47 | 140 ± 43 | 91 | 0 |
| dGDP | e | e | 130 ± 28 | 39 | 56 |
| acyclovir | 68 ± 31 | n.d. | 160 ± 27 | 78 | 0 |
| 8-oxo-dG | n.t. | n.t. | >1000 | 37 | 0 |
| 8-bromo-dG | n.t. | n.t. | >1000 | 62 | 0 |
| dAMP | 10 ± 0.02 | n.t. | >1000 | 32 | 0 |
| 3′-dGpdA-3′ | 82 ± 2.6 | 102 ± 37 | 41 ± 4.7 | 90 | 0 |
| 3′-dApdA-3′ | 7.0 ± 0.9 | n.t. | >1000 | 33 | 0 |
| 5′-dGpdA-5′ | 50 ± 8.0 | n.t. | 70 ± 13 | 93 | 0 |
| cGAMP | 6.5 ± 3.6 | >1000 | >1000 | 40 | 0 |
| 4 | n.t. | 140 ± 110 | 360 ± 150 | 46 | 0 |
| 1023 | n.t. | 220 ± 150 | >500 | 17 | 0 |
| 5a | n.t. | 8.6 ± 4.1 | 5.2 ± 1.2 | 100 | 0g |
a
Conditions were 1 mM concentration of each ligand and 50 μM GTP and 50 μM dATP.
b
IC50 values were obtained from 11-point dose response curves using the MG colorimetric assay with 50 μM GTP and 50 μM dATP.
c
Competition binding measurements were performed using the 5′ FAM-pdGpdGpdG-3′ probe (see text).
d
Each ligand (500 μM) was incubated with 600 nM SAMHD1 before performing glutaraldehyde cross-linking. D = dimer, T = tetramer.
e
This ligand is an activator of SAMHD1 dNTPase activity.
f
n.t., not tested.
g
200 μM 5a was used in this experiment. All reported errors are SD from at least two replicate experiments.