Table I. Properties of REGγ Lys188 mutants.
| Stimulation of cleavage (x-fold) |
Percentage heptamer | Relative affinity for proteasomea | |||
|---|---|---|---|---|---|
| LLVY | LLR | LLE | |||
| REGγ | 0.4 | 12 | 0.6 | >95 | 100 |
| REGα | 16 | 16 | 9 | ∼95 | 0 |
| γK188E | 14 | 15 | 9 | 50 | 90 |
| γK188D | 14 | 15 | 9 | 50 | 90 |
| γK188A | 6 | 13 | 6 | 60 | 60 |
| γK188C | 6 | 13 | 5 | 70 | 60 |
| γK188N | 5 | 14 | 5 | 80 | 75 |
| γK188Q | 5 | 14 | 5 | 80 | 75 |
| γK188H | 5 | 14 | 4 | >95 | 50 |
| γK188F | 4 | 13 | 4 | dimer | 40 |
| γK188S | 3 | 14 | 3 | >95 | 50 |
| γK188I | 2 | 12 | 3 | >95 | 60 |
| γK188P | 1 | 12 | 1 | 50 | 40 |
| γK188R | 0.7 | 10 | 0.7 | >95 | 75 |
This table summarizes the stability, proteasome activation and relative proteasomal affinity of twelve REGγ Lys188 mutants, compared with those of wild-type REGα and REGγ. Heptamer stability is the percentage of heptamer remaining after rechromatographing 1 mg of each REG heptamer on a Superdex 200 (26/60) column. The activities for proteasome activation are calculated as the fold stimulation: proteasome activity in the presence of 3 µg of each REG species divided by proteasome activity alone. Relative affinity for the proteasome is measured by the inhibition observed after addition of the first 1 µg of REGα(N146Y)/REGβ(N135Y) as shown in the Supplementary data.
aRelative proteasome binding affinity is determined in terms of REGα(N146Y)/REGβ(N135Y) competition and does not reflect the actual proteasomal binding by REG molecules.