Table 3.
Case 2: SOS functions as an adaptor onlya
| Reaction | kon (1/s) | koff (1/s) | kcat (1/s) |
|---|---|---|---|
| Gads binding to and unbinding from LAT without cooperativity | 0.1 | 5 | |
| Grb2-SOS binding to and unbinding from LAT | 0.12 | 0.8 | |
| PLCγ-RasGRP binding to and unbinding from LAT | 0.16 | 0.5 | |
| Gads unbinding from LAT bound with RasGRP only | 5 | ||
| Gads unbinding from LAT bound with SOS only | 0.05 | ||
| Gads unbinding from LAT bound with SOS and RasGRP | 0.01 | ||
| Gads activating Rac without cooperativity | 0.005 | ||
| Gads activating Rac when LAT bound with RasGRP only | 0.005 | ||
| Gads activating Rac when LAT bound with SOS only | 0.015 | ||
| Gads activating Rac when LAT bound with SOS and RasGRP | 0.1 | ||
| Rac self-decaying to inactive form | 80 | ||
| Rac activating p38 | 1 | ||
| p38 self-decaying to inactive form | 30 |
a
Grb2-SOS binding to LAT stabilizes the LAT signalosome complex and increases its RacGEF activity; PLCγ-RasGRP's binding further enhances such cooperativity. Grb2-SOS does not activate Rac directly.