Table 4.
Case 3: SOS functions as a RacGEFa
| 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 without cooperativity | 0.12 | 0.8 | |
| PLCγ-RasGRP binding to and unbinding from LAT | 0.16 | 0.5 | |
| Grb2-SOS unbinding from LAT bound with RasGRP | 0.01 | ||
| Gads activating Rac | 0.007 | ||
| SOS activating Rac when LAT bound with RasGRP | 0.05 | ||
| SOS activating Rac when LAT unbound with RasGRP | 0.0045 | ||
| Rac self-decaying to inactive form | 80 | ||
| Rac activating p38 | 1 | ||
| p38 self-decaying to inactive form | 20 |
a
Grb2-SOS, when bound to LAT, activates Rac directly. RasGRP, when bound to the LAT signalosome, cooperatively enhances SOS RacGEF. Rac can also be activated via a Gads-mediated pathway, but SOS binding to LAT does not contribute to it.