| |
Reaction
Name | Pathway Name /
Pathway No. | Kf | Kb | Kd | tau | Reagents |
| 1 | Shc_bind_
Sos.Grb2 | Sos
Pathway No. 33 | 0.5
(uM^-1 s^-1) | 0.1
(s^-1) | Kd(bf) = 0.2(uM) | - | Substrate:
Sos.Grb2
SHC*
Products:
Shc*.Sos.Grb2
|
| Sasaoka et al JBC 269:51 pp 32621 1994, table on pg 32623 indicates that this pathway accounts for about 50% of the GEF activation. (88% - 39%). Error is large, about 20%. Fig 1 is most useful in constraining rates. Chook et al JBC 271:48 pp 30472, 1996 say that the Kd is 0.2 uM for Shc binding to EGFR. The Kd for Grb direct binding is 0.7, so we'll ignore it. | | 2 | Grb2_bind_Sos* | Sos
Pathway No. 33 | 0.025
(uM^-1 s^-1) | 0.0168
(s^-1) | Kd(bf) = 0.672(uM) | - | Substrate:
Sos*
Grb2
Products:
Sos*.Grb2
|
| Same rates as Grb2_bind_Sos: Porfiri and McCormick JBC 271:10 pp 5871 1996 show that the binding is not affected by the phosphorylation. | | 3 | Grb2_bind_Sos | Sos
Pathway No. 33 | 0.025
(uM^-1 s^-1) | 0.0168
(s^-1) | Kd(bf) = 0.672(uM) | - | Substrate:
Grb2
Sos
Products:
Sos.Grb2
|
| As there are 2 SH3 domains, this reaction could be 2nd order. I have a Kd of 22 uM from peptide binding (Lemmon et al JBC 269:50 pg 31653). However, Chook et al JBC 271:48 pg30472 say it is 0.4uM with purified proteins, so we believe them. They say it is 1:1 binding. Porfiri and McCormick JBC 271 also have related data. After comparing with the time-course of 1 min and the efficacy of activation of Ras, settle on Kd of 0.672 which is close to the Chook et al value. | | 4 | dephosph_Sos | Sos
Pathway No. 33 | 0.001
(s^-1) | 0
(s^-1) | - | - | Substrate:
Sos*
Products:
Sos
|
| The best clue I have to these rates is from the time courses of the EGF activation, which is around 1 to 5 min. The dephosph would be expected to be of the same order, perhaps a bit longer. Lets use 0.002 which is about 8 min. Sep 17: The transient activation curve matches better with kf = 0.001 |
and 
color.
