Substrate-binding could cause a conformational change to take place in the enzyme and reveal an inhibitor binding site, or the inhibitor could bind directly to the enzyme-bound substrate. 

TLS Online TPP Program

#Id: 9635

#Unit 4. Cell Communication and Cell Signaling

Constitutively active Ras proteins (RasD) 

Replacement of the normal glycine 12 with any other amino acid (except proline) blocks the functional binding of GAP proteins and in essence “locks” Ras in the active GTP-bound state.

TLS Online TPP Program

#Id: 9636

#Unit 4. Cell Communication and Cell Signaling

Activated RTKs and cytokine receptors to activate Ras, by two cytosolic proteins — GRB2 and Sos

TLS Online TPP Program

#Id: 9637

#Unit 4. Cell Communication and Cell Signaling

GRB2 is an adapter protein, serves as a link, or scaffold, between the activated receptor and Sos

TLS Online TPP Program

#Id: 9638

#Unit 4. Cell Communication and Cell Signaling

Sos is a GEF that catalyzes conversion of inactive GDP bound Ras to the active GTP-bound form.

TLS Online TPP Program

#Id: 9639

#Unit 4. Cell Communication and Cell Signaling

GRB2 has- 

Phosphotyrosine-binding SH2 domain

Two SH3 domains, bind to Sos

TLS Online TPP Program

#Id: 9640

#Unit 4. Cell Communication and Cell Signaling

The SH3 domains in GRB2 selectively bind to 

proline-rich sequences in Sos