Signal Termination The Mechanism of GTP Hydrolysis and Conformational Deactivation

Signal Termination The Mechanism of GTP Hydrolysis and Conformational Deactivation 

In most GTP-bound Ga structures, the putative lytic water is positioned less than 4 A from the y phosphorus and, in GaiTGppNp, accepts hydrogen bonds from the main chain amide and side-chain amino group of 

The catalytic glutamine at position 204 in Gail is a conserved feature in all functional Ga proteins, and in most members of the Ras superfamily (residue 61 in Ras). Mutations of this residue in Ga and Ras abolish GTPase activity, are constitutively active, and contribute to cellular transformation (Barbacid, 1987 Bourne et aL, 1991 Gilman, 1987). Further, GTPase activity of the 

The transitions are (1) active site reorganization, (2) formation of the ternary product complex, and (3) product (Pi) release. In this scheme, formation of the chemical transition state occurs at step 2, and the reorganization of the switch segments that lead to effector release occurs in steps 2 and 3. It is probable that the trajectory is more complex, but the scheme serves as a basis for discussion of the data at hand. 

Transition State Formation Is Rate Limiting for Got- Catalyzed GTP Hydrolysis 

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