Guanosine triphosphatase stimulation of oncogenic Ras mutants

Area of Science:

• Biochemistry
• Molecular Biology
• Oncology

Background:

• Ras GTPase is a key regulator of cell signaling, frequently mutated in human tumors.
• Oncogenic Ras mutations, particularly at Gly12 and Gln61, lead to impaired GTPase activity and constitutive activation, driving cancer.
• Targeting the Ras GTPase reaction is a significant goal for cancer drug development.

Purpose of the Study:

• To investigate the hydrolysis of a novel guanosine 5'-triphosphate (GTP) analogue, diaminobenzophenone-phosphoroamidate-GTP (DABP-GTP), by wild-type and oncogenic Ras mutants.
• To determine if DABP-GTP can rescue the defective GTPase activity of oncogenic Ras mutants.
• To elucidate the structural and biochemical basis for the interaction between DABP-GTP and Ras.

Main Methods:

• Biochemical assays measuring the hydrolysis of DABP-GTP by wild-type and mutant Ras proteins.
• Crystallographic studies to determine the structure of Ras bound to DABP-GTP analogues.
• Analysis of the role of specific chemical groups within DABP-GTP for its interaction with Ras.

Main Results:

• DABP-GTP is hydrolyzed by both wild-type and oncogenic Ras mutants, with significantly enhanced efficiency for common oncogenic mutants (e.g., Gly12).
• The hydrolysis reaction is independent of Gln61 and is critically dependent on an exocyclic aromatic amino group in DABP-GTP.
• Crystal structures reveal that the DABP-moiety accommodates within the Gly12/Gly13 region, bypassing a rate-limiting step in intrinsic Ras GTPase activity.

Conclusions:

• The defective GTPase switch of oncogenic Ras mutants is not irreversibly damaged and can be rescued by specific GTP analogues like DABP-GTP.
• DABP-GTP's unique chemical structure allows it to overcome the intrinsic GTPase defect in oncogenic Ras.
• These findings provide a foundation for designing novel anti-Ras drugs that target the impaired GTPase reaction.