Crystal structure and functional analysis of Ras binding to its effector phosphoinositide 3-kinase gamma

Area of Science:

• Molecular Biology
• Cellular Signaling
• Structural Biology

Background:

• Ras activation of phosphoinositide 3-kinase (PI3K) is vital for the survival of transformed cells.
• Understanding the direct molecular interactions between Ras and PI3K is key to deciphering cancer cell proliferation.

Purpose of the Study:

• To investigate the direct activation mechanism of PI3Kgamma by Ras.
• To determine the structural basis of Ras-PI3Kgamma interaction.
• To explore the implications of these interactions for cancer cell survival.

Main Methods:

• In vivo and in vitro activation assays using H-Ras G12V and GTPgammaS-loaded H-Ras.
• Determination of the crystal structure of a PI3Kgamma/Ras.GMPPNP complex.
• Site-directed mutagenesis to analyze critical interaction regions.

Main Results:

• PI3Kgamma is strongly and directly activated by H-Ras.
• The crystal structure reveals a critical loop positioning Ras via its switch I and switch II regions for PI3Kgamma binding.
• Mutagenesis confirms the necessity of these Ras regions for PI3Kgamma interaction, alongside direct contact with the catalytic domain.

Conclusions:

• Specific structural interactions mediate the direct activation of PI3Kgamma by Ras.
• These findings suggest a conserved activation mechanism potentially shared with PI3Kalpha.
• The observed conformational changes in PI3Kgamma indicate an allosteric component in Ras-mediated activation, relevant for cancer therapy.