Molecular basis for Gβγ-mediated activation of phosphoinositide 3-kinase γ

Area of Science:

• Biochemistry
• Cell Biology
• Structural Biology

Background:

• Phosphoinositide 3-kinase gamma (PI3Kγ) catalyzes the conversion of PIP2 to PIP3, a key signaling event.
• This process is vital for neutrophil chemotaxis and implicated in cancer metastasis.
• PI3Kγ activation depends on its interaction with Gβγ heterodimers released from G protein-coupled receptors (GPCRs).

Approach:

• Utilized cryo-electron microscopy (cryo-EM) to determine the structures of PI3Kγ-Gβγ complexes.
• Analyzed complexes with various substrates and analogs to understand activation mechanisms.
• Employed biochemical assays with protein variants to probe the function of Gβγ binding sites and allosteric regulation.

Key Points:

• Identified two distinct Gβγ binding sites on PI3Kγ: one on the p110γ helical domain and another on the p101 subunit.
• Observed conformational changes in the PI3Kγ kinase domain upon Gβγ binding, mimicking Ras·GTP induced changes.
• Demonstrated that Gβγ binding not only recruits PI3Kγ to membranes but also allosterically modulates its activity through both binding sites.

Conclusions:

• Gβγ binding to PI3Kγ involves dual sites and induces allosteric conformational changes that regulate enzyme activity.
• Findings provide mechanistic insights into Gβγ-mediated PI3Kγ activation, relevant to neutrophil migration and cancer.
• The structural and mechanistic understanding will facilitate the development of PI3Kγ-selective drugs.