SH3 domains selectively activate the PI3 kinase through non-conventional tertiary contacts

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Signaling

Background:

• Phosphoinositide-3 kinase (PI3K) pathway is crucial for cell metabolism and survival.
• PI3K dysregulation is linked to cancer and other diseases.
• The p85 regulatory subunit inhibits the catalytic p110 subunit.

Purpose of the Study:

• To elucidate the mechanism by which Src homology 3 (SH3) domains activate PI3K.
• To understand how SH3 domains achieve selective PI3K activation despite low intrinsic specificity.
• To investigate the role of tertiary interactions in SH3-mediated PI3K regulation.

Main Methods:

• Structural biology techniques
• Biophysical assays
• Functional cellular assays

Main Results:

• PI3K-activating SH3 domains engage in tertiary interactions with p85 C-terminal domains, relieving p110 inhibition.
• SH3 domains lacking these tertiary contacts bind p85 with similar affinity but do not activate PI3K.
• The p85 subunit utilizes a binding mode-dependent selection mechanism, not solely binding affinity, for PI3K activation.

Conclusions:

• The p85 subunit confers functional selectivity to otherwise promiscuous SH3 domains.
• This mechanism prevents non-specific PI3K activation.
• Provides a framework for predicting, modulating, and targeting SH3-driven PI3K activation in diseases like cancer.