Gα_s-specific structural elements attenuate interactions with regulator of G protein signaling (RGS) proteins

Area of Science:

• Molecular biology
• Biochemistry
• Structural biology

Background:

• Heterotrimeric G proteins (αβγ) act as molecular switches regulated by G protein-coupled receptors (GPCRs).
• Regulators of G protein signaling (RGS) proteins inactivate Gα subunits, controlling signaling duration by accelerating GTP hydrolysis.
• Gαs is unique as it does not interact with known RGS proteins, a phenomenon not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying the lack of interaction between Gαs and RGS proteins.
• To identify specific structural features or residues responsible for Gαs's divergent interaction profile with RGS proteins.

Main Methods:

• Comparative structural analysis of experimental and modeled Gαs structures.
• Functional biochemical assays, including mutagenesis and GTPase-activating protein (GAP) activity measurements.
• In silico modeling to predict structural interactions.

Main Results:

• Gαs possesses unique structural elements in its helical and GTPase domains compared to other Gα subunits.
• Modeling suggested potential interference with RGS binding due to helical domain insertions or GTPase domain residues.
• Mutagenesis identified three specific residues in the Gαs GTPase domain as necessary and sufficient to prevent RGS-mediated inactivation.
• Substituting these Gαs residues with those from Gαi1 rendered Gαs susceptible to RGS inactivation.

Conclusions:

• The unique structure of the Gαs GTPase domain, specifically three residues, directly prevents inactivation by RGS proteins.
• These findings reveal the mechanistic basis for G protein specificity in RGS interactions.
• Understanding this divergence provides insights into the regulation of G protein signaling pathways.