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The polybasic puzzle: how N-terminal charges modulate Gαi1 membrane behavior and signaling output
Paweł Mystek1, Atte Martikainen2, Ewa Błasiak1
1Department of Physical Biochemistry, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, Kraków, 30-387, Poland.
Cell Communication and Signaling : CCS
|November 26, 2025
Summary
Minor changes in Gαi1 protein arginine residues (R21, R32) significantly alter membrane interactions and impair G protein-coupled receptor (GPCR) signaling, impacting cellular responses.
Area of Science:
- Biochemistry
- Cellular Biology
- Molecular Biophysics
Background:
- G protein-coupled receptors (GPCRs) are crucial for cellular signaling.
- The Gαi subfamily of heterotrimeric G proteins plays a key role in mediating GPCR responses.
- N-terminal polybasic regions of Gαi subunits are critical for membrane association and signaling, despite high sequence similarity.
Purpose of the Study:
- To investigate the functional significance of two specific arginine residues (R21 and R32) in the N-terminal helix of Gαi1.
- To understand how subtle sequence variations in Gαi1 affect its biophysical properties and downstream signaling.
- To elucidate the role of electrostatic charge distribution in Gαi1-membrane and Gαi1-receptor interactions.
Main Methods:
- Site-directed mutagenesis to create specific arginine-to-lysine and alanine substitutions in Gαi1.
- Fluorescence-based techniques including Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Lifetime Imaging Microscopy-Förster Resonance Energy Transfer (FLIM-FRET).
- Cyclic adenosine monophosphate (cAMP) assays and molecular dynamics (MD) simulations.
Main Results:
- Even charge-conserving substitutions of R21 and R32 with lysine significantly altered Gαi1 membrane dynamics and impaired receptor-mediated signaling.
- A double mutant (R21A/R32A) neutralizing local electrostatic charge disrupted nanoscale membrane organization and destabilized the Gαi1β1γ2 complex.
- The R21A/R32A mutation abolished dopamine D2 receptor-mediated cAMP inhibition, despite the residues not directly interacting with Gβγ or adenylyl cyclase.
Conclusions:
- The composition of polybasic motifs is critical for regulating the biophysical and functional properties of peripheral membrane proteins like Gαi1.
- Minor sequence variations, specifically in the spatial charge distribution of N-terminal residues, can profoundly impact GPCR-G protein signaling fidelity.
- Electrostatic interactions with membrane lipids and receptor coupling interfaces are modulated by these N-terminal residues, influencing overall signaling efficiency.
Keywords:
Dopamine D2 receptorFluorescence microscopyGPCRGαi subunitHeterotrimeric g proteinsLipid–protein interactionsMolecular dynamics simulationsMore Related Videos
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