Optimizing PH Domain-Based Biosensors for Improved Plasma Membrane PIP₃ Measurements in Mammalian Cells.

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Pleckstrin homology (PH) domains are crucial for sensing phosphoinositides like phosphatidylinositol 3,4,5-trisphosphate (PIP3).
• Protein-mediated interactions often limit the specificity of PH domain-based biosensors for PIP3.
• Developing specific PIP3 biosensors is essential for understanding cellular signaling pathways.

Purpose of the Study:

• To enhance the specificity of PH domain-based biosensors for PIP3 detection.
• To investigate the impact of mutations disrupting protein interactions on PIP3 biosensor localization and lipid-tracking ability.
• To develop improved GRP1-PH domain constructs for accurate PIP3 signaling analysis.

Main Methods:

• Site-directed mutagenesis was used to alter the PH domains of Akt and GRP1.
• Bioluminescence resonance energy transfer (BRET) and confocal microscopy were employed to assess biosensor localization in HEK293A cells.
• Tandem mutant constructs and Arf6 activity modulation were utilized to evaluate biosensor performance.

Main Results:

• Mutations in GRP1-PH domains significantly reduced plasma membrane localization compared to wild-type and Akt-PH mutants.
• Tandem GRP1-PH constructs demonstrated enhanced PIP3 avidity.
• Mutant GRP1-PH biosensors showed independence from ADP ribosylation factor 6 (Arf6) activity, unlike wild-type sensors.

Conclusions:

• Optimized GRP1-PH domain mutants serve as refined, specific biosensors for dynamic PIP3 signaling.
• These improved biosensors enhance the toolkit for dissecting phosphoinositide-mediated cellular processes.
• The study provides a more accurate system for tracking PIP3 dynamics in real-time.