Point mutations in the split PLC-gamma1 PH domain modulate phosphoinositide binding

Area of Science:

• Molecular Biology
• Cell Signaling
• Biochemistry

Background:

• Signaling molecules often utilize pleckstrin homology (PH) domains for binding phosphoinositides and proteins.
• Phospholipase C (PLC)-gamma1 possesses two PH domains: an N-terminal PH(1) and a split PH domain (nPH(2) and cPH(2)).
• Previous work established that the split PH domain of PLC-gamma1 binds phosphatidylinositol 4-phosphate (PI(4)P) and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)).

Purpose of the Study:

• To pinpoint the specific amino acid residues within the PLC-gamma1 nPH(2) domain responsible for PI(4)P and PI(4,5)P(2) binding.
• To investigate the functional consequences of altered phosphoinositide binding on PLC-gamma1 activity and localization.

Main Methods:

• Site-directed mutagenesis was employed to substitute amino acids in the variable loop-1 (VL-1) region of the PLC-gamma1 nPH(2) domain with alanine.
• Phosphoinositide-binding affinities of mutant PLC-gamma1 molecules were assessed using Dot-blot assays with ECL detection.
• Green fluorescent protein (GFP) fusion proteins were utilized to track the membrane translocation of PLC-gamma1 in response to serum stimulation.

Main Results:

• Mutants P500A and H503A within the PLC-gamma1 nPH(2) domain exhibited diminished phosphoinositide-binding affinities.
• These mutant PLC-gamma1 variants displayed reduced hydrolysis of PI(4,5)P(2).
• Both PH(1) and nPH(2) domains were confirmed to be essential for serum-induced membrane targeting of PLC-gamma1.

Conclusions:

• The amino acid residues Proline 500 (Pro(500)) and Histidine 503 (His(503)) are critical for the binding of PLC-gamma1 to PI(4,5)P(2).
• These residues play a vital role in substrate recognition and membrane localization of PLC-gamma1.
• The findings elucidate specific molecular interactions governing PLC-gamma1 function in cellular signaling pathways.