Functional and structural characterization of allosteric activation of phospholipase Cε by Rap1A

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Signaling

Background:

• Phospholipase Cε (PLCε) is a key enzyme activated by G protein-coupled receptors and receptor tyrosine kinases.
• Small GTPases like Ras and Rap1A are known to interact with PLCε, but the mechanism of Rap1A activation remains unclear.

Purpose of the Study:

• To investigate whether Rap1A activates PLCε and elucidate the molecular mechanism of this activation.
• To determine the specific domains and residues of PLCε involved in Rap1A binding and activation.

Main Methods:

• Protein purification and in vitro binding assays.
• Site-directed mutagenesis to identify key residues.
• Small-angle X-ray scattering (SAXS) to study conformational changes.
• Utilized existing structural data of PLCε.

Main Results:

• Confirmed that the C-terminal Ras association (RA2) domain of PLCε is essential for Rap1A activation.
• Demonstrated that the pleckstrin homology (PH) domain and EF1/2 hands of PLCε are also required for Rap1A-mediated activation.
• Identified critical hydrophobic residues on the RA2 domain surface necessary for Rap1A interaction.
• SAXS revealed that Rap1A binding induces and stabilizes distinct conformational states in PLCε.

Conclusions:

• Rap1A allosterically activates PLCε by promoting and stabilizing interactions between the RA2 domain and the enzyme's core.
• This mechanism is analogous to Ras activation of PLCε, providing a unified view of GTPase-mediated lipase activation.