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The Pleckstrin Homology Domain of PLCδ1 Exhibits Complex Dissociation Properties at the Inner Leaflet of Plasma Membrane Sheets

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posted on 28.05.2021, 19:16 by Madeline R. Sponholtz, Eric N. Senning
Using total internal reflection fluorescence microscopy, we followed the dissociation of GFP-tagged pleckstrin homology (PH) domains of AKT and PLCδ1 from the plasma membranes of rapidly unroofed cells. We found that the AKT-PH-GFP and PLCδ1-PH-GFP dissociation kinetics can be distinguished by their effective koff values of 0.39 ± 0.05 and 0.56 ± 0.16 s–1, respectively. Furthermore, we identified substantial rebinding events in measurements of PLCδ1-PH-GFP dissociation kinetics. By applying inositol triphosphate (IP3) to samples during the unroofing process, we measured a much larger koff of 1.54 ± 0.42 s–1 for PLCδ1-PH-GFP, indicating that rebinding events are significantly suppressed through competitive action by IP3 for the same PH domain binding site as phosphatidylinositol 4,5-bisphosphate (PIP2). We discuss the complex character of our PLCδ1-PH-GFP fluorescence decays in the context of membrane receptor and ligand theory to address the question of how free PIP2 levels modulate the interaction between membrane-associated proteins and the plasma membrane.