Differential Regulation of Phospholipase C-β2 Activity and Membrane Interaction by Gαq Gβ1γ2 and Rac2

摘要

We combined fluorescence recovery after photobleaching (FRAP) beam-size analysis with biochemical assays to investigate the mechanisms of membrane recruitment and activation of phospholipase C-β2 (PLCβ2) by G protein αq and βγ dimers. We show that activation by αq and βγ differ from activation by Rac2 and from each other. Stimulation by αq enhanced the plasma membrane association of PLCβ2, but not of PLCβ2Δ, which lacks the αq-interacting region. Although αq resembled Rac2 in increasing the contribution of exchange to the FRAP of PLCβ2 and in enhancing its membrane association, the latter effect was weaker than with Rac2. Moreover, the membrane recruitment of PLCβ2 by αq occurred by enhancing PLCβ2 association with fast-diffusing (lipid-like) membrane components, whereas stimulation by Rac2 led to interactions with slow diffusing membrane sites. On the other hand, activation by βγ shifted the FRAP of PLCβ2 and PLCβ2Δ to pure lateral diffusion 3- to 5-fold faster than lipids, suggesting surfing-like diffusion along the membrane. We propose that these different modes of PLCβ2 membrane recruitment may accommodate contrasting functional needs to hydrolyze phosphatidylinositol 4,5-bisphosphate (PtdInsP₂) in localized versus dispersed populations. PLCβ₂ activation by Rac2, which leads to slow lateral diffusion and much faster exchange, recruits PLCβ₂ to act locally on PtdInsP₂ at specific domains. Activation by α_q leads to lipid-like diffusion of PLCβ₂ accompanied by exchange, enabling the sampling of larger, yet limited, areas prior to dissociation. Finally, activation by βγ recruits PLCβ₂ to the membrane by transient interactions, leading to fast “surfing” diffusion along the membrane, sampling large regions for dispersed PtdInsP₂ populations.