Differential Regulation of Phospholipase C-β₂ Activity and Membrane Interaction by G_q, Gβ₁₂, and Rac2^*

Orit Gutman¹, Claudia Walliser¹, Thomas Piechulek, Peter Gierschik²¹, , and Yoav I. Henis³¹

From the Department of Neurobiology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel, and
the Institute of Pharmacology and Toxicology, University of Ulm Medical Center, Albert-Einstein-Allee 11, 89081 Ulm, Germany

ABSTRACT Back to Top

Abstract: 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 _q and β dimers. We show that activation by _q and β differ from activation by Rac2 and from each other. Stimulation by _q enhanced the plasma membrane association of PLCβ₂, but not of PLCβ₂, which lacks the _q-interacting region. Although _q 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 _q 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 β shifted the FRAP of PLCβ₂ and PLCβ₂ 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 _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 β recruits PLCβ₂ to the membrane by transient interactions, leading to fast "surfing" diffusion along the membrane, sampling large regions for dispersed PtdInsP₂ populations.

Key Words: G Proteins • Heterotrimeric G Proteins • Membrane Biophysics • Membrane Lipids • Phospholipase C • FRAP • Lateral Diffusion • Rac

Received for publication November 13, 2009.

FOOTNOTES Back to Top

² To whom correspondence may be addressed. Tel.: 49-731-5006-5500; Fax: 49-731-5006-5502; E-mail: peter.gierschik{at}uni-ulm.de.

³ An incumbent of the Zalman Weinberg Chair in Cell Biology. To whom correspondence may be addressed. Tel.: 972-3-640-9053; Fax: 972-3-640-7643; E-mail: henis{at}tauex.tau.ac.il.

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