Binding of regulator of G protein signaling (RGS) proteins to phospholipid bilayers. Contribution of location and/or orientation to Gtpase-activating protein activity.
Regulator of G protein signaling (RGS) proteins must bind membranes in an orientation that permits the protein-protein interactions necessary for regulatory activity. RGS4 binds to phospholipid surfaces in a slow, multistep process that leads to maximal GTPase-activating protein (GAP) activity. When RGS4 is added to phospholipid vesicles that contain m2 or m1 muscarinic receptor and G(i), G(z), or G(q), GAP activity increases approximately 3-fold over 4 h at 30 degrees C and more slowly at 20 degrees C. This increase in GAP activity is preceded by several other events that suggest that, after binding, optimal interaction with G protein and receptor requires reorientation of RGS4 on the membrane surface, a conformational change, or both. Binding of RGS4 is initially reversible but becomes irreversible within 5 min. Onset of irreversibility parallels initial quenching of tryptophan fluorescence (t(12) approximately 30 s). Further quenching occurs after binding has become irreversible (t(12) approximately 6 min) but is complete well before maximal GAP activity is attained. These processes all appear to be energetically driven by the amphipathic N-terminal domain of RGS4 and are accelerated by palmitoylation of cysteine residues in this region. The RGS4 N-terminal domain confers similar membrane binding behavior on the RGS domains of either RGS10 or RGSZ1.
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041, USA.
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Ross
D000818:Animals; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D006801:Humans; D008051:Lipid Bilayers; D010743:Phospholipids / Q000378:metabolism*; D011485:Protein Binding; D020710:RGS Proteins / Q000378:metabolism*; D051381:Rats
D020690:GTPase-Activating Proteins; D008051:Lipid Bilayers; D010743:Phospholipids; D020710:RGS Proteins