Binding of regulator of G protein signaling (RGS) proteins to phospholipidbilayers - Contribution of location and/or orientation to GTPase-activating protein activty
Yp. Tu et al., Binding of regulator of G protein signaling (RGS) proteins to phospholipidbilayers - Contribution of location and/or orientation to GTPase-activating protein activty, J BIOL CHEM, 276(23), 2001, pp. 20160-20166
Regulator of G protein signaling (RGS) proteins must bind membranes in an o
rientation that permits the protein-protein interactions necessary for regu
latory activity. RGS4 binds to phospholipid surfaces in a slow, multistep p
rocess that leads to maximal GTPase-activating protein (GAP) activity. When
RGS4 is added to phospholipid vesicles that contain m2 or m1 muscarinic re
ceptor and G(i), G(z), or G(q), GAP activity increases similar to3-fold ove
r 4 h at 30 degreesC and more slowly at 20 degreesC, This increase in GAP a
ctivity is preceded by several other events that suggest that, after bindin
g, optimal interaction with G protein and receptor requires reorientation o
f RGS4 on the membrane surface, a conformational change, or both. Binding o
f RGS4 is initially reversible but becomes irreversible within 5 min. Onset
of irreversibility parallels initial quenching of tryptophan fluorescence
(t(1/2) similar to 30 s), Further quenching occurs after binding has become
irreversible (t(1/2) similar to 6 min) but is complete well before maximal
GAP activity is attained. These processes all appear to be energetically d
riven by the amphipathic N-terminal domain of RGS4 and are accelerated by p
almitoylation of cysteine residues in this region. The RGS4 N-terminal doma
in confers similar membrane binding behavior on the RGS domains of either R
GS10 or RGSZ1.