These assays were carried out as previously described (24 ) with minor modifications. Purified GST-fused proteins (15-35 μg) or GST alone (30-45 μg) were immobilized on glutathione S-sepharose beads (GE healthcare) and incubated for 4 hours at 4°C in binding buffer (50 mM Tris-HCl, pH 7.4, 100 mM NaCl, 0.4% (v:v) NP-40, 10 mM MgCl2, 5 mM EDTA, 2 mM DTT, and 2 mM Sodium Orthovanadate) containing sham-treated or in vitro phosphorylated His-GIV CT (aa 1660-1870). After a 4 hour incubation at 4°C, the beads were washed (4.3 mM Na2HPO4, 1.4 mM KH2PO4, pH 7.4, 137 mM NaCl, 2.7 mM KCl, 0.1% (v:v) Tween 20, 10 mM MgCl2, 5 mM EDTA, 2 mM DTT, and 30 and 2 mM Sodium Orthovanadate), and bound proteins eluted in sample buffer for SDS-PAGE. When GST-Gαi3 was used in these assays, both binding and wash buffers were supplemented with 30 μM GDP. Where indicated, His-GIV CT was phosphorylated in vitro using recombinant EGFR (Invitrogen) prior to its use in pulldown assays.
For immunoprecipitations, cell lysates (~1-2 mg protein) were incubated for 4 hours at 4°C with either 2 μg anti-FLAG mAb for immunoprecipitation of GIV-FLAG, anti-GIV-CT (Girdin-T13 Ab, Santa Cruz Biotechnology) for endogenous GIV, anti-HA mAb (Covance) for immunoprecipitation of HA-tagged insulin receptor, anti-EGFR #225 mAb (65 (link)) for immunoprecipitation of endogenous EGFR, and their respective pre-immune control IgGs where indicated. Protein A (for GIV-CT Ab) or G (for all other mAbs) agarose beads (GE healthcare) were added and incubated at 4°C for an additional 60 min. Beads were washed then either resuspended and boiled in SDS sample buffer. Buffers were supplemented with 1 mM sodium orthovanadate for all steps of the assay.
For immunoprecipitations, cell lysates (~1-2 mg protein) were incubated for 4 hours at 4°C with either 2 μg anti-FLAG mAb for immunoprecipitation of GIV-FLAG, anti-GIV-CT (Girdin-T13 Ab, Santa Cruz Biotechnology) for endogenous GIV, anti-HA mAb (Covance) for immunoprecipitation of HA-tagged insulin receptor, anti-EGFR #225 mAb (65 (link)) for immunoprecipitation of endogenous EGFR, and their respective pre-immune control IgGs where indicated. Protein A (for GIV-CT Ab) or G (for all other mAbs) agarose beads (GE healthcare) were added and incubated at 4°C for an additional 60 min. Beads were washed then either resuspended and boiled in SDS sample buffer. Buffers were supplemented with 1 mM sodium orthovanadate for all steps of the assay.