I am trying to study the activation profile of a small G-Protein upon treatment with various kinase inhibitors. To assess the activation profile of this G-protein we employ a protein pull down method using appropriate bait protein conjugated to glutathione agarose beads.  

The protocol I follow is : Cells are harvested in lysis buffer( 50 mM Tris-HCl, pH 7.5, 100 mM NaCl, 2 m0.5 mlTM MgCl2, 0.1% SDS, 0.5% sodium deoxycholate, 1% Triton X-100, 10% glycerol, and HALT protease inhibitor cocktail), spun down at 10,000 rpm for 10 mins. The resultant lysate is incubated with the bait protein conjugated glutathione beads and the pellet is saved separately for analysis. 

The problem is that after certain treatments, the g-protein is translocating to the membrane and is getting stuck in the pellet(as seen by immunoblotting). I have tried sonication and extended incubation time with lysis buffer but it doesn't help in releasing the protein from the membrane(as evidenced by the immunoblot) 

What can I do differently to access this membrane bound protein to make it available for a pulldown assay? Any pointers will be greatly appreciated.