Fig. 2. Effect of Tris-grafting degree on membrane protein solubilization and size of AcrB–NCMN particles therefrom. (A) The typical procedure applied in the solubilization and purification of membrane proteins in this work. (B) Ni–NTA affinity chromatography profiles of purified AcrB in different NCMN polymers. (C) Analysis of AcrB–NCMN particles on SDS-PAGE along with protein marker (M). Lanes 1, 2, 3, and 4 correspond to purified AcrB extracted by NCMNP2a-5, NCMNP2a-25, NCMNP2a-50, and NCMNP2a-70, respectively. (D) Negative stain analysis of AcrB particles extracted by NCMNP2a-x polymers (x = 5, 25, 50, and 70). The bottom-left scale bar represents 50 nm. (E) Compositions of lipid species extracted from membrane fraction and purified AcrB determined by ESI-MS. Abbreviations included are cardiolipin (CL), cholesterol ester (ChE), coenzyme (Co), diglyceride (DG), phosphatidylcholines (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylserine (PS), sphingomyelin (SPH) and triglyceride (TG).